Orchestral Accompaniment Techniques

This invention relates to electronic musical instruments, and more particularly relates to such instruments capable of providing an accompaniment to a melody played by a performer.

Electronic musical instruments, such as keyboard-controlled electronic organs, have experienced wide acceptance among musicians. Since many of these instruments are sold to amateurs, manufacturers have placed special emphasis on the ease of playing and on the variety of voices (i.e., sound qualities or timbres) available to the performer. In particular, the electronic musical instrument industry has long sought a method of producing a full orchestral accompaniment which can be controlled easily by a performer of limited skill or musical knowledge.

Past attempts in this direction have met with only limited success. For example, it is possible to play a complete accompaniment chord on some instruments (e.g., chord organs) by pressing only one key. The drone of such instruments may sound good to the novice, but it soon becomes monotonous. The drone of the chord organs has been reduced somewhat by a variety of rhythm devices consisting of synthetically created drum, brush and cymbal sounds which are selectively gated on and off in accordance with a rhythm clock. Bass tones consisting of a root note, a fifth, or similar elementary harmonic structures, have been generated by prior rhythm devices, but they have not relieved the monotony inherent in such devices. Other instruments, such as the Yamaha Model E-70 electronic organ, gate solid pitched chords on and off with a rhythm clock and simultaneously generate a running base line which keys a variety of pitches on and off with the rhythm clock. The solid chords sound in the registration selected on a lower keyboard manual and the bass line sounds in the registration selected on the pedal board. For any given chord selected by the performer, the gated chords remain the same and the melodic pattern of the base line remains the same during a prescribed musical segment of about two measures.

More recent instruments such as the Lowrey Model D-325, key a melody line and a running bass line on and off with a rhythm clock. Solid chords also can be controlled by the same rhythm clock. The solids chords and melody line sound in selectable registration and the bass line sounds in another selectable registration.

There have been attempts to synthesize music on a digital computer. For example, the May, 1961 Bell System Technical Journal contains a description by Max V. Mathews of "An Acoustic Compiler For Music And Psychological Stimuli". A related device was developed at Dartmouth College and is described in a May, 1975 paper by Paul Tobias entitled, "An Introduction To The Dartmouth Music Language". Such music synthesizers are able to simulate orchestral affects to a greater extent than the instruments described above. However, it is believed that no one has been able to incorporate such synthesizers into a performing instrument capable of responding to the touch of a performing musician.

Although the foregoing devices are a step in the right direction, the resulting sound does not compare with the results obtained when a skilled organist plays an instrument by adding correct counterpoint, countermelody, variable rhythm patterns and other embellishments that only a skilled musician can employ. Even a skilled keyboard player cannot duplicate or effectively emulate a group of different instruments or an orchestra, because, at any one time, each key of a single keyboard controls tones having the same voice or timbre. That is, the player cannot produce totally different timbres of sound on keys played simultaneously on the same keyboard. As a result, he cannot hope to produce a truly orchestral effect.

Accordingly, it is a principal object of the present invention to enable a performer to create an accompaniment in a proper harmony and in a variety of different styles types of music, such as bossa nova, big band, baroque, jazz guitar, contemporary guitar and celli, country and western, hillbilly, bluegrass, rock and roll, etc. in which one or more of the instrumentation pattern, rhythm pattern, chord pattern pattern and melodic contour can be changed under performer control in order to add variety to the accompaniment.

Another object is to produce a musical instrument of the foregoing type in which one or more of the rhythm pattern, chord pattern pattern and melodic contour are changed in response to a change in harmony by the performer.

Yet another object is to provide an instrument of the foregoing type in which one or more of the instrumentation pattern, chord pattern pattern and melodic contour are changed in response to a change in musical style by the performer.

Still another object is to provide an instrument of the foregoing type in which the performer can use a keyboard in order to select the proper harmony for the accompaniment.

Still another object is to provide an instrument of the foregoing type in which mistakes in musical phrasing by the performer are corrected or minimized.

Yet another object is to provide an instrument of the foregoing type in which multiple voice lines are individually controlled in order to simulate the sound of a true orchestra.

An electronic musical instrument built according to this specification combines great ease of playing with an improved tone production system that faithfully reproduces the various instruments and rhythm patterns of an orchestra. The instrument automatically creates an accompaniment in the pitch range and rhythmic patterns that the experienced music arranger or orchestrator uses to define different styles of music. As a result, a performer of limited skill or musical knowledge can easily play a complete orchestral accompaniment in any one of a variety of musical styles. In order to achieve this result, the inventors have discovered new techniques for storing musical parameter information in a memory and processing that information according to the playing of the instrument by the performer.

These and other objects, advantages and features of the present invention will appear for purposes of illustration, but not of limitation, in connection with the accompanying drawings, wherein like numbers refer to like parts throughout, and wherein:

FIGS. 1-14 illustrate musical techniques which the preferred embodiment of the invention is capable of producing;

FIG. 15 is a logical block diagram of a preferred form of musical instrument made in accordance with the present invention;

FIG. 16 is an electrical schematic diagram of a preferred form of a microprocessor made in accordance with the present invention;

FIG. 17 is a block diagram illustrating the operation of certain registers in the microprocessor;

FIG. 18 is a chart illustrating the general operation of the registers shown in FIG. 17;

FIG. 19 is a flow chart illustrating the manner in which the processor determines the harmony desired by a performer;

FIG. 20 is an electrical schematic diagram of a preferred form of oscillator made in accordance with the present invention;

FIG. 21 is an electrical schematic diagram of a preferred form of duty cycle adjustment circuit made in accordance with the present invention; FIG. 21A is a timing diagram illustrating voltage waveforms generated by the like-lettered parts of the circuit shown in FIG. 21;

FIG. 22 is an electrical schematic diagram of a preferred form of programmable filter made in accordance with the present invention;

FIG. 23 is an electrical schematic diagram of a preferred form of envelope generator made in accordance with the present invention;

FIG. 24 is a timing diagram illustrating voltage waveforms generated by the like lettered parts of the envelope generator shown in FIG. 23;

FIG. 24A is an electrical schematic diagram of a preferred form of modulator made in accordance with the present invention;

FIGS. 25-30 and 32 are flow charts illustrating the overall operation of the preferred embodiment; and

FIG. 31 is a diagram illustrating the organization of the orchestration tables stored in the memory of the preferred embodiment.

An electronic musical instrument made in accordance with the preferred embodiment of the invention is capable of providing a full orchestral accompaniment to a melody played in any one of the 12 possible harmonic keys. The accompaniment easily can be controlled by the left hand of a performer who is playing the melody with his right hand on a melody keyboard. The accompaniment is "played" by the instrument in any one of a variety of different musical "styles", such as bossa nova, big band, baroque, jazz guitar, or contemporary guitar and celli. The musical style desired by the performer is selected by a switch located on the instrument console. The performer also adjusts a tempo clock so that the accompaniment is "played" by the instrument in time with the melody being played by the performer.

The instrument automatically relates the accompaniment to the harmony selected by the left hand of the performer on a harmony keyboard. Thus, the accompaniment is "played" both in the style and harmony selected by the performer as most appropriate for the melody he is playing.

The instrument normally generates a segment or orchestrated accompaniment music which is repeated after every two musical bars. That is, a normal segment of accompaniment music consists of two musical measures or bars, and each bar contains four musical beats. A waltz segment consists of two bars, and each bar contains three beats.

The instrument analyzes the manipulation of the harmony keyboard in order to ascertain the accompaniment harmony desired by the performer. In particular, the instrument identifies a specified chord type and root note. The chord types recognized by the instrument are major, minor, diminished, augmented and seventh, and the root note can be any of the twelve notes of the musical chromatic scale.

In order to add variety to the musical accompaniment segments, the twelve possible roots are divided into four groups as follows:

(Throughout this specification, a musical sharp is indicated by the symbol .sup..music-sharp..)

Assuming the musical style selected by the performer remains constant, the segment of accompaniment music produced by the instrument changes each time the performer plays a new chord type or a chord in a new root group. Since there are five possible chord types and four possible root groups, twenty different and unique musical segments can be produced for each musical style. In other words, for any given style of music, there are twenty different music segments arranged to express the style. This is a unique feature which causes the expression of any musical style to change as the harmony desired by the performer changes, thereby adding vitality and variety to the accompaniment.

An electronic musical instrument made in accordance with the preferred embodiment enables a performer easily to produce a wide variety of musical techniques which cannot be achieved at any level of complexity by existing electronic musical instruments. Many of these techniques are illustrated in FIGS. 1-14. Each of FIGS. 1-14 is subdivided into three sections:

Section I identifies the musical style selected by the performer;

Section II illustrates the notes played by the performer on the harmony keyboard in order to indicate the harmony he desires, as well as the chord type, root and root group which the instrument identifies based on the notes played by the performer;

Section III illustrates (a) the two bar accompaniment produced by the instrument in response to the notes played by the performer, (b) the notes added by the instrument which are not in the chord played by the performer, and (c) the rhythm pattern produced by the instrument.

An electronic musical instrument made in accordance with the preferred embodiment is capable of generating unique accompaniment musical segments employing one or more of the following musical techniques:

1. The rhythm pattern of the musical segment changes when the performer changes from one root group or one chord type to another;

2. The melodic contour of the musical segment changes when the performer changes from one root group or chord type to another;

3. The chord pattern pattern of the musical segment changes when the performer changes from one root group or chord type to another;

4. Harmonies different from the harmony nominally selected by the performer are played (e.g., a chord is played having a different name from the chord played by the performer);

5. Chord progressions result from a single chord played by the performer;

6. The octave positions of the notes of a chord played by the performer are changed depending on the tone quality or instrument being simulated in order to achieve chord voicing;

7. Musical figures are presented in contrapuntal form with the melody played by the performer functioning as a cantus firmus (i.e., primary melody), or the musical segment is presented as an accompaniment having two or more contrapuntal parts;

8. The instrumentation pattern of the notes of the musical segment changes when the performer changes from one style to another, so that instruments appropriate to the selected style can be simulated.

9. The rhythm pattern, melodic contour or chord pattern pattern produced by the instrument change when the performer changes from one style to another, so that the musical segment accurately expresses the style.

No known prior electronic instrument is capable of implementing any of these techniques under playing control by a performer. The ability of the present instrument to produce musical segments employing these techniques is a significant advance in the art which dramatically increases the ability of a performer to make interesting and vital music. Those able to read music will recognize from FIGS. 1-14 additional musical techniques which enhance the orchestrated accompaniment produced by the present instrument.

Regarding musical technique 1, FIGS. 5 and 6 illustrate the fact that the rhythm pattern for the big band style changes when the performer switches from a major chord type to a minor chord type. FIGS. 1 and 2 indicate that the rhythm patterns also change when the performer switches from one root group to another, even though the chord type remains the same. This is an important feature which adds a great deal of variety and interest to the resulting music.

Regarding technique 2, each of FIGS. 1-14 illustrate the fact that the melodic contour is varied when the performer changes either from one root group or one chord type to another. As used in this specification and these claims, melodic contour refers to the relative pitch intervals of a melody line of the accompaniment. Transposing a melody line from one harmonic key to another would not change the melodic contour because the relative pitch intervals in the different keys would remain the same. Changing the pitch interval of one note in a melody line relative to another note in the melody line would change the melodic contour.

Regarding technique 3, FIGS. 1-14 each illustrate the chord pattern changing ability of the instrument in musical segments employing a plurality of chords having different chord component structures these claims, harmonic pattern refers to the relative. As used in this specification and these claims, changing the chord component structure of a chord refers to changing the relative pitch intervals of the notes in the chord, by adding, deleting or modifying notes in the chord, other than by changing the octave locations of one or more notes of the chord. As used in this specification and claims, chord pattern refers to the order in which chords of different chord component structures are sounded. Transposing a segment of the accompaniment from one harmonic key to another would not involve a change in chord interval structure or chord pattern. Changing the pitch interval of one note in a chord relative to another note in the chord, other than by changing the octave location of one or more notes of the chord, would change the chord interval structure. For example, harmonic inversions, as shown by chords X and Y of FIG. 10, change only the octave locations of the notes of the chords and therefore do not change the chord interval structure. As used in this specification and these claims, to harmonically modulate means to change a chord pattern in ways other than those required to accommodate a change in chord type selected by the performer. In a musical segment generated in response to a major chord which includes as major 6th chord followed by a minor seventh chord, altering the segment to a minor 6th chord followed by a minor 7th chord in response to the selection of a minor chord by the performer would not harmonically modulate the segment. Altering the segment to a minor 7th chord followed by a minor ninth chord would harmonically modulate the segment.

Regarding techniques 4 and 5, FIG. 5 is a particularly good illustration of the chord progression and harmony changing capabilities of the instrument.

Regarding technique 6, each of FIGS. 1-14 illustrates the chord voicing capabilities of the instrument.

Regarding technique 7, FIGS. 7-10 and 13 illustrate various contrapuntal forms of music, as well as counter melodies, which can be produced by the instrument.

Each of FIGS. 1-14 illustrates techniques 8 and 9. As used in this specification and these claims, instrumentation pattern refers to the combination of different instrument sounds or timbres in which a style is expressed by pitched notes. For example, if the timbre of sound expressing one voice line of pitched notes in a segment of music is changed to a different timbre, the instrumentation pattern also is changed.

Referring to FIG. 15, a preferred form of electronic musical musical instrument capable of producing the foregoing musical techniques under the control of a performer basically comprises a melody system 30, a harmony selection system 86, a musical style selector 140, a processing system 150 and an output system 250. As shown in FIG. 15, melody system 30 includes a conventional melody keyboard 32 which comprises playing keys 35-71. Each of the keys represents at least one note which is pitched in at least one octave. Keyboard 32 is connected through a cable 73 to conventional electronic organ circuitry 75. The circuitry produces audio tone signals based on the melody keys depressed by the performer in a well-known manner. The tone signals are transmitted through an output amplifier 77 to a conventional loud-speaker transducer 79 which converts the signals to sound.

Harmony selection system 86 comprises a harmony keyboard 88, including playing keys 90-126. The keys operate switch contacts 133 which correspond to switches 23 described in U.S. Pat. No. 3,745,225 (Hall-July 10, 1973, hereafter the "'225 Patent"). The switch contacts are connected to output conductors 134 (corresponding to conductors 24 of the '225 Patent) by a coupling network 135 of the same type described in that patent. Conductors 134 are connected to a conventional 12 bit latch 138 which can be addressed and read by processing system 150.

Each of the keys of keyboard 88 represents at least one note pitched in at least one octave. One such note and octave is printed on the keys in FIG. 15. For example, key 90 is used to produce at least a C note pitched in octave 1, and key 106 is used to produce at least an E note pitched in octave 2. As explained in the '225 Patent, coupling network 135 is arranged so that the playing of any key on keyboard 88 which corresponds to a C note results in a logical one signal on the C conductor of group 134, irrespective of the octave in which the C note is pitched. For example, the C conductor in group 134 will be raised to a logical one state if any or all of keys 90, 102, 114 or 126 are depressed by a performer. As a result, the input to latch 138 represents each of the notes produced by a performer's manipulation of keyboard 88, but does not indicate in which octave any of the notes are pitched.

Musical style selector 140 comprises switches 142-146 by which a performer can select any one of the musical styles referred to in FIGS. 1-14. In response to the depression of one of switches 142-146, an accompaniment-type selection signal, preferably in the form of an eight bit word corresponding to the desired style, is stored in a conventional eight bit register contained within selector 140. The word is read by processing system 150 and is used in a manner described later. Of course, the instrument could be expanded to include other musical styles, depending on the size of the processing system desired. Those skilled in the art readily will be able to expand the scope of the instrument to include other musical styles based on the present teaching.

Referring to FIGS. 15 and 16, processing system 150 comprises a communication bus 152 that is subdivided into an eight bit data bus 154, a sixteen bit address bus 155, a four bit read-write bus 156, an interrupt line 157 and a clock line 158.

The processing system also includes a program read only memory (ROM) 162 which stores instructions for the overall system. An orchestration and instrument ROM 164 stores digital information necessary for the production of the musical segments. A general purpose random access memory (RAM) 166 is used to hold intermediate variables and working data pointers used by a microprocessor 170 which performs sequential programmed logic functions in order to operate the system.

Referring to FIG. 16, microprocessor 170 comprises a central processor unit 172 which may be a general purpose microcomputer, such as model 8080 manufactured by Intel Corporation. The microprocessor also includes a processor clock 174 which may be a model 8224 manufactured by Intel Corporation, and a system controller 176 which may be a model 8228 manufactured by Intel Corporation. The microprocessor also includes amplifiers 180-200, diodes 206-207, capacitors 210-212, resistors 216-220, and a crystal 222, all connected as shown.

Referring to FIG. 17, microprocessor 170 also includes a four bit register 224 and an eight bit register 226 that comprises a carry bit CY, a most significant bit MSB and a least significant bit LSB. The purpose of a shift counter bit 228 is described later.

Referring to FIG. 15, a tempo clock 232 is provided in order to synchronize the system with the performer. The tempo clock may be speeded up or slowed down to suit the tempo at which the performer wishes to play. The tempo is established by rotating knob 234 which adjusts the rate at which tempo clock pulses are generated.

The tempo clock issues twelve tempo clock pulses per musical beat so that it can resolve a quarter note beat into eighth notes, sixteenth notes or triplets. A normal musical bar consists of four beats; each bar is broken into two parts, each of which has two beats. A waltz-type bar consists of three beats; each bar is broken into two parts, the first part being two beats and the second part being one beat.

The tempo clock is used by the system to establish a pattern for the repetition of the two bar musical segments, such as those illustrated in FIGS. 1-14. A segment is repeated after every two bars. That is, a normal segment consists of two normal bars, each made up of four beats so that an eight beat pattern results. A waltz segment consists of two waltz bars having three beats per bar, so that a six beat pattern results. A (4/4) time switch 235 and a (3/4) time switch 236 enable a performer to adjust the output of the tempo clock to the appropriate time pattern. Tempo clock 232 generates a downbeat pulse at the beginning of each musical bar which synchronizes the system in a manner described later. The downbeat pulse and tempo clock pulses are transmitted to other parts of the system over data bus 154 and conductor 238.

Harmony selection system 86 cooperates with processing system 150 in order to recognize the harmony indicated by the depression of one or more keys of keyboard 88 by the performer. Of course, the preferred embodiment could be implemented with a chord organ-type pushbutton system in which a separate button is provided for each chord type and root note desired by the performer. However, such a pushbutton system is not satisfying to the more advanced musician who is used to playing on a keyboard in order to establish the harmony of his musical performance.

By using the following technique, the harmony desired by the performer can be recognized solely from his manipulation of keyboard 88. As used in this specification and claims, harmony means chord structure defined by chord type and root note. In order to recognize any chord type, the microprocessor attempts to match a representation of a playing key pattern with a corresponding chord type and root. In order to achieve this result, signal-responsive representations of various playing key patterns are stored in memory. A performer may express a desire for a particular chord type based on a particular root by depressing the playing keys according to a number of different patterns. For example, the performer may express a desire for C minor harmony (i.e., chord type minor, root C) by actuating any one of the following key patterns:

1. C, D.sup..music-sharp.

2. C, D.sup..music-sharp., G

3. C, D.sup..music-sharp., G, B

4. C, D.sup..music-sharp., B

5. D.sup..music-sharp., F, A.sup..music-sharp.

6. C, D.sup..music-sharp., F, A.sup..music-sharp.

7. C, D.sup..music-sharp., F, G

These key patterns can be used by the processor in several ways in order to derive a chord type signal indicating the chord type desired by the performer and a root signal indicating the root note of the harmony desired by the performer. For example, the playing key patterns can be converted to digital signals representing addresses of memory locations which store signals defining the corresponding chord type and root of the key pattern. If the memory locations store the chord type and root signals at addresses corresponding to the key pattern representations, the chord type and root signals may be obtained by merely reading their values from the memory. In such an embodiment, the stored signal-responsive representations of the key patterns are created by the circuitry forming the memory addressing logic. This technique results in rapid processing, but requires a considerable amount of memory.

Alternatively, an algorithm could be developed which would represent each of the key patterns desired to be recognized as a particular chord type. In this case, the algorithm would be stored as a general representation of the key patterns.

As another alternative, the various key pattern representations can be stored as chord pattern signals in memory locations having addresses which indicate the chord type of the pattern. This is the arrangement which has been implemented in the preferred embodiment. More specifically, for each chord type desired to be recognized, a plurality of chord pattern signals representing corresponding key patterns are stored in memory locations having addresses related to that chord type. After the chord pattern signals have been stored, harmony selection system 86 generates a playing key pattern signal identifying the pattern of the playing keys actuated by the performer and also identifying at least one note represented by at least one of the actuated playing keys. The playing key pattern signal then is used in an attempt to locate a corresponding stored chord pattern signal. The chord type signal and root signal are derived from the corresponding chord pattern signal.

The following is a detailed explanation of the preferred form of harmony recognition. As previously explained, harmony selection system 86 produces on conductors 134, a multi-bit representation of the keys of keyboard 88 actuated by a performer. The note represented by an actuated key is represented on one of conductors 134 irrespective of the octave in which it occurs. For example, the C conductor of bus 134 is raised to a logical one state if any one of keys 90, 102, 114 or 126 representing C notes sounded in octaves 1, 2, 3 or 4 respectively, are actuated. Referring to FIG. 15 and 17, the twelve bit representation of the playing key pattern is stored in latch 138 and is transferred by processor 170 into four bit register 224 and eight bit register 226 over bus 152. If microprocessor 170 has a data bus of twelve bits or larger, the playing key pattern signal stored in registers 224 and 226 can be directly compared to the chord pattern signals stored in ROM 164 until a match is found. However, most microprocessors currently available have only an eight bit data bus. It has been discovered that only eight of the bits of the playing key pattern signal need to be compared with the eight bit chord pattern signals stored in memory in order to locate the proper chord type. This is an important feature which enables harmony recognition to be carried out by an eight bit microprocessor with a minimum of memory. The manner in which this unique operation can be achieved by the microprocessor is described in more detail in FIG. 19.

FIG. 19 describes the harmony recognition routine of the program instructions stored in ROM 162. Briefly, the twelve bit playing key pattern signal stored in registers 224, 226 can be reduced to an eight bit representation by judiciously testing certain bits and properly grouping others.

Referring to FIG. 19, in step S10, shift counter 228 and a software error counter are set equal to zero. The playing key pattern signal then is transferred into registers 224 and 226 in step S11. In step S12, the data in the registers is rotated one bit position to the left. Shift counter 228 is then incremented in step S13, and the carry (CY) bit is examined to determine whether it is a logical one or a logical zero in step S14.

If the CY bit is a one, steps S18-S20 (FIG. 19) are used to examine the next three bits of data in order to divide the playing key pattern signal into one of three groups (i.e., group zero, one or two). Assuming the bit representing the first note in the chord is in the CY position, the bit in the MSB position need not be considered since it would represent a note pitched one chromatic step from the note represented in the CY position. No valid chord has this combination of notes. For example, if the player had played keys 90, 94 and 97, the C, E and G lines of conductors 134 would be switched to a logical one state. Assuming the bit representing the C is shifted into the CY position, a logical one bit in the MSB position would indicate that the performer had also played a C.sup..music-sharp.. Since the C, C.sup..music-sharp. combination would represent an invalid chord, the bit in the MSB position can be ignored. For this reason, the data can be rotated two more times in step S18 so that the bit representing a C.sup..music-sharp. in the example is rotated beyond the CY position and ignored. This step then places the bits representing the keys corresponding to notes D and D.sup..music-sharp. in the CY and MSB positions, respectively. If neither the D or D.sup..music-sharp. notes were played by the performer, group zero is selected; if D.sup..music-sharp. but not D was played by the performer, group one is selected; if D but not D.sup..music-sharp. was played by the performer, group two is selected. The group selection process is carried out by steps S19 and S20. If, for example, group zero is selected, the data is rotated one more time in step S21, and a table pointer pointing to the group zero chord pattern signals in the memory is set up in step S22. A search of the group zero chord pattern signals in the memory is conducted in step S23. If a match is found between the remaining eight bits of the key pattern signal and the eight bits of the chord pattern signals stored in group 0, the harmony recognition routine returns to the main program through steps S24 and S25. If no match is found, the data located in registers 224 and 226 during step S14 is restored, and the process is repeated by returning to step S12.

In the event group one is selected, the register data is rotated in step S27, and the routine checks for any special chord pattern signals in step S28. The table pointer then is loaded in step S29, and the previously described search is performed on the group one chord pattern signals in step S23.

In the event group two is selected, the register data again is rotated in step S30, and the routine checks for special chord pattern signals in step S31. The table pointer again is loaded in step S32 and the same type of search is performed on the group two chord pattern signals in step S23.

A better understanding of the unique techniques employed to determine the harmony desired by the performer may be obtained by the following example described in connection with FIGS. 17-19. Referring to FIG. 18, it will be assumed that the performer depresses keys 95, 99 and 102 representing notes F, A and C (thereby indicating that he desires a major chord having the root F). The depression of the keys will result in the playing key pattern signal shown in line A of FIG. 17. The note represented by each bit of the playing key signal is shown by the letters placed below registers 224 and 226 on each of lines A-J in FIG. 17. In accordance with step S12 (FIG. 19), the data is rotated one step to the left as shown in line B (FIG. 17), and shift counter 228 is incremented. After step S18 (FIG. 17), the data takes on the form shown in line C from which the routine determines that group zero should be searched. After step S21, the resulting data is shown in line D of FIG. 17. The table pointer is then loaded and the search performed, but no pattern in group zero corresponds to the pattern shown in line D.

As a result, step S24 is answered in the negative, and the data originally present at step S14 is restored, as shown in line E of FIG. 17. During the data restoration, the LSB bit is incremented to conform with the value of the carry bit CY, so that the data is accurately rotated during subsequent steps. The routine then returns to step S12 which shifts the data as shown in line F of FIG. 17. Since the carry bit, as well as the next three most significant bits, are zero, steps S15-S17 are followed for three additional rotation operations until the data is stored as shown in line G of FIG. 17. After the next shift is performed by step S12, the data is arranged as shown in line H of FIG. 17. Since a logical one is now shifted into the carry position, the routine proceeds through step S18 which rotates the data twice and results in the configuration shown in line I of FIG. 17. Steps S19 and S20 determine that group zero again should be searched, and this procedure is accomplished in steps S21, S22 and S23. Since the eight bit chord pattern illustrated in register 226 at line J is held in ROM 164, the routine detects a match, and returns to the main program through steps S24 and S25.

The chord pattern signal resulting in the match is stored at an address which corresponds to the chord type (major) of the played key pattern (i.e., FAC). The root note is derived from the value of the shift counter according to the following root table:

As shown in line J of FIG. 17, the shift counter value (6) at the time the match occurs corresponds to the root (F) of the chord played by the performer. The chord type signal and root signal are transferred by the processor to other memory locations for use in generating musical segments in a manner described later.

One unique feature of the harmony recognition routine is that the maximum number of searches of the memory is no greater than the number of keys that are depressed by the performer. This unique operation is achieved by steps S14-S17 which continue to shift data until the carry bit (corresponding to a depressed key) is found to be a logical one.

By dividing the chord pattern signals into three groups, only a small number of entries in the memory must be searched for any particular arrangement of data in register 226. These unique features enable the harmony desired by the performer to be selected from a standard keyboard with a minimum of memory and a minimum of processor time.

FIG. 18 illustrates how the data representing any combination of played keys is shifted through registers 224,226. Line A represents the notes and octaves resulting from the playing of the keys aligned with the entries in line A. Line B illustrates the notes initially represented by the bit positions in registers 224,226. Lines C and D illustrate the notes represented by the bit positions of registers 224,226 after 8 and 5 data rotations respectively. With the aid of FIG. 18, those skilled in the art can readily trace the rotation of data representing any combination of played keys.

Referring to FIG. 15, output system 250 comprises identical voice systems 251-256. Each of the voice systems is capable of simulating a separate instrument or voice by which segments of musical accompaniment can be expressed. At any one time, any voice system can sound like any instrument the system is capable of simulating. In other words, the individual voice systems are not confined to a single voice or instrument simulation.

Each of the voice systems can be understood from the following description of system 251. System 251 basically comprises an oscillator circuit 260, a harmonic spectrum adjuster 430, an envelope generator 590 and a modulator 700.

Referring to FIG. 20, oscillator 260 basically comprises an oscillator circuit 261, a selection circuit 285, a portamento module 310, and a vibrato module 400. Oscillator 261 includes a transistor 262, an inductor 264, a diode 265, capacitors 268-272 and resistors 275-277, connected as shown. The signals generated by the oscillator are transmitted to an input of a programmable timer 280 over a conductor 278. The timer can be implemented by Intel Model No. 8253 which is operated in mode 3, the square wave generator mode, and is described in the Intel data catalogue for 1977 at page 10-159. The timer is biased by a resistor 281 and generates square wave pulses on a conductor 282 at a repetition rate determined by the frequency of the oscillator and the interaction between the oscillator and the other modules shown in FIG. 20.

The operation of oscillator circuit 260 is controlled by the data processor over bus 152 under the supervision of selection circuit 285. Selection circuit 285 includes inverters 287-292, NAND gates 294-297, and NOR gates 299-301. Appropriate inverters are connected to gate 297 depending on the precise addressing code used on conductors A2-A7. By transmitting the proper bit pattern over the address bus, either a pitch select line 303 or a portamento select line 304 is raised to a logical one state. In the event the pitch line is selected, timer 280 is enabled to receive information over data bus D0-D7 which determines the repetition rate of the square wave pulses produced on output conductor 282. In the event the portamento line is selected, the portamento module is enabled to receive information over the data bus which controls the pitch and rate of the portamento feature.

Portamento module 310 includes a portamento pitch control circuit 312 comprising an addressable latch 314 which receives information from the data bus. The latch, in turn, controls transistors 316-318 and associated resistors 320-326 which generate a voltage V that determines the upper and lower portamento pitches.

Module 310 also includes a portamento slide up circuit 330 comprising a transistor 332, a capacitor 334 and resistors 335-337 connected as shown. A portamento slide down circuit 340 is also provided by connecting transistors 342,343, a capacitor 345 and resistors 347-350 as shown. The portamento slide up and slide down circuits are controlled by a quad bilateral switch 352 and by inverters 354,355.

Module 310 also includes a portamento rate control circuit 360 comprising an addressable latch 362, resistors 364-365, switching transistors 368-370, resistors 372-378, a one shot multi-vibrator 380 controlled by a timing capacitor 381, and an amplifier circuit comprising transistors 383,384, a capacitor 386, and resistors 388-393. The output of the amplifier circuit is transmitted over a control line 394 to portamento slide up circuit 330.

Vibrato module 400 includes an oscillator 402 containing transistors 404,405, capacitors 407-411, resistors 412-420 and a diode 421, all connected as shown.

Assuming neither the portamento nor vibrato features are used, oscillator 261 generates a signal which is a multiple of the frequency desired for voice system 251. If a lower frequency is desired, a divisor number equal to the divisor required to achieve that lower frequency is transmitted to timer 280 over the data bus. The timer divides the frequency of the input from oscillator 261 by said divisor number in order to produce pulses on conductor 282 having a repetition rate corresponding to the desired frequency or pitch of the note produced by system 251.

Voice system 251 can be instantaneously quieted or silenced by entering the proper data in timer 280 from data bus 154. The timer then enters a non-counting mode which prevents output pulses on conductor 282. This mode of operation is controlled by a QUIET software routine described later.

If a vibrato sound is desired, output D3 of latch S14 is raised to a logical one state by means of the data bus, thereby causing switch 352 to connect conductors 423, 424. As a result of this operation, oscillator 402 is connected with oscillator 261. Oscillator 402 causes the bias on diode 421 to vary periodically, so that the frequency of oscillator 261 is periodically varied.

If the musical segment calls for a portamento slide up to a defined note, outputs D0-D2 of latch 314 are set to values which will cause transistors 316-318 to produce a voltage V corresponding to the starting pitch of the portamento slide. Output D4 of latch 314 then is switched to a state which will cause switch 352 to interconnect voltage V with conductor 338. At the same time, transistor 332 is switched to its conductive state by output D5 of latch 314 and inverter 354, so that capacitor 334 is charged to voltage V. This process increases the control voltage on oscillator 261, thereby decreasing the oscillator frequency to a value established by voltage V. Diode 265 operates as a voltage-sensitive variable impedance which changes the time constant of the oscillator feedback circuit. When the portamento slide is to commence, transistor 332 is switched off through the operation of latch 314, and the voltage across capacitor 334 decreases to its normal value, thereby increasing the frequency of oscillator 261 to its normal value.

In the event that the musical segment calls for a portamento slide down from a defined note to an undefined note, transistors 316-318 again establish a value V that determines the ultimate pitch at the bottom of the slide, and switch 352 enables the voltage V to be connected to conductor 351. At the same time, latch 314 and inverter 354 cause transistor 343 to be switched to its conductive state, so that capacitor 345 is discharged to ground potential, and oscillator 251 operates normally. When the portamento slide down is to commence, the state of inverter 354 is reversed so that transistor 343 turns off and transistor 342 turns on. Capacitor 345 then charges to voltage V, thereby increasing the control voltage on oscillator 261 and causing a decrease in the frequency of its output.

The rate at which the portamento slide up or slide down proceeds is controlled by circuit 360. One shot 380 receives tempo clock pulses from tempo clock 232 through conductor 238, and transforms the tempo clock pulses into constant width pulses. As a result, when the rate of the tempo clock increases, the duty cycle of the pulses from one shot 380 increases. The time constant of one shot 380 is controlled through transistors 368-370 which can be turned on or turned off through latch 362 by means of the data bus. This novel circuitry enables the pulse width of one shot 380 to be programmed.

As the duty cycle of the pulses produced by one shot 380 increases, the average amount of negative voltage applied to conductor 394 per cycle increases. As a result, capacitor 334 discharges and capacitor 345 charges more rapidly, thereby increasing the rate of the portamento slide up or slide down. This is an important feature which automatically increases the rate of the slide as the rate of the tempo clock increases. By using this novel technique, the circuitry automatically speeds up the rate of the portamento slide as the performer speeds up his music. The portamento slide automatically proceeds at a rate appropriate to the desires of the performer as indicated through his setting of knob 234 of the tempo clock.

Referring to FIG. 21, harmonic spectrum adjuster 430 comprises a duty cycle adjusting circuit 432 that includes a flipflop 434 consisting of NAND gates 436,437, a set input 438 and a reset input 439. An operational amplifier 440 having an inverting input 441 and a noninverting input 442 is configured as a balanced comparator 443. The input signal from conductor 282 is differentiated by a capacitor 446 and a resistor 450, and the positive pulse resulting from the differentiation is removed by a diode 444. Additional capacitors 447,448 and resistors 451-455 are connected as shown. Resistors 453,454 have the same value and capacitors 447,448 have the same value in order to provide a balanced comparison by amplifier 440.

The overall operation of the circuit is controlled from a latch 460 through inverters 462,463 and analog gates 464,467. The latch controls the operation of a transistor 465 which is associated with a capacitor 466 and resistors 468-472, connected as shown. Latch 460 is enabled to receive data from data bus 154 by means of a conventional address decode circuit 473 which is controlled through address bus 155.

Referring to FIG. 21A, circuit 432 accepts rectangular wave pulses (such as RW) on input conductor 282 and adjusts the width of the pulses before they are transmitted to an output conductor 474. The input rectangular wave is differentiated by capacitor 446 and resistor 450, and the positive pulse resulting from the differentiation is removed by diode 444. The remaining negative pulse (s) is transmitted to set input 438 which forces the Q output of flipflop 434 to a logical one state at time T2. During time T1-T2, voltage pulse VC1 is integrated by capacitor 448 and resistor 454 to form voltage NI1, thereby forcing the output of opamp 440 to a logical one state. At time T2, voltage Q from the Q output of flipflop 434 begins to be integrated by resistor 453 and capacitor 447 and voltage I1 increases. Also at time T2, voltage NI1 begins to decay because input voltage VC1 has returned to its zero state. At time T4 when the voltage across capacitor 447 equals the voltage across capacitor 448 (i.e., when NI1-I1), the output of opamp 440 is switched to its zero state, thereby resetting flipflop 434 and forcing the Q output to its zero state. The Q output then remains at its zero state until the next negative S pulse is received through capacitor 446.

The width of the resulting output pulse Q on conductor 474 depends upon the time required for the voltage at input 441 to equal the voltage at input 442. The pulse width varies with the repetition rate of the input pulses, but the duty cycle remains constant. The duty cycle, however, can be varied by changing the level of the rectangular wave VC1 through the operation of transistor 465. Transistor 465 clamps the peaks of the input rectangular wave at about 0.6 volts above the voltage of the base of transistor 465. The voltage at the base of transistor 465, in turn, can be controlled in three ways:

1. Latch 460 can be conditioned through data bus 154 to transmit current through either resistor 471 or 472, thereby varying the base voltage.

2. Latch 460 can be conditioned through data bus 154 to open analog gate 467, thereby controlling the base voltage with the output of envelope generator 590. This mode of operation can achieve a "WAH" effect which is useful for simulating some orchestral sounds.

3. Latch 460 can be conditioned through data bus 154 to open analog gate 464, thereby controlling the base voltage with the output of vibrato oscillator 400.

The effect of transistor 465 on the operation of circuit 432 is illustrated by waveforms VC2, Q2, NI2 and I2 in FIG. 21A. Assuming the voltage on the base of transistor 465 is reduced, voltage VC2 is reduced compared to voltage VC1. Voltage N12 then is integrated to a reduced value during time period T1-T2. Since voltage N12 is reduced, it decays to a lower value more quickly than voltage NI1, and NI2=I2 more quickly than NI1=I1. As a result, Q is returned to its zero state at time T3, earlier than time T4, and a narrower output pulse Q2 results. By using the foregoing circuitry, the duty cycle is predictable and is expressed by the formula: Duty %=V1/2V2, where V1=maximum voltage of clamped pulse Vc, and V2=maximum voltage of input pulse RW.

The provision of duty cycle adjusting circuit is an important feature which improves the ability of the system to create different types of orchestral sounds requiring different harmonic spectrums. For example, the circuit provides a 50% duty cycle for a clarinet-type sound, and a 12.5% duty cycle for a string-type sound.

The operation of the duty cycle adjustment circuit is drastically improved by the balanced nature of comparator 443. Absent the balanced comparator feature, changes in the repetition rate of the input pulses would result in changes in the duty cycle of the output pulses. Due to the unique balanced component arrangement of the comparator, the errors due to changes in repetition rate at one of the opamp inputs balances the errors due to changes in repetition rate at the other opamp input, thereby enabling the adjustment of the duty cycle of the output pulses with great accuracy irrespective of the repetition rate of the input pulses.

Referring to FIG. 22, harmonic spectrum adjuster 430 also comprises a programmable filter 480. The filter includes operational amplifiers 482,486, 490 and 494 having inverting inputs 483, 487, 491 and 495, respectively, and non-inverting inputs 484, 488, 492 and 496, respectively. The filter also includes capacitors 498-518, resistors 522-562, latches 566,567, an address decoder 568, open collector gates 570-572 and an output conductor 574, all connected as shown. When enabled by address decoder 568, latch 566 enables one or more of the resistor-capacitor pairs to be connected into the feedback loops of operational amplifiers 482 or 486 in order to provide adjustable filtering of the pulses received on input conductor 474. When enabled by address decoder 568, latch 567 enables one or more of resistors 558-561 to be connected into the output of operational amplifier 490 through gates 570-572 in order to provide variable attenuation of the filtered signals.

Referring to FIG. 23, envelope generator 590 basically comprises an address decoding circuit 592, a parallel-to-parallel converter 614, a counter 616, a time constant circuit 618, a control logic circuit 656 and an output amplifier 678.

The address decoding circuit includes inverters 594-599, NAND gates 602-604 and NOR gates 607-610. The decoding circuit is responsive to signals on the address bus to enable converter 614 or counter 616 to receive information from data bus 154. Converter 614 is a 12-bit wide, open collector latch in which the outputs are grounded or allowed to float under programmed control.

Time constant circuit 618 comprises a timing capacitor 620, diodes 622-633 and resistors 636-654, all connected as shown.

Control logic circuit 656 includes NAND gates 656-661, NOR gates 663-666, an operational amplifier 668 having an inverting input 669 and a non-inverting input 670, and resistors 672-674, all connected as shown.

Output amplifier 678 includes transistors 680,681, resistors 683-685 and an output conductor 687.

Envelope generator 590 produces an output envelope voltage signal of the type shown opposite waveform O in FIG. 24. The envelope includes an attack portion A, a percussive decay portion PD, a sustain portion S, and a release decay portion D. Each of these portions of the envelope can be changed under programmed control.

In order to operate the generator, parameter signals defining the attach, percussive decay, and release decay portions of the envelope and the sustain level are transmitted over the data bus to converter 614. These parameter signals are stored by converter 614 so that the appropriate resistor-diode pairs of time constant circuit 618 produce an envelope of the proper shape. In order to commence operation, the microprocessor addresses circuit 592 which causes the load input of counter 616 to switch to its zero state. At the same time, counter 616 is loaded through data bus 154 with a number proportional to the proper time duration for the envelope being created. When the load input is switched to its zero state, NOR gates 663-665 cause signal A to switch to its one state, thereby commencing the attack portion of the envelope. Waveform A (FIG. 24) enables one or more of diodes 622-625 to charge capacitor 620. As soon as the voltage across capacitor 620 reaches the trigger voltage of the comparator formed by operational amplifier 668 (approximately three volts), the output of the comparator (waveform CO, FIG. 24) switches state, and signals A and D go to their zero states, thereby initiating the percussive decay (PD) portion of the envelope. During the percussive decay portion, current flows from capacitor 620 through one or more of diodes 628-630 until the sustain level S is reached. The sustain level is determined by the value of resistor 648 and the value of one or the other of resistors 643 and 644 which operate under programmed control.

Counter 616 is decremented by tempo clock pulses from conductor 238. When the duration count loaded in counter 616 is decremented to zero, the borrow output of the counter reverts to its zero state, thereby initiating the release decay (D) portion of the envelope. During the release decay portion of the envelope, signal D is switched to its one state and signal SDW is switched to its zero state, enabling current from capacitor 620 to discharge through diode 631 and one or more of resistors 650-653.

Waveform FT (FIG. 24) illustrates the envelope voltage produced by generator 590 when the same parameter signals resulting in waveform O are used, but the rate of the tempo clock is increased. Portions A,PD and D and the sustain level (S) remain the same, but the duration of the sustain time period (defined by signal SDW) is decreased.

Waveform OP (FIG. 24) illustrates the envelope voltage produced by generator 590 for a percussive instrument, such as a banjo. The normal sustain level is ignored, and a percussive release portion PR is generated. The time constant of the PR portion is controlled by the value of resistor 641 or 642.

Referring to FIG. 24A, modulator 700 comprises operational amplifiers 702,703, capacitors 706-709 and resistors 712-723, connected as shown. The modulator modulates the filtered audio signals received from harmonic spectrum adjuster 430 in accordance with the envelope signal received from envelope generator 590 in order to produce one note of a musical accompaniment on an output conductor 725. The not represents one pitch of one instrument or voice. Other pitches and instruments can be represented by additional voice systems 252-256.

The overall musical instrument is controlled by means of a program stored in ROM 162 which is executed by microprocessor 170. When the instrument is turned on, there are several one-time initialization functions which are performed. Various counters, pointers and variables are initialized by a program called INITLZ. A working area in RAM 166 is set up for stack pointers used by various programs, and a means for swapping these pointers is provided. Each of these initialization procedures is described in steps S40-S43 of the flow chart of FIG. 25.

Referring to FIG. 26, the program called Main works on a hilosophy of four levels. The outer level responds to the musical style (e.g., bossa nova, big band, etc.) selected by the performer, and arranges the logic for two complete musical bars. The second or bar level arranges for the output of four beats for a normal bar and three beats for a waltz bar. The third or beat level arranges for the output of twelve tempo clock pulses. The fourth or clock pulse level locates the proper orchestration and instrument data stored in ROM 164, creates the requisite parameter signals, and outputs the parameter signals to the voice systems in order to create the accompaniment sound.

As shown in step S45 of FIG. 26, the Main program first performs a synchronization function which enables the system and tempo clock 232 to use the same clock pulse as a down beat. Main waits in a loop until it detects a down beat condition and then allows continuation of the program. Main then enters an endless loop which is the outer loop for playing the two-bar pattern. The variable BAR is assigned the value 0 in step S46, and the routine BEAT 1 is called in step S47. BEAT 1 plays one bar (three or four beats) which is identified by the contents of the variable BAR. If BAR is assigned the value 0, the first bar is played; if BAR is assigned the value 1, the second bar is played (See steps S48 and S49). The foregoing loop is performed continuously, alternately playing bar 1 and then playing bar 2.

The BEAT 1 routine called by Main is described in the flow charts of FIGS. 27 and 28. Referring to FIG. 27, BEAT 1 determines when chords are recognized (with respect to beats in a bar), determines the response to an invalid chord played by the performer, and determines the response to a change of chords by the player between the two beat phrases. As described earlier, bars are broken into two parts or phrases. The first of the two phrases always includes two beats, that is beat 1 and beat 2. The second phrase always includes beat 3 and will include beat 4 unless a waltz bar is indicated. The musical bars are broken into these multi-beat phrases so that the proper musical phrasing can be incorporated into the musical accompaniment segments. A unique musical accompaniment segment exists for each musical phrase. If the system recognizes a chord type change between an old phrase and a new phrase, a new unique musical accompaniment is played in the new phrase. However, if a chord type is changed between beats within a phrase, a special operation is required to retain the continuity of the musical phrasing. It has been discovered that at these critical times (i.e., when a chord changes between beat 1 and beat 2 or when a chord changes between beat 3 and beat 4), the beat 1 musical accompaniment should be played in place of the beat 2 or beat 4 accompaniment. The musical consequences of this concept can best be explained by reference to FIG. 5.

Referring to section III of FIG. 5, during bar 1, the accompaniment progresses through F6 and Gm7 harmony on beats 1 and 2, respectively, in response to an F maj chord played by the performer. In the event the F maj chord is played immediately prior to beat 1, the progression from F6 to Gm7 sounds like a natural progression to the ear. However, if the F maj chord were not played until immediately prior to beat 2, the sounding of Gm7 harmony by the instrument without first sounding an F6 chord would seem undesirable to most performers. As a result, the instrument replaces the beat 2 harmony (Gm7) with the beat 1 harmony (F6), if an F maj chord is played between beats 1 and 2 of bar 1. A similar replacement occurs for chords changed betweedn beats 3 and 4 of a 4 beat bar. This is a unique feature which enables musical continuity to exist in an instrument capable of executing diverse musical techniques. A more detailed example of these concepts is given in the following Table A:

As an example of how Table A can be interpreted, the orchestration signals corresponding to GM harmony stored for normal usage during bar 1, beat 1 are used during bar 1, beat 2 of the tempo clock due to the change in harmony between beats 1 and 2 of bar 1.

The foregoing concepts are incorporated into the BEAT 1 routine which is shown in the flow charts of FIGS. 27 and 28. During the first beat, the variable BEAT is set to 0 (step 851), and the harmony recognition routine (FIG. 19) is called (step S52) in order to determine the chord type and root desired by the performer. In step S53, the QUIET routine is called to prevent any overhang from a previous musical segment. As previously explained, QUIET enters a number in timer 280 through data bus 154 (FIG. 20) which prevents oscillator 260 from emitting pulses. Overhang may result when a note continues between beats 1 and 2 or between beats 3 and 4. For example, many of the musical segments are written so that notes continue uninterrupted between beats 2 and 3 or between beats 4 and 1. Thus, between these beats, the QUIET routine prevents a conflict between the notes of the old beats and the notes of the new beats. In addition, overhang can result due to a long release decay which extends the envelope generated by generator 590 into the next beat.

If the recognition routine discovers a new chord type or new root, the identification of the new chord type or new root is stored in step S54 by a routine called SAME. The routine determines whether the new chord type and root are the same as the old chord type and root.

After any new chord types or roots have been handled in step S54, the ONE BEAT routine is called in step S55. The ONE BEAT routine arranges for the output of one entire beat (12 tempo clock pulses) and then increments the variable BEAT so that the second beat of the current bar is processed.

During the second beat, the recognition routine again is called in step S56, and any new chord type or root is stored by the SAME routine in step S57. If the chord type and root have not changed between the beats 1 and 2 (i.e., if they are the same), step S58 directs the program to call the ONE BEAT routine (step S61). If the chord type or root has changed, step S58 compels the BEAT variable to return to a 0 value and calls the QUIET routine in steps S59 and S60, so that the musical accompaniment for the first beat will be produced during beat 2. As previously explained, this procedure is necessary when the chord type or root has changed between the beats of a 2 beat phrase.

Referring to FIG. 28, during the third beat of the bar, the variable BEAT is incremented to the value 2 in step S62. Steps S63-S66 then follow the same procedure followed by steps S52-S55, in connection with the first beat (FIG. 27). At step S67, the input downbeat routine (INDB) is called to determine whether the third beat completes a 3 beat waltz phrase or whether a fourth beat is required. If the accompaniment is being played in waltz time, the musical phrase is completed, and the program is returned through steps S68 and S69.

In the event a fourth beat is required, the recognition routine is called in step S70, and any change in chord type or root is detected in step S71. In the event that neither the chord type nor root was changed, step S72 jumps the program to step S75 which calls the ONE BEAT routine. If a new chord type or root was detected in step S73, and the QUIET routine is called in step S74, so that a musical accompaniment for the first beat will be played in step S75. At the conclusion of the fourth beat, the program is returned through step S76.

The ONE BEAT routine called by the BEAT 1 routine (FIGS. 27 and 28) is shown in the flow chart of FIG. 29. In step S79, a variable CLKCNT is set to 0. CLKCNT counts the number of tempo clock pulses and has a value which can vary from 0 to 11, since there are 12 clock pulses in each beat. The OUTPUT routine is called in step S80, and the ONE BEAT routine then waits for a tempo clock transition at step S81. When a clock transition is sensed, the CLKCNT variable is incremented in step S82, and the OUTPUT routine again is called if the end of the beat has not occurred (i.e., if CLKCNT is less than 11). When CLKCNT reaches 11, step S83 causes the variable BEAT to be incremented in step S84, and causes a return to the BEAT 1 routine (FIGS. 27 and 28) in step S85.

The OUTPUT routine called during the ONE BEAT routine is described in FIG. 30. Assuming the beat is 1 or 3 and the tempo clock count is 0 (Steps S89, S90), the root signal obtained by the harmony recognition routine (FIG. 19) is converted to one of the root groups previously identified in step S91. In step S92, a table pointer to the orchestration table in ROM 164 is set up according to the musical style selected by the performer, the bar, the beat, the chord type and the root group.

The organization of the orchestration table in ROM 164 is illustrated in FIG. 31. As shown in that Figure, each musical style selected by the performer, (such as bossa nova) can point to any one of the five different chord types recognized by the harmony recognition routine (i.e., major, minor, diminished, augmented and seventh). In turn, each chord type can point to any one of the four different root groups, and each of the root groups can point to an address identifying any one of four different combinations of beat and bar (i.e., beat 1, bar 1; beat 3, bar 1; beat 1, bar 2; and beat 3, bar 2).

Referring again to FIG. 30, step S93, after the table pointer is set up to point to the proper address, of the orchestration table, six software counter L1-L6 corresponding to the six voice systems 251-256 are set equal to 0. In step S94, a line/time pointer is set to point to counter L1. The software counters L1-L6 determine when a new note needs to be produced by one of voice systems 251-256. If the counter has not been decremented to 0, no new note needs to be produced, and the voice system can be ignored by the microprocessor. However, when one of counter L1-L6 is decremented to 0, orchestration signals must be read from ROM 164 in order to produce the next note. The orchestration signals located in ROM 164 are stored in the form illustrated in the following Table 1, in which an "x" indicates a bit of a word:

Each orchestration table entry consists of two bytes. The first byte comprises (a) a five bit word NO which is related to the pitch of the note to be produced, and (b) a three bit word INST which defines the type of instrument or voice which the note is to simulate. The second byte comprises (a) a four bit word S.D. which defines the duration of the sustain time of the envelope generator (i.e., the duration of signal SDW, FIG. 24) and (b) another four bit word N.E. which defines the rest time until the next note of the voice is produced (i.e., the duration from the termination of one SDW signal to the commencement of the next SDW signal by the same envelope generator). As previously described in connection with FIG. 23, the S.D. word is transmitted to counter 66 in order to generate the proper envelope for the production of the note.

Returning to FIG. 30, if the current L counter is 0, the NO and INST words are read out of the orchestration table in step S96. According to step S97, if the value of the INST word is 0, a musical rest is indicated, and the value N.E. is loaded into the current L counter in step S98. In step S99, the pointer for the L counters is incremented to point to the next counter, and, in step S103, the current L counter is decremented.

Since the OUTPUT routine is executed once during each tempo clock pulse, the L counters are decremented once during each such clock pulse. As a result, the L counters are kept in synchronism with the tempo clock pulses. After all of the L counters have been serviced during a tempo clock pulse, the program returns to the ONE BEAT routine through steps S105 and S106. If all L counters have not been serviced, the routine returns the step S95 and is repeated with respect to the remaining L counters.

Returning to step S97, if the value of the INST word is not equal to 0, a real instrument is indicated, and the instrument routine (INSTRU) is called in step S100. After INSTRU is completed, the orchestration table pointer is moved to the second byte of the orchestration table entry (See Table 1) in step S101. The sum of the sustain duration and rest time (i.e., the sum of words S.D. and N.E.) then is loaded into the current L counter in step S102 in order to define the next time when the voice system corresponding to the current L counter need service. The table pointers then are incremented in step S99, and the routine follows the previously-described steps S103-S106.

Referring to FIG. 32, when the instrument routine (INSTRU) is called, a pointer to the proper entry in the instrument table stored in ROM 164 is calculated from the current value of the line/time pointer (step S94) and from the INST word stored in the orchestration table (Table 1) (step S111). The instrument signals located in ROM 164 are stored in the form illustrated in the following Table 2:

Each entry consists of eight words, and each word has 8 bits. Once the proper entry in the instrument table is addressed by the calculated pointer, a base number BN is read out of word 1 of the entry. BN defines the lowest pitch which can be played by an instrument or voice. In step S112, the microprocessor sums BN+NO (from the orchestration table)+the value of the root (from counter 228, FIG. 17) to obtain a value P. In steps S113 and S114, the value P is used to compute the divisor number which is read out to timer 280 in oscillator 260 on data bus 154. As previously described, the divisor number determines the pitch of the note to be produced by one of voice systems 251-256.

Step S112 is an important feature which enables the INSTRU routine to transpose the divisor number into the proper harmonic key before it is transmitted to a voice system. By using this technique, the orchestration tables can store a single entry for every different key in which the accompaniment ultimately might be played. This technique saves a considerable amount of memory. In step S115, the parameter signals stored as words 2-8 in the instrument table entry are transmitted over bus 154 to the appropriate latches of the proper voice system.

Words 2 and 3 (Table 2) store the parameter signals which define the attack (A), percussive decay (PD), sustain level (S), release decay (D) and percussive release (PR) portions of the envelope signal (signal 0, FIG. 24) produced by envelope generator 590. Each of these signals is transmitted to converter 614 (FIG. 23).

Word 4 stores a pulse width parameter signal which results in the selection of resistors 471 or 472 (FIG. 21), a WAH on signal which controls analog gate 467, and a Vib. Mod. on signal which controls analog gate 646. Each of these signals is transmitted to latch 460 (FIG. 21).

Word 5 stores a volume control parameter signal which controls the operation of open collector gates 570-572 (FIG. 22). This parameter signal is transmitted to latch 567.

Word 6 stores a portamento and vibrato control parameter signal which controls the portamento up-down direction and pitch and also enables vibrato oscillator 400 (FIG. 20). This signal is transmitted to latch 314.

Word 7 stores a portamento rate parameter signal which controls the pulse width of one shot 380 (FIG. 20). This signal is transmitted to latch 362.

Word 8 stores a filter parameter signal which controls the resistor-capacitor combinations connected into programmable filter 480 (FIG. 22). This signal is transmitted to latch 566. Referring again to FIG. 32, in step S116, the value SD is read from the orchestration table into counter 616 of the envelope generator (FIG. 23) in order to determine the sustain time duration of the note. The program then is returned to the output routine through step S117. The parameter signals control the designated voice system so that a tone signal having the proper pitch and harmonic spectrum is generated. The tone signals from each of the voice systems are summed and amplified in amplifier 77 and are converted to sound waves by transducer 79.

The operation of the foregoing system may be more clearly understood from the following example described with reference to FIG. 8. FIG. 8 describes the music desired to be produced when a performer selects the Baroque style and plays a B flat 7th chord on the harmony keyboard. The upper or treble staff to be produced by the instrument is to sound like a harpsichord; the middle staff of music is to sound like brass and the lower staff of music is to sound like a string instrument. In order to achieve this result, the notes written on the upper staff can be produced by voice system 251, the notes indicated on the middle staff of music can be produced by voice system 252 and the notes indicated on the lower staff of music can be produced by voice system 253 (FIG. 15). Of course, any other of the 6 voice systems could be assigned to the respective lines of music and still achieve the same results. As indicated by FIG. 31, there are a number of memory locations which are assigned to the Baroque style, 7th chord type, root group 3, BEAT 1, BAR 1 of the music described in FIG. 8. In order to produce the notes shown in BAR 1, BEAT 1 of FIG. 8, the locations of the orchestration table for BAR 1 BEAT 1 are filled in ascending numerical order. The order corresponds to the time sequence of the notes.

For example, the first four table entries would contain information for rest R and notes N1-N3, respectively shown in FIG. 8.

Referring to Table 1, the first entry (i.e., the entry for rest R, FIG. 8) would contain a word INST having a value 000, indicating that a rest is desired. The second byte of the entry would contain a word N.E. having a value defining the musical time duration of rest R.

Referring to Table 1, the second entry would contain a word NO which when added to the base number BN for the harpsichord voice and the value of the root (B flat) would result in a number P. P, in turn, is used to calculate the divisor number which is read out to timer 280 and oscillator 260 in order to produce rectangular wave pulses having a repetition rate corresponding to the fundamental pitch of note N1.

The second entry also contains a word INST which identifies the brass voice and a word SD which dictates that note N1 will be produced for a time period appropriate to a quarter note. Word NE will have a zero value because there is no rest between note N1 and the next note in the brass voice, note N5.

The orchestration table entries for notes N2-N6 are stored in a similar manner. Of course, the table entries for notes N2-N6 contain different values in order to make these notes sound in different voices and for periods of time appropriate to their music time values.

Three different instrument table entries (Table 2) are stored, one for each of the three different voices of notes N1-N3.

Referring to FIGS. 8 and 30, when the program enters the output routine due to the performer playing a B flat 7 chord in the Baroque style at the beginning of a measure, since the BEAT is 1 and the CLKCNT is zero (steps S89, S90), the root signal is converted to root group 3 in step S91 and the orchestration table pointer is set to address the first entry described above corresponding to rest R.

Counters L1-L6 are set to 0 (step S93) and the line time (L/T) pointer points to counter L1 (step S94). Since counter L1 is set to zero, words NO and INST are extracted from the first memory entry (Step S96). Since the value of INST is 0, the value of N.E. is loaded into counter L1 (steps S97, S98). The table pointer is incremented to point to the second entry (corresponding to note N1). The L1 counter then is decremented by 1 (step S103), and the L/T pointer is incremented in order to point to counter L2 (step S104). Since the L/T pointer is less than 6, the output routine returns to step S95 in order to determine the value of counter L2.

Since counter L2 is set to 0, the instrument routine is called (steps S97, S100). In the manner previously described, the instrument routine causes the proper entries from the instrument table (Table 2) to be outputted to output system 252 so that note N1 is produced in the brass voice for the time value of a quarter note.

The program then returns to step S101 of the output routine in which the table pointer is incremented to point at the second byte of the orchestration table entry for note N1. (Table 1). The sustain duration (SD) and the rest time (NE) values in the second byte are then summed in order to determine the overall time period from the commencement of note N1 to the commencement of note N5. The value of this time period is loaded into the L2 counter (step S102), and the table pointer is incremented to point to the third entry corresponding to note N2 (step S99). The L2 counter is then decremented by 1 (step S103), and the LT pointer is incremented in order to point to counter L3 (step S104). Since the L/T pointer is less than 6, the output routine returns to step /S95 in order to determine the value of counter L3.

Since the value of counter L3 is zero, the NO and INST words corresponding to note N2 are extracted from the orchestration table (step S96). Since the value of INST indicates the string voice, the instrument routine is called (steps S97 and S100). The instrument routine operates in the foregoing manner in order to produce note N2 through output systems 253. The program then returns to step S101 where the second byte of the orchestration table entry for note N2 is analyzed. The sustain duration and rest time for note N2 are summed and placed into counter L3 to define a time period from the beginning of note N2 until the beginning of the next note in the string voice, note N6. Of course, the summed value for N2 is the same as the summed value for note N1, since both N1 and N2 are quarter notes and must extend over one full musical beat. The table pointer then is incremented to point to the fourth entry in step S99. Counter L2 is decremented in step S103 and L/T pointer is incremented in step S104 to point to counter L4. The program then returns through steps S105 and S95 to examine counter L4.

Since the value of counter L4 is zero, the NO and INST words from the fourth orchestration table entry are extracted. Since only three different voices are used in the Baroque style, the capacity of the system for three additional voices is not needed. As a result, the fourth, fifth and sixth orchestration table entries corresponding to counters L4, L5, and L6 each have their INST values set equal to zero. As a result, in step S98, the NE duration corresponding to the entire two measure musical segment shown in FIG. 8 is loaded in counter L4, and the instrument routine is not called. As a result, no sound is produced in response to the fourth orchestration table entry. The table pointer is then incremented to point to the fifth orchestration table entry (step S99) and the L4 counter is decremented (step S103). The L/T pointer is then incremented to point to the L5 counter which is then evaluated (steps S105, S95). The L5 and L6 counters are handled in the same way as the L4 counter so that no sound results from the fifth and sixth orchestration table entries. As a result, after the L6 counter has been evaluated, the program is returned to step 581 of the ONE BEAT routine (FIG. 29).

In summary, during the first cycle of operation of the output routine, rest R and notes N1-N2 are commenced, and their durations are defined by the values loaded into software counters L1-L3. In addition, the other three voices corresponding to counters L4-L6 are quieted and their duration is extended throughout the two measure musical cycle shown in FIG. 8. The initial cycle of operation of the output routine is carried out so rapidly that notes N1-N2 appear to sound at the same time.

Referring to FIG. 29, as soon as the CLKCNT is incremented to 1, (step S82), the output routine again is called (step S80). Since the CLKCNT is no longer at zero, the output routine proceeds directly to step S94 where the L/T pointer again points to counter L1. Since counter L1 is not yet zero, the output routine proceeds directly to step S103 where counter L1 is decremented and the L/T pointer is incremented to point counter L2. Since none of counters L1-L6 have yet been decremented to zero, the orchestration table does not need to be consulted for any of the counters and the output routine is again returned to step S81 of the 1 BEAT routine (step S106).

The foregoing procedure is followed until the CLKCNT (FIG. 29) advances to 5, thereby indicating that BEAT 1 is half completed. At this point in time, rest R (FIG. 8) should terminate and note N3 should begin sounding. After the CLKCNT advances to 5 and the output routine is called in step S80, the output routine immediately advances to step S94 and the L/T pointer is set to counter L1.

Since counter L1 has been decremented to zero by the previous cycles of the output routine during CLKCNTS 0-4, the NO and INST words corresponding to note N3 are extracted from the seventh orchestration table entry (step S96). Since the value of the INST word indicates a harpsichord voice, the instrument routine is called in step S100. In the manner described above, the instrument routine causes note N3 to sound through output system 251. The program then returns to step S101 of the output routine where the orchestration table pointer is incremented to point to the second byte which contains the SD and NE values for note N3. These values are summed in order to determine a time period from the beginning of note N4 to the beginning of the next note in the harpsichord voice, note N4. This value is loaded into counter L1 and the orchestration table pointer is incremented to point to the eighth orchestration table entry (step S99). Counter L1 is then decremented (step S103), and the L/T pointer is incremented to point to counter L2 (step S104).

Since the value of counter L2 is not yet zero, (since it corresponds to note N1 which is held for one full musical beat), the output routine proceeds directly to step S103 where the L2 counter value is decremented. The same procedure is followed for counters L3-L6 during CLKCNT 5 until the program returns to the ONE BEAT routine through step S106. The ONE BEAT routine will continue to call the output routine for CLKCNTS 6-11. However, since no additional notes need to be originated during BEAT 1 of BAR 1 (FIG. 8), the orchestration table entries never need to be consulted.

At the end of BEAT 1, the program returns to the BEAT 1 routine through step S85 (FIGS. 27, 28). At the beginning of the second beat, the ONE BEAT routine is called in step S55, and the same procedure is followed. That is, during CLKCNT 0 of the second beat, notes N4, N5 and N6 are originated and note N3 is terminated. As a result, each of the notes shown in FIG. 8 is played in its exact musical voice, pitch and time value as long as the performer continues to play a B flat 7th chord.

Those skilled in the art will recognize that each of the musical features set forth in the Musical Organization and Capablities section of the specification can be implemented by choosing the proper values for the orchestration and instrument table entries and by placing the entries in an appropriate order in the memory so that they are available for access when the desired musical notes need to be generated.

A detailed program listing suitable for executing the flow charts of FIGS. 19, 25-30 and 32, as well as exemplary entries for the orchestration and instrument tables follows. The listings named STYLE and MAOXXX correspond to the orchestration table, and the listing named INSTBL corresponds to the instrumentation table.

Those skilled in the art will recognize that the preferred embodiment may be altered and modified without departing from the true spirit and scope of the invention as defined in the appended claims. ##SPC1## ##SPC2## ##SPC3## ##SPC4##