US3647928A - Electrical musical instrument with ensemble and chief effects and unequal stereophonic outputs - Google Patents

Abstract

An electrical musical instrument for simulating pipe organs, and having a natural ensemble effect, spatial tone-distribution effect, air turbulence effect, wind-pressure-change effect, tracker-keying effect, piano voice keying effect, and exact differently modulated harmonic pitch registers for mutation and compound stops and chiff. These effects are achieved by modulator units coupled between harmonic filtered, tone frequency current sources and a stereophonic amplifier-speaker system which produces outputs having levels of amplitudes which vary differently with respect to each other. The outputs connected to the two speakers have inequalities in amplitudes so that each tone has its own distinctive spatial location. The modulator units comprise insulated gate field-effect transistors which are utilized to modulate the tone frequency currents with different patterns of subsonic frequencies including those producing the simulation of natural air turbulence and wind pressure change. Insulated gate field-effect transistors are also used for switching tone and chiff frequency currents so that the change in amplitude is sigmoid during turn-on and turnoff. RC circuitry in combination with the switching insulated gate field-effect transistors permit tracker keying and piano voice keying.

Description

United States Patent Turner Mar. 7, 1972 [54] ELECTRICAL MUSICAL INSTRUMENT WITH ENSEMBLE AND CHIEF OTHER PUBLICATIONS Herman Burstein, Columbia Stereo Disc System, Elec- EFFECTS AND UNEQUAL tronic Technician, May, 1968, pp. 52- 53. STEREOPHONIC OUTPUTS Primary Examiner-Milton O. Hirshfield [72] Inventor: Wilham D. Turner, 108 Manchester Assistant Examine,. stanley J witkowski Avenue, Moylan, 19065 Attorney-Woodcock, Phelan & Washburn [22] Filed: Mar. 16, 1970 ABSTRACT Appl l964l An electrical musical instrument for simulating pipe organs, Rehted Applicafion Data and having a natural ensemble effect, spatial tone-distribution effect, air turbulence effect, wind-pressure-change effect, 1 Commuatlon-m-part of 18, tracker-keying effect, piano voice keying effect, and exact dif- 1963, abandonedferently modulated harmonic pitch registers for mutation and compound stops and chiff. These effects are achieved by [52] U-S-CI ..84/l.24,84/DIGl4,84/DIG.5, modulator units coupled between harmonic filtered, tone 8 /Dl 27 frequency current sources and a stereophonic amplifier- [51] Int. Cl ..Gl0h -l/02,Gl0h 1/04 speaker system which produces outputs having levels of am- [58] Field of Search ..84/ l .-l l-l 1 3, 1.19-1.22, plitudes which vary differently with respect to each other. The 84/ 1.24-1.27, DIG. l5, DIG. 4, DIG. 5, DIG. 27 outputs connected to the two speakers have inequalities in amplitudes so that each tone has its own distinctive spatial lo- {561 References Cited cation. The modulator units comprise insulated gate field-effect transistors which are utilized to modulate the tone UNITED STATES PATENTS frequency currents with different patterns of subsonic frequencies including those producing the simulation of natu- 23 ral air turbulence and wind pressure change. Insulated gate 3007361 11/1961 Wayne field-effect transistors are also used for switching tone and ayne chiff frequency currents'so that the change in amplitude is sig- 3'l47333 9/1964 Wayne ll moid during tum-on and turnoff. RC circuitry in combination 3255'297 6/1966 "84/125 with the switching insulated gate field-effect transistors permit 3,450,825 6/1969 Cunningham... ..84/1.24 Hacker y g and piano voice y g 3,467,759 9/1969 Campbell ..84/ 1.25 3,493,669 2/1970 Elbrecht et a1 ..84/1.25 X 21 Claims, 37 Drawing Figures I 201 f 226 252 203 S l 206 209 214 220 r21? 1 m 329 2320 W U0 Un W U o\ I I E 225\v 255\ H MS 227 255 MS 20 20? [210 /21s 221 r218 1 250 fzasa I J W U0 Un W U M 205 *208 r211 I216 222 /219 1 3 231 234a x w Uo U! o\ w u o\, 1 HQ MS MS Patented March 1? Sheets-Sheet 2 48 66 A J FIG. ID

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D IL 0 H s E R H T B U s (VOLTS) NORMAL I DECAY SLOW DECAY SLOW NORMAL ATTACK ATTACK FIG. 3c;

Patented March 1972 v L 3,547,928

- v 17 Sheets-Sheet 9 4 Patented M r h 1972 3,647,928

17 Sheets-Sheet 10 .FIG. 8

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Patented March 7,1972 3,647,928

17 sheets-shut 12 Fig. [5A i 5 H as , O hmic SIGMOID es/\ .v i SWITCHING INTERVAL Threshold I I es 408 PHASE-SHIFT FILTERS VOICE I A STOPS T0 GATES OF VDC Patented March 7, 1972 3,647,928

17 Sheets-Shoot l 7 ELECTRICAL MUSICAL INSTRUMENT WITH ENSEMBLE AND CHIEF EFFECTS AND UNEQUAL STEREOPHONIC OUTPUTS RELATED APPLICATION This application is a continuation-in-part application of copending application Ser. No. 713,549 filed Mar. 18, 1968, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to the simulation of various kinds of pipe organs.

One major kind of pipe organ simulated by the invention is called a straight organ which has separate sets of pipes for each controlling stop, and richer ensemble and tonal effects than have other pipe organs which attempt to use given sets of pipes with more than one stop, in unification, octave coupling, and duplexing. Such attempts to limit the costs of pipe organs result in corresponding limitations in musical interest. Almost all prior art electronic organs attempt the same economies of independent tone sources and encounter equivalent or greater losses in musical interest. The present invention provides for the full efiects of a straight organ without costly proliferation of independent tone sources.

A further, broad class of pipe organs concerns classic organs. Classic organs are characterized by a predominance of diapason and flute stops or voices lacking prominent higher harmonics, by frequent use of compound stops in which a single stop and keyboard key actuate two or more pipes, by simultaneity of speech of different pipes sounded by a given keyboard key, by definite but pleasing and not excessive initial transient pipe sounds known as chiff, by tracker action or purely mechanical keying of pipe air valves enabling the player to control the rates of attack and decay, and hence the expression, of individual notes by the speed of key depression and release, by projection of pipe sound from organ cases only partially surrounding the pipes, by an absence of vibrato and tremolo, by an absence of loudness control by pipe-enclosing swell boxes with movable vanes, and usually by straight organ specifications. No prior art electric organ can simulate all of the above aspects of a classic organ, whereas the present invention can simulate all of them.

A still further broad class of pipe organs concerns romantic organs. Romantic organs are characterized by substantial complements, of string, woodwind, and reed and other voices having prominent higher harmonics, by limited use of compound stops, by nonsimultaneous speech of different pipes soundedby given keys, by an absence of chiff and the melodic and harmonic clarity it affords, by a loss of expression in individual notes because of electrically actuated pipe valves, by

more complete enclosure of most pipes, by common use of vibrato and tremolo, by swell control even of organ divisions other than the swell division, and by common unification, octave coupling, and duplexing, and corresponding departure from straight organ specifications.

A third class of pipe organs can still be found in the American movie organ, which sometimes grossly exaggerates the features of romantic organs and commonly adds such orchestral or band stops as drums, chimes, banjos, and so on.

Individual organs within any of the above classes characteristically vary from each other in marked degree, especially with respect to the number and kind of stops or voices. There are, also, many organs which partake of features of two or more of the above and other classes, so as to defy simple classification. Except perhaps for such sound effects as of drums and" the like, the present invention can simulate any pipe organ within, overlapping, or transcending the above classes.

This invention relates particularly to an electrical musical instrument having a pleasant ensemble quality.

The ensemble effect of independent tone sources in unison results basically from the fact that the sources are slightly out of tune with each other and variously distributed in space. Such an effect involves heard changes in loudness, pitch, location, movement, quality and identify of individual tones or of the collective tonal image. In contrast, synchronous sound waves from various sources produce a single louder tone which is like the component tones when they are alike in quality and intermediate between them when they difier.

Given instances of ensemble effects in pipe organs are found to vary with a number of different properties of individual pipes and their interrelations. Thus, the effects vary with the numerical difference in the frequencies of the sound waves from two or more pipes, with the amplitude of the weaker sound waves of a group, with the spatial arrangement of the pipes relative to each other and to listeners, with their number, and with the general type of speaking group they comprise (e.g., compound stops, stop combinations, replications of ranks, choruses, mixtures, comets, and celestes).

The spatial distribution of pipes, and their orientation to the listener, are especially important determinants of their ensemble effects. Thus, two pipes producing pure tones similar in pitch and placed close together in two adjacent ranks of a Celeste stop change rhythmically in loudness, apparent nearness, and pitch. This is the familiar beat, or monaural beat, which is created by mutual, alternate reenforcement and cancellation of the sound waves from the two pipes. Such beats are also heard when two pipes are at somewhat different distances but in line with the listener.

When, instead, two pipes are separated laterally relative to the listener, their resultant tones will not only vary in loudness, neamess, and pitch, but will also be heard as moving rhythmically back and forth between the pipe on the right and the one on the left. This stereophonic movement is called a binaural beat. When two slightly mistuned notes are conducted independently to the two ears, such lateral movement is almost their sole chorus effect, even though pitch changes like these as with physically moved tone sources can distinctly be heard. The lateral movement arises from the facts that one of the two slightly asynchronous sound waves leads the other in phase but in different degrees at the two ears, that this difference in priority and magnitude of the phase relationship gradually shifts back and forth between the two ears because the waves are asynchronous, and that the sound is heard as coming from the direction of the ear which hears the wave that happens to be leading more at a given moment. When the priority and degree of the phase leadership vary, but at all times are the same at the two ears, the major effect is the monaural beat noted above. In the binaural beat, the stereophonic movement is often not noticed for what it is, yet is definitely missed when it is absent. It is an essential aspect of authentic ensemble effects.

Slightly asynchronous sources of similar sound waves create the ensemble effect of a number of similar tones. Such tones are usually not distinguishable as separate tones, but the characteristic changes in loudness, pitch, location and movement clearly distinguish them as an ensemble from an equally loud, amplified, single tone. When such slightly mistuned tones differ also in quality it is correspondingly easier to distinguish them as separate tones. This invention achieves all such effects by differential stereophonic modulation of synchronous or asynchronous sources of sound.

The musical value of choruses, bands, orchestras or pipe organs depends substantially on the ensemble quality of the total sound from their many independent sources of tone (e.g., voices, solo instruments, pipes). Essentially for this reason, most electric organs include as many independent tone generators as practicable, together with devices or circuits for enhancing the ensemble effects of such generators. But ranks of independent generators are costly to manufacture, and most of the devices for enhancing their ensemble effects are either ineffective or bulky and expensive.

One type of prior art electric organ produces different pitches by means of a single, full rank of electromagnetic tone generators which, in effect, are all rigidly coupled together mechanically, so that there is not possibility of random, mutual mistuning and its correspondingly enhanced ensemble effects. Higher octave frequencies remain exact integral multiples of lower octave frequencies, so as to preclude a major source of such effects. All the generated waves are approximately sinusoidal or are made so by filters, and all the other, nonsinusoidal waveforms are produced by controllable mixtures of the generated or filtered, sinusoidal waves. The resulting lack of interactions between pronounced overtones on the one hand, and higher fundamental frequencies which are slightly asynchronous with these overtones on the other, limits profoundly the capacity of the instruments to produce ensemble effects.

Certain accessory devices can compensate partly for some of these limitations. Thus, devices or circuits which more or less rhythmically shift the phases of the produced audio frequency currents themselves can produce an authentic vibrato (which is fundamentally a slight rhythmic change in pitch at about 5 to 8 Hz., as distinguished from tremolo, or a comparable but usually less pleasant pulsation in loudness). By replication of such phase-shifting circuits, even individual vibratos for separate voices or groups of voices can be achieved. However, the greater effect of the phase-shifting circuits on the higher pitches in sometimes unpleasant and exaggerated, and such modulation of the lower frequencies produces beats similar ineffect to unsynchronized piston engines in airplanes.

Some circuits which shift the phases of audio frequency currents at subsonic rates much slower than vibrato do not produce satisfactory celeste (complexly and slowly beating and moving, organ string tones) or ensemble effects, because they produce relatively persistent changes in pitch which sound like a phonograph with excessive wow. Also, none of the circuits produces the spatial qualities of authentic ensemble effects,

Rhythmically mbved loudspeakers or similarly moved reflecting surfaces in the vicinity of stationary speakers can produce not only authentic vibrato, but, when moved more slowly, certain aspects of celeste or ensemble effects. The slight rhythmic departures from given pitches, effected by such equipment comprise changing Doppler effects which diminish 0r disappear during the relatively quiescent phases of the slower rhythms so as to preclude the relatively sustained mistuning and corresponding wow produced by some very low frequency phase-shifting circuits proper. Another system involves two speakers, at least one of which is dynamic. The direct currents which actuate the field coil of the dynamic speaker which radiates bass tones, are alternately and oppositely modulated at subsonic frequencies so as to achieve effects somewhat like those produced by moving speakers or reflectors, through effecting stereophonic movement of radiated tones equivalent to that produced when only a single stereophonic modulation takes place.

Still another system modulates tone frequency currents in two essentially asynchronous, random, subsonic patterns, and projects the two differently modulated versions of the tone frequencies stereophonically, to produce paradoxical ensemble effects of a single tone. A variant of this system modulates each of a plurality of differently shaped, synchronous tone frequencies in a single, distinctive, random, subsonic pattern, and radiates each of these tone frequencies monophonically from its own separate amplifier-speaker system, to produce overall stereophonic effects among the plurality of speakers.

However, in all instruments other than the present one, successful achievement of simultaneous or multiple, vibrato, celeste and ensemble effects among different tones or voices based on synchronous currents cannot be achieved without manifold replication of the bulky and costly speaker systems.

Most contemporary makes of electric organ involve a single set of 12 mutually independent tone generators, or one generator for each note of a single octave of the chromatic scale, together with frequency multipliers or dividers which supply frequencies for the remaining octaves so that higher octaves are exact integral multiples of lower ones. The slight departures from the chromatic scale which arise from inevitable, slight mistuning of the 12 generators add to the normal beat effects of the chromatic scale, and offer closer approximations to ensemble effects than are possible with fully interlocked generators. However, the fixed, integral relationships of higher to lower octave frequencies, as these frequencies are established by the frequency multipliers or dividers, severely limit the capacity of these instruments to achieve the ensemble effects which different and frequently exploited coupler stops normally enable a pipe organ to produce. Also, such 12- generator electric organs may involve many different wave shaping and mixing circuits but they typically make no provision for ensemble effects between the resulting tone qualities. Thus for most of these instruments, the wave shapers produce only overall tonal mixtures and not ensemble effects as well.

Several contemporary makes of electric organ have at least one full rank of independent tone generators which provide a different, independent, original frequency for each pitch of an entire organ scale. Octaves and other intervals sounded on such instruments manifest greater ensemble effects, espe.ially in connection with voices whose prominent overtones interact with the slightly mistuned fundamental tones and overtones of higher pitches. Actually, most models of these organs embody two or more full ranks of the generators, with corresponding enhancement of ensemble effects as well as greater tonal variety. However, the additional ranks involve corresponding and substantial increases in cost, and spatial distributions of individual tones are lacking; except for a few electric organs which play different voice groups through two or more different amplifier-speaker systems, all notes from such instruments emerge from the same speaker or speakers; no prior art electric organ succeeds in reproducing or closely approximating the authentic, spatial, sound effects of differently located, individual organ pipes.

This invention also relates particularly to an electrical musical instrument simulating the sound effects of air in organ pipes.

Prior art electric organs have generally been incapable of achieving the subtle sound effects of natural air turbulence in organ pipes. Furthermore, prior art organs have been incapable of achieving slight and pleasant changes in pitch and ensemble effects which occur when many pipes of a pipe organ speakfThis sound effect is to be distinguished from the unpleasant changes in pitch and exaggerated ensemble effects characteristic of a pipe organ with grossly inadequate wind pressure.

This invention still further relates particularly to electric organs capable of producing and modulating exact harmonic pitch registers similar to those of pipe organs.

It is necessary to produce and modulate exact harmonic pitch registers to accurately simulate the mutation and compound stops of a pipe organ. The common practice of electronic organ manufactures which relies upon the nearest tempered scale note in place of exact harmonics in mutation and compound stops has failed to simulate the mutation and compound stops of a pipe organ. In general, such a practice has markedly reduced the ensemble effect and musical interest of the common electronic organ.

This invention also relates particularly to electric organs exhibiting chiff.

Chiff is a transient tone of higher frequency then the fundamental tone, which appears briefly before or during the onset of the fundamental tone when the key is depressed, and sometimes as terminal transients when the key is released. Chiff frequencies may be either harmonics or inharrnonics of the fundamental, and lend assertiveness and clearer identity to the sounded tones. Most prior art electric organs do not exhibit chiff.

SUMMARY OF THE INVENTION One object of the present invention is to achieve indefinite extension of authentic ensemble effects with less bulky and expensive equipment, for any desired numbers of keyboards,

Claims (21)

1. An electrical musical instrument having an ensemble quality comprising: a plurality of tone frequency current sources, a first plurality of modulators having at least first and second outputs and first and second inputs, the outputs of selected ones of said tone frequency current sources being applied to said inputs, said modulators causing the level of at least one tone frequency current appearing at said outputs to vary in subsonic, different, alterations between said first and second outputs, and a stereophonic amplifier-speaker system including first and second speakers, the first output of said modulator units being applied to said first speaker and the second output being applied to said second speaker so that the levels of the two tones as reproduced by said speakers vary in different relative subsonic patterns in each of said speakers.

2. The electrical musical instrument recited in claim 1 having: at least 12 independent continuously operating tone frequency current sources, frequency-multiplying means, the outputs of said tone frequency current sources being applied to said frequency multiplying means to produce frequency currents corresponding to the tones in the chromatic scale of different octaves, and a second plurality of modulator units, each having at least two outputs and two inputs, said frequency current sources being applied to the inputs of said second plurality of modulator units, the outputs of said second plurality of modulator units being applied to the inputs of said first plurality of modulator units, said second plurality of modulator units causing the level of at least one tone frequency current appearing at the outputs thereof to vary in subsonic alterations so that the frequency currents which originate from the same tone source are distinctive one from the other in the variation of subsonic alterations.

3. The electrical musical instrument recited in claim 1 wherein each modulator unit includes: a plurality of stop switches controlling the application of tone frequency current to said outputs of said modulator units, a voltage divider network, a source of voltage being applied through said stop switch to said voltage divider network so that a subthreshold voltage appears across the output of said voltage divider network when only one of said stop switches is closed and a threshold voltage appears across said output when more than one of said stop switches are closed, and a controlled switching device responsive to said threshold voltage to actuate all of the modulator units having closed stop switches to cause the amplitudes of the tone frequency current to vary in subsonic alterations at the outputs of said modulator units.

4. An electrical musical instrument having: a plurality of tone sources, a stereophonic amplifier-speaker system including first and second speakers, a plurality of keys for selectively applying tones from said sources to said amplifier-speaker system, register coupling means for applying tones of a desired register to said amplifier-speaker so that first and second tones added by the depression of two different keys may originate from the same tone source, the improvement comprising: first and second register modulator units each having at least one output and one in put, said modulator units causing the lEvel of the tone appearing at said output to vary in subsonic alterations, the subsonic alterations of said first and second register modulator units being asynchronous, and means for applying said first and second tones to the inputs of said first and second register modulator units, respectively, so that said first and second tones are heard as an ensemble of tones with added intensity.

5. An electrical musical instrument in which each tone has a different general location in space comprising: a plurality of wave shapers, each producing at least first and second outputs of unequal amplitude, the inequality in amplitude between said first and second outputs being different for different wave shapers, a plurality of continuously operating tone frequency current sources, each producing an output having a frequency related to a tone in the chromatic scale, the outputs of said tone frequency current sources being selectively applied to the inputs of said wave shapers, and a stereophonic amplifier-speaker system including first and second speakers, the first output of each wave shaper being applied to said first speaker and the second output of each wave shaper being applied to said second speaker, the inequality in amplitude between said first and second outputs giving each of the tones reproduced by said speakers a different general location in space.

6. An electrical musical instrument having an ensemble quality comprising: a plurality of tone frequency current sources, a plurality of modulator units each having at least first and second outputs, first and second inputs, and a source of mutually asynchronous subsonic frequency signals, the outputs of selected ones of said tone frequency current sources being applied to said inputs, said asynchronous subsonic frequency signals modulating the tone frequency currents to cause the level of the tone frequency currents appearing at said outputs to vary in subsonic, different, alterations between said first and second outputs, and a stereophonic amplifier-speaker system including first and second speakers, the first output of said modulator units being applied to said first speaker and the second output being applied to said second speaker so that the levels of the tones as reproduced by said speakers vary in different relative subsonic patterns in each of said speakers.

7. The electrical musical instrument of claim 6 wherein the asynchronous subsonic frequency signals produced by said source are random.

8. The electrical musical instrument of claim 6 wherein the asynchronous subsonic frequency signals produced by said source are rhythmic.

9. The electrical musical instrument of claim 6 wherein the asynchronous subsonic frequency signals produced by at least one source are random and the asynchronous subsonic frequency signals produced by at least one other source are rhythmic.

10. The electrical musical instrument of claim 6 wherein the asynchronous subsonic frequency signals produced by said source are in the range of 6 to 16 Hertz whereby the levels of the two tones as reproduced by said speakers vary in different relative subsonic patterns in each of said speakers so as to simulate the subtle sound effects of natural air turbulence.

11. The electrical musical instrument of claim 10 wherein said source produces a variable band of asynchronous subsonic frequency signals for modulating said tone frequency current sources whereby different and variable relative subsonic patterns are reproduced in each of said speakers dependent upon the band of said asynchronous subsonic frequency signals so as to simulate wind-pressure changes of a pipe organ.

12. An electrical musical instrument simulating the subtle sound effects of natural air turbulence in organ pipes comprising: at least one tone frequency current source, at least one modulator means having an input, first and second outputs, and a source of subsonic frequency signals for modulating the tone frequencY current from said tone frequency current source, said modulator means causing the level of said tone frequency current appearing at said first and second outputs to vary in subsonic, different, alterations between said first and second outputs, and a stereophonic amplifier-speaker system including first and second speakers, the first output of said modulator means being applied to said first speaker and the second output being applied to said second speaker so that the levels of the two tones as reproduced by said speakers vary in different relative subsonic patterns in each of said speakers thereby simulating the subtle sound effects of natural air turbulence in organ pipes.

13. The electrical musical instrument of claim 12, wherein said subsonic frequency signals lie in the range of 6 to 16 hertz.

14. An electrical musical instrument simulating the wind-pressure variations of a pipe organ comprising: at least one tone frequency current source, at least one modulator means having an input, first and second outputs, and a source of variable band subsonic frequency signals for modulating the tone frequency current from said tone frequency current source, said modulator means causing the level of said tone frequency current appearing at said first and second outputs to vary in subsonic, different, alterations between said first and second outputs, and a stereophonic amplifier-speaker system including first and second speakers, the first output of said modulator means being applied to said first speaker and the second output being applied to said second speaker so that the levels of the two tones as reproduced by said speakers vary in different and variable relative subsonic frequency patterns in each of said speakers and upon the frequency of said variable band the subsonic frequency signals in each of said speakers thereby simulating the wind-pressure variations of a pipe organ.

15. An electrical musical instrument comprising: a plurality of tone frequency current sources, a plurality of chiff frequency current sources, a plurality of modulator means, each of said modulator means coupled to one of said tone frequency current sources and one of said chiff frequency current sources, a plurality of switch means for applying said chiff frequency currents to said plurality of modulator means briefly before or during the onset or termination of the application of said tone frequency currents to said plurality of modulators so as to lend assertiveness and clearer identity to sounded tones, and an amplifier-speaker system coupled to the output of said modulators producing assertive tones having clear identities.

16. The electrical musical instrument of claim 15 wherein said plurality of switch means comprises sigmoid switches for applying the tone frequency currents and the chiff frequency currents to said modulator units in a manner eliminating transient noise by affecting gradual changes in amplitude during the beginning and ending of both attack and decay of switching currents and controlling the overall abruptness of the attack.

17. An electrical musical instrument for producing harmonic and nonharmonic tones simulating stops of a pipe organ: a plurality of keyed control means, a plurality of tone frequency current sources associated with said keyed control means, each of said tone frequency current sources associated with one of said keyed control means and generating tone frequency currents comprising a fundamental and at least one harmonic, a plurality of modulators associated with each fundamental and harmonic output of said tone frequency current sources for modulating the fundamental and harmonic tone frequency currents so as to produce a pair of tone frequency current outputs varying in subsonic, different, alterations between the outputs of each of said modulators, a stereophonic amplifier-speaker system including first and second speakers, both of said tone frequency current outPuts of each of said modulators being applied to said first and second speakers respectively, keyed switching means associated with each of said modulators for applying fundamental and harmonic tone frequency currents to said modulators in response to said keyed control means, each of said keyed control means operating a different group of keyed switching means corresponding to a stop associated with a group of modulators which are in turn associated with a group of tone frequency current sources, and a plurality of stop switching means for applying the pair of tone frequency current outputs from each of said group of modulators to said pair of speakers to produce two tones at said first and second speakers which vary in different relative subsonic patterns at each of said speakers.

18. The electrical musical instrument of claim 17 wherein each of said plurality of said tone frequency sources comprises a single signal source and a plurality of filters for deriving signals corresponding to a fundamental tone and at least one harmonic tone.

19. The electrical musical instrument of claim 18 wherein said keyed switching means comprise sigmoid switches.

20. The electrical musical instrument of claim 19 comprising means for generating modulating signals applied to each modulator of any one group of said modulators, each of said modulating signals applied to one of said modulators in the group having a different subsonic frequency pattern from every other modulating signal applied to the other modulators in the group.

21. The electrical musical instrument of claim 20 wherein said means for generating modulating signals comprises a plurality of subsonic frequency signal sources, each of said modulating signals applied to one of said modulators in the group comprising signals combined from a different combination of said subsonic frequency sources.

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