Electronic Piano Circuit Arrangement

This invention relates generally to electronic musical instruments, and more particularly to an electronic piano circuit arrangement which combines a plurality of different signals to obtain the desired tone quality to a piano note. More specifically, the invention is directed to a circuit arrangement which enables combining a multitude of different frequencies in a simple and efficient manner to obtain the desired piano note quality characteristics.

Heretofore, the reproduction of piano sounds by electronic means has been, at best, a first order approximation of the frequency and its associated harmonics. Through extensive research over the years it has been discovered that the actual quality of a piano note, as perceived by listeners, is a combination of factors such as the fundamental frequency, the attack characteristic, the decay characteristic, the harmonics and the combination of other unrelated frequencies. By experimentation it has been determined that by adding the proper amplitudes of harmonics and other frequencies to the fundamental frequency, a more accurate electronic reproduction of an actual piano note can be made. By varying the amplitude of the various signals to be combined, one can produce a piano note quality which is virtually undetectable from that of a real piano tone. This information was set forth in The Journal of the Acoustical Society of America, Volume 34, Number 6, in June of 1962.

In the past, the production of such high quality electronic piano tones has been a very expensive and difficult procedure in that it required large numbers of oscillators and variable amplitude control circuits to insure the proper combination of amplitude signals. This prior art approach was very impractical and required enormous expense and time to produce a piano of the electronic type having the desired tone quality characteristics.

Accordingly, it is an object of this invention to provide a new and improved circuit arrangement whereby an electronic piano tone characteristic can be obtained by combining various amplitudes of harmonics and other signals with the fundamental frequency in an efficient circuit arrangement which is relatively simple and inexpensive to manufacture.

Briefly, the electronic musical circuit arrangement disclosed herein incorporates an X-Y matrix array which utilizes a diode-resistance, series-connected circuit at selected ones of a plurality of crossover points of the matrix. The value of the resistance at each of the crossover points is preselected to introduce into the output line a specific predetermined amplitude of either harmonics or other unrelated frequencies with that of the fundamental frequency so that the tone quality characteristic thereof is more accurately that of an actual piano tone. The resistance value at each of the crossover points may be formed internally with a diode element or may be a discrete resistance element connected in series therewith. The entire matrix array may be formed by large scale integration.

Many other objects, features and advantages of this invention will be more fully realized and understood from the following detailed description when taken in conjunction with the accompanying drawings wherein like reference numerals throughout the various views of the drawings are intended to designate similar elements or components.

FIG. 1 is a block diagram illustrating the overall general concepts of an electronic piano constructed in accordance with the principles of this invention;

FIG. 2 is a fragmentary circuit arrangement of an X-Y matrix array showing the diode connection at selected crossover points for mixing together desired frequencies at predetermined amplitudes to obtain the desired tone quality; and

FIG. 3 is a fragmentary circuit arrangement illustrating a diode-resistor series connection at selected ones of the crossover points.

Referring now to FIG. 1, a block diagram of an electronic piano constructed in accordance with the principles of this invention is shown and designated generally by reference numeral 10. The electronic circuit arrangement 10 includes a multifrequency generator 11, which may be operated from a clock frequency oscillator in the order of about 500 KHz. The output of the multifrequency generator 11 is a plurality of different frequencies which may correspond to the third octave above middle C. These fundamental frequencies are then delivered to a divider bank circuit arrangement 12 to be divided and thereby produce the corresponding lower frequency octaves as well as the desired harmonics.

Most advantageously, the divider bank 12 is delivered through a diode adder circuit arrangement 13 to a pulse and sustain keyer circuit 14. The diode adder circuit 13 includes impedance elements which allow adding together the desired amplitude of predetermined frequencies so that the tone quality of the electronic piano is substantially that of an actual piano. The pulse and sustain keyer circuit 14 produces the attack, decay and sustain characteristics of an actual piano note, as indicated by the waveform curve 16. This output signal is delivered through appropriate filter circuits indicated generally by reference numeral 17 and therefrom to an amplifier and output circuit arrangement 18. The entire circuit arrangement 10 is operated from a power supply 19 which applies suitable operating voltage to all of the stages of the circuit arrangement.

FIG. 2 illustrates a fragmentary portion of the diode adder circuit 13 and only a fragmentary portion of the keyer actuating lines associated therewith. By way of example, the lowest octave of the piano keyboard, that being the third octave below middle C, is illustrated herein. A plurality of lines 20 are connected to suitable keyer circuits 14a which activate the transfer of frequency signals at a plurality of lines 21. The signal on selected ones of the lines 21 is then transferred through the diode resistance arrangement as indicated generally by reference numeral 22 so that a gating action occurs. This will transfer the appropriate frequencies to the output side 23 of the lines 21 so that they can be delivered to the pulse and sustain keyer circuit, filter circuit and amplifier and output circuits. For example, the F'" note will transfer frequencies 43.65, 87.3, 130.8, 174.6, 220.0, 261.6, 311.1, 349.2, 392.0, 440.0, 523.0 and 830.0 to the output line 23a whenever the low F key is actuated. The specific amplitude of each of the notes combined herein is determined by the amount of resistance connected in series with the diode at the crossover point of the matrix array.

This is best illustrated in FIG. 3 which illustrates a diode-resistance network 22a having circuit points 26 and 27 connected to the keyer lines 20 and frequency input line 21, respectively. Here a discrete diode element 28 is connected in series with a discrete resistance element 29 of a predetermined selected value so that the amplitude of the signal being combined is selected to produce the note quality.

What has been described is a simple and efficient diode resistor matrix array which enables combining frequencies of various amplitudes, both harmonic and non-related frequencies, to obtain electronically the piano tone qualities of an actual piano. Variations and modifications of this invention may be effected without departing from the spirit and scope of the novel concepts disclosed and claimed herein.