Digital High Speed Guitar Synthesizer

BACKGROUND OF THE INVENTION

Field

This invention relates to musical instruments and specifically to electronic instruments which synthesize musical tones. It provides such an instrument which may be embodied either as a monophonic device or as a polyphonic device capable of synthesizing chords, after the fashion of a guitar.

State of the Art

Guitars have been popular musical instruments for centuries. In a guitar, tones are generated by plucking or strumming one or more strings. The tones thus produced include a number of harmonics which are selectively amplified by the sound box of the instrument. In recent decades, electronic pickups have been incorporated in certain guitars and associated electronic circuitry has been employed to select, amplify and/or modify the tones generated by the guitar strings. In many modern electric guitars, the sound box has been replaced by a solid structural member because the treatment of the tones generated by the string is entirely electronic. The guitar has long been recognized as an extremely versatile instrument in that it is capable of playing chords and melody lines. Moreover, it is by virtue of its configuration and the technique of playing the instrument, a relatively simple instrument to learn. In addition, the fashion in which a guitar is customarily held by a player lends a degree of personal intimacy between the instrument and the performer which cannot be duplicated, and is normally not associated with keyboard instruments.

Electronic musical synthesizers of various types are also well known. Although such instruments are widely used in recording studios and for certain types of concert effects, they are severely limited and do not lend themselves well to virtuoso solo performances. Such instruments are interesting and useful because tones are generated entirely electronically, and they do not rely upon a vibrating string for this purpose. Aesthetically, however, they lack the warmth of traditional instruments such as guitars. Moreover, as presently available, they are monophonic or at most diaphonic, and are thus not capable of producing chords. The only practical way to produce polyphonic music with such instruments is to either use a plurality of them or to record monophonic lines in sequence on several tracks in a studio, and to thereafter blend the tracks into a polyphonic summation.

A number of United States patents disclose electronically operated stringed instruments. For example, U.S. Pat. No. 3,465,086 (Borell) and 3,709,084 (stobough) are typical of patents disclosing electronic circuits for either amplification or tone generation. U.S. Pat. No. 2,792,738 (Donahue) discloses a guitar in which tones are produced by depressing rather than plucking the strings. U.S. Pat. No. 3,555,166 (Gasser) discloses an electronic guitar having keys located on its neck which, when depressed, actuate switches. The body of the guitar includes an accordion-type keyboard, the keys of which also actuate switches. U.S. Pat. No. 3,666,875 (Ranzato) discloses an electronically operated device for simulating stringed instruments. The tones of this device are generated upon release of switches or buttons on the body of the guitar. U.S. Pat. No. 3,662,641 (Allen) discloses the use of touch sensitive switches located on the neck of a guitar. Tones are generated by plucking a special type of short string. None of the aforementioned patents discloses an instrument which can be played in the fashion of a guitar, that is, by supporting the neck of the guitar in the palm of the hand while moving between fret and string locations to quickly produce tones of the desired pitch. Moreover, none of these patents disclose an instrument which is capable of producing electronically generated chords.

The present invention provides a musical instrument having the appearance and characteristics of a guitar; that is, it is held and played in the fashion of a guitar so that one familiar with the technique of playing an electric guitar can readily adapt to the instrument of this invention. However, the sound generated by the instrument is produced entirely electronically. The sounds are generated through techniques similar to those currently employed to produce electronically synthesized sounds, but the instrument processes the sounds in novel ways to produce a variety of interesting musical effects.

The invention can be embodied variously as either a monophonic instrument or a polyphonic instrument. In either case it can be provided with a wide range of capabilities, and can produce sounds and effects analogous to those available with acoustic and electric guitars. Additional unique effects and tones may be incorporated in the instrument of this invention if desired. As typically embodied, the invention comprises four basic functional elements, namely, a touch arm apparatus, a strum simulation apparatus, means for envelope generation (volume or loudness), and means for harmonic generation (both static and time variable).

An important aspect of the present invention is the configuration of the guitar arm; i.e., the touch arm apparatus. The arm includes structures corresponding to conventional frets. These frets or segments of these frets comprise one contact of a touch-sensitive switch. The other contact of each such switch is connected to a conductive strip positioned along the arm for continuous contact by the palm of a player's hand, when the guitar is held in a conventional fashion. The fret contacts are located at "addresses" which correspond to the intersection points of strings and frets on a traditional guitar. Each address may thus be identified by a "file" or string designation and a "rank" or fret designation.

Preferably, the touch switches are of common design and are constructed from high impedance (complimentary metal oxide semiconductor CMOS) devices. According to some forms of the invention, the back of the instrument is constructed of a lightweight metal electrically connected to a voltage potential so that it is coupled through the user's hand with the frets. The hand acts as a high impedance resistor between the guitar arm and the frets. The fret board portion of the instrument may also include charged sections to increase touch switching sensitivity. Of course, care should be taken in the construction of such embodiments to avoid the hazards of electrical shock (although this possibility is very minimal considering the low current of CMOS devices). Nevertheless, instruments of this type will find application in the controlled environment of a recording studio. Preferably, a unique gating system is associated with the touch switches to sense when two or more switches in the same string file are activated. The gating system functions such that only the pressed fret position (rank) closest to the body of the guitar selects a tone from the tones available for that string. This feature assures that tone selection for any string is entirely analogous to that experienced with a conventional guitar.

The strum area of the guitar of this invention is also unique. It comprises switch mechanisms which are configurated for actuation as though they were strings, that is, a plucking, strumming or tapping action will suffice to bring individual strum switches into operation. Generally, a plurality of conductive members (such as wires or bars) are mounted across the strum area to simulate strings corresponding in number and location to the strings which would be present in a conventional bass or lead guitar. These switches may also be touch-sensitive or they may be mechanically adapted for operation through the physical touching of contact elements. In any event, actuation of a strum switch generates a tone which is associated with all of the fret locations (addresses) intersected by an imaginary string associated with that strum switch. The pitch of the tone generated by activation of any strum which is determined by activating any of the fret switches associated with that strum switch just as in the case of an ordinary guitar.

In the drawings, which illustrate that which is presently regarded as the best mode for carrying out the invention:

FIG. 1 is a plan view of a guitar instrument of this invention, showing its face or playing surface;

FIGS. 2a and 2b are fragmentary views, partially in section, showing a portion of the arm of the guitar of FIG. 1 designated by the reference line 2--2 of FIG. 1 and illustrating alternative fret constructions;

FIGS. 3a and 3b are alternative cross-sectional views taken along the reference line 3--3 of FIG. 1 illustrating the fret constructions of FIGS. 2a and 2b, respectively, rotated 90.degree.;

FIG. 4a is an electronic diagram illustrating the circuit components of a touch-sensitive switch device of this invention;

FIG. 4b is a diagram similar to FIG. 4a illustrating a similar touch-sensitive switch adapted for the strum area of the instrument of FIG. 1;

FIG. 4c is an electronic diagram illustrating an alternative circuit for use in place of those illustrated by FIGS. 4a and 4b;

FIG. 5 illustrates a strum bar portion of the strum area and shows a mechanical equivalent of the touch-sensitive circuit illustrated by FIG. 4b;

FIG. 6 is a fragmentary view in cross-section taken along the reference line 6--6 of FIG. 6;

FIG. 7 illustrates an alternative construction of the strum area which relies upon direct physical grounding contact rather than touch-sensitive switching;

FIG. 8 is a block diagram illustrating the basic circuit functions and organization of a monophonic system embodying the invention;

FIG. 9 is a fragmentary view of a portion of the instrument illustrated by FIG. 1;

FIG. 10 is an electronic block diagram similar to FIG. 8 illustrating an alternative monophonic system embodying the invention;

FIG. 11 is a block diagram showing the circuit configuration and components for a polyphonic system embodying the invention;

FIG. 12 is a partial diagram illustrating a fret selection multiplexer useful in connection with the monophonic embodiment illustrated by FIG. 8;

FIG. 13 is a schematic circuit diagram illustrating the components of a priority selector useful with both monophonic and polyphonic embodiments of the invention;

FIG. 14 is a logic table illustrating the output condition resulting from the input condition of the gates of FIG. 13;

FIG. 15 is a schematic diagram illustrating the components of a string selector circuit useful in connection with monophonic embodiments of the invention;

FIG. 16 is a schematic diagram illustrating the circuit components of a pitch matrix digital to analog circuit of the invention;

FIG. 17 is a frequency matrix table illustrating the pitch ratio resulting from the various fret locations of the guitar arm of FIG. 1;

FIG. 18 is a schematic circuit diagram illustrating the components of an oscillator and wave shape selection circuit of the invention;

FIG. 19 is a schematic circuit diagram illustrating the components of an envelope generator circuit of the invention;

FIG. 20 is a schematic circuit diagram illustrating the practical components of a filter circuit of this invention;

FIG. 21 is a schematic diagram illustrating the practical components of a low frequency oscillator circuit of this invention referred to in certain other figures as FL01;

FIG. 22 is a schematic diagram illustrating practical components of a second low frequency oscillator circuit of this invention referred to in certain other figures as LF02;

FIG. 23 is a schematic circuit diagram illustrating practical components of a pitch bend control circuit of this invention;

FIG. 24 is a schematic circuit diagram illustrating the practical components of a frequency modulation vibrato control circuit of this invention; and

FIG. 25 is a schematic circuit diagram illustrating practical components of a volume voltage control amplifier for volume control of this invention.

The drawings illustrate three distinct embodiments of the invention; namely, two monophonic systems (shown schematically by FIGS. 8 and 10, respectively) and a polyphonic system (shown schematically by FIG. 11). These and other embodiments of the invention will be selected depending upon the performance mode intended for the instrument, among other factors. In any event, FIG. 1 illustrates an arrangement of parts, designated generally 40, with which any of the illustrated embodiments may be incorporated. The instrument 40 is structured in a format similar to a standard electric guitar with a body 41 supporting a strum region 42 and connected to an arm 43 divided by a plurality, typically 15, of frets 44.

In the illustrated instance, the strum region 42 includes a number of strum bars 50 corresponding in placement to the six strings normally found in a six string guitar. It should be understood that embodiments are within contemplation which rely upon a single strumming apparatus 50 or a plurality other than the six illustrated. A plurality of touch-sensitive devices 51 is arranged in a grid of addresses corresponding to the intersection regions of a plurality of ranks of fret locations and files of string locations such that each address (location of a device 51) corresponds to the intersection of a string with a fret by analogy to a conventional guitar. As illustrated, the string locations are extensions of the strum bars 50 up the arm 43 of the instrument. Embodiments are within contemplation in which all of the devices 51 associated with a particular fret 44 are either conductively connected or replaced by a single conductive plate.

As best seen from FIGS. 2 and 3, a conductive strip 55 is carried by the arm 43 arranged for contact with the palm of a hand of an individual holding the arm in the fashion characteristic of a guitar player intending to press strings against selected frets. In the illustrated instance, the conductive element 55 comprises the entire back surface of the arm 43. The touch-sensitive devices 51 are electrically isolated from the conductive element 55 by insulating material 60 which comprises the major portion of the face 61 of the arm 43. The embodiment 62 of the devices 51 illustrated by FIGS. 2a and 3a comprises conductive loops which rise above the surface 61 of the arm 43. The embodiment 64 of the devices 51 illustrated by FIGS. 3a and 3b comprises metallic elements 65 mounted with their upper surfaces approximately flush with the insulating material 60. A cable 66 of individual strands 67 of wires is run in association with the metal elements 65 as best shown by FIG. 2b. Referring to FIGS. 2a and 3a, electronic components 68 may be housed within the arm 43, and the interior of the arm 43 may serve as a conduit for wiring as shown. A section of the top surface of the guitar body, designated generally 80, is devoted to various circuit controls as will be explained in more detail hereinafter.

FIGS. 4 illustrate typical touch switches constructed from high impedance CMOS gates 82. FIG. 4a illustrates such a switch adapted to the fret board 60, wherein the switch 81 incorporates the metallic element 55 as one contact and the touch-responsive device 51 as its other contact. In practice, these contacts are closed by simultaneous contact with the hand of an individual. As illustrated, bringing the input 83 of the gate 82 to low (usually ground) potential triggers the circuit. FIG. 4b illustrates a substantially identical trigger circuit adapted to incorporate a strum bar 50 rather than the device 51 as one of the contacts of the switch 81. While some form of a touch-responsive switch such as illustrated by FIG. 4a is an important feature of this invention, the corresponding switch illustrated by FIG. 4b is regarded as optional. The presently preferred embodiments of the invention substitute a mechanical switch mechanism for the touch-responsive circuit illustrated.

FIGS. 5 and 6 illustrate one embodiment of such a mechanical strumming switch and FIG. 7 illustrates a highly preferred alternative embodiment of such a mechanical strumming switch. The manner in which the mechanical devices may be substituted for the touch-responsive devices into the circuit illustrated by FIG. 4b will be apparent by noting the locations of the signal output 85 in FIGS. 4b, 5 and 7, respectively. FIG. 6 illustrates one manner in which a strum device 50 may be electrically isolated from grounded structure 90 until a spring 91 is moved by finger pressure to bring some portion of the device 50 into contact with the grounded structure 90. A similar arrangement is shown by FIG. 7 in which the block 92 is at ground potential, and individual strumming elements 93 are anchored at one end 94 through bores 95 as shown by FIG. 6 in electrical isolation. Individual conductors (springs 91) are thus suspended through a conductor held at reference potential. The opposite ends of the strings 93 are anchored to an insulator block 96 as shown by FIG. 7 with individual outputs 85 similarly electrically isolated. A notable advantage of the structure illustrated by FIG. 7 is that the output 85 is brought to reference potential by contact of the spring 91 with any portion of the perimeter of the bore 97. Accordingly, a player need not be particularly concerned with the direction he moves his fingers in strumming the instrument. In this respect, the claimed instrument may be less demanding than a conventional guitar.

FIG. 11 illustrates the circuitry associated with each strum switch in a polyphonic system. Thus, each strum switch is connected in circuit with its own tone-generating means so that a plurality of tones may be generated simultaneously by operation of a corresponding plurality of strum switches. As shown, the VCA outputs generated by the several strum switches are fed through a mixer to an amplifier.

The remaining figures are self-explanatory and disclose practical circuits which are associated with the novel touch-sensitive arm structures and strum structures described. These circuits may be controlled in part by knobs and switches within the area 80 of the top face of the instrument (FIG. 1) devoted to controls or by auxiliary foot pedals or control panels. In any event, they are operable to control such effects as pitch bend, resonance, cutoff frequency, volume, attack, decay, sustain vibrato, wave forms, and frequency. Effects associated with a conventional electric guitar; i.e., "bend," "hammer," "pull off," "slide" and "mute" (or release) are readily duplicated with the circuits illustrated. In addition, the illustrated circuits can provide for "infinite sustain," an effect not associated with conventional guitars.

FIG. 18 illustrates a three octave switching capability which is regarded as novel for bass instruments. The midrange is normal pitch with higher and lower octaves derived digitally (see FIG. 17). FIG. 18 also illustrates a practical circuit for wave shape generation and selection. It should be understood that other equivalent circuits are within contemplation.

Although this disclosure makes reference to details of certain illustrated embodiments, and includes specific details of practical circuits, it is not intended thereby to restrict the scope of the claims which themselves recite those details regarded as essential to the invention.