Sound Synthesizer Creates New Musical Effects

Gh..ot L'', 0 va,J -ci, Lr1"t .t a, col-'~-~ electronics December 1, 1961

Author sets up tonal effects on synthesizer. Conventional tape deck at top, tape-loop reverberation below, and plug-in modules at bottom

Well-known electronic circuits are used in system combinations so that, unconventional sounds and patterns can be produced from ordinary audio. For example, a singer can generate his own string bass accompaniment simultaneously with his voice

BV HARALD BODE The Wurlitzer Company, North Tonawanda, New York

NEW SOUNDS 100 and musical effects can 350 be created either by synthesizing 700 1050 acoustical phenomena, by processing natural or artificial (usually electronically 50 100 200 300 500 1,000 1,500 CPS generated) sounds, INPUT 1 or by applying both methods. Pro- (B) INPUT 2 INPUT I cessing acoustical phenomena often results in substantial deviations 250 450 from the original.

100 800 Production of new sounds or mu- 950 sical effects can be made either by 1150 intermediate or immediate process- 50 100 200 300 500 1,000 1,500 CPS ing methods. Some methods of in- (C) 0U PUT T termediate processing may include punched tapes for control of the FIG. 1-Ring-bridge modulator (A) with input signals, (B) cord output (C) parameters of a sound synthesizer, and may also include such tape re- 10,000 cording procedures as reversal, pitch-through-speed 5,000 changes, edit- ing and dubbing. 2,000 Because of the time differential between production and perform- 1'000 880 ance when using the intermediate 500 440 process, the composer-performer Z zoo cannot immediately hear or judge his performance, therefore correc- 100 tions can be made only after some 50 lapse of time. Immediate processing techniques presents no such 20 problems. 10 Methods of immediate processing CPS include spectrum and envelope shaping, change of pitch, change of overtone structure including modi- fication from harmonic to non- harmonic overtone relations, application of periodic modulation effects, reverberation, echo aind FIG. 2-Output of ring-bridge modulator with gliding frequency applied other repetition phenomena. to one input and two harmonically related frequencies to the other The output of the ring-bridge

NEW FRONTIERS IN ELECTRONIC MUSIC ment making marked the growth of Music is the art of making pleas- tionships. purely instrumental music. The ing, expressive or intelligible com- Early church music gave us the modern symphony originated in the binations of sounds and making neumes to indicate pitch, the de- time of Haydn and others about such combinations into composi- velopment of staff notation, and 1770. tions of definite structure and sig- the superseding of the tetrachord Recently, increasingly dissonant nificance according to the laws of unit by the hexachord. The practice linear counterpoint, Schoenberg as melody harmony and rhythm. It is of descant, or simultaneous melody, an example, is becoming popular. also the art of inventing, writing gave rise to mensurable music The French gave us polytonality or rendering such compositions, which in turn gave birth to counter- and the Russian composers have whether vocal or instrumental. point. given us barbaric, dynamic rhythms Ancient Greek music was limited Establishment of modern major while American jazz has contrib- in expression by the primitive in- and minor scales with the octave uted to the music of the dynamic struments used, mostly of the lyre as a unit and of equal temperament era in which we live. and flute types. However, it did made possible modulation into any Modern proponents of musical establish the diatonic scales based key and led to the development of thought and expression have often on the tetrachord as a unit and harmony. complained of being musically re- gave us the rudiments of key rela- Great improvements in instru- stricted by instrument range and, Front panel of tape-loop reverberation and modular units (left) with top view of module chassis (right) modulator shown in Fig. 1A yields quencies are no longer harmonically congruent envelope shaping as well the sum and differences of the fre- related to each other. If a group as the coincident percussive en- quencies applied to its two inputs of properly related frequencies were velope shaping of the program ma- but contains neither input fre- applied to both inputs and a percus- terial. One input accepts the con- quency. This feature has been used sive-type envelope were applied to trol signal while the other input ac- to create new sounds and effects. the output signal, a bell-like tone cepts the material to be subjected Figure 1B shows a tone applied to would be produced. to envelope shaping. The processed input 1 and a group of harmonically In a more general presentation, audio appears at the output of the related frequencies applied to input the curves of Fig. 2 show the vari- gating circuit. 2. The output spectrum is shown ety of tone spectra that may be de- To derive control voltages for the in Fig. 1C. rived_,with a gliding frequency be- gating functions, the audio at the Due to operation of the ring- tween 1 cps and 10 Kc applied to control input is amplified, rectified bridge modulator, the output fre- one and two fixed 440 and 880 cps and applied to a low-pass filter. frequencies (in octave relationship) Thus, a relatively ripple-free vari- applied to the other input of the able d-c bias will actuate the vari- ring-bridge modulator. The output able-gain, push-pull amplifier gate. frequencies are identified on the, When switch St is in the gating po- graph. sition, the envelope of the control Frequencies applied to the ring- signal shapes that of the program bridge modulator inputs are not material. compost-~ color ; thus most of their limited to the audio range. Appli- To prevent the delay caused by tions cannot express the emotions control they feel and wish to communicate. cation of a subsonic frequency to Ct and C. on fast-changing New forms of music await, new type one input will periodically modulate voltages, and to eliminate asym- instruments or the development of ;a frequency applied to the other. metry caused by the different out- sound synthesizers that can pro- Application of white noise to one put impedances at the plate and duce all possible audio tones, in input and a single audio frequency cathode of V relatively high-value any combination, at any amplitude, to the other input will yield tuned resistors R:, and R, are inserted be- and with any form of envelope noise at the output. Application of tween phase inverter V, and the shaping that will enable any imag- a percussive envelope to one input push-pull output of the gate circuit. inable combination of tones to be simultaneously with a steady tone These resistors are of the same or- played. at the other input will result in a der of magnitude as biasing re- Synthetically produced sound R, secure bal- offers a broad canvas upon which percussive-type output that will sistors and R_ to a all tones, regardless of their nature, have the characteristics of the ance between the control d-c signal can be painted, thus opening new steady tone modulated by the per- and the audio portion of the pro- avenues for the composers of to- cussive envelope. gram material. morrow The unit shown in Fig. 3 provides The input circuits of V. and V, PIG. .3-Audio-controlled gate and percussion unit

act as a high-pass filter. The cut- To make the trigger circuit re- triggers the percussion circuit, off frequency of these filters exceeds spond to the beginning of a signal which in turn converts the sus- that of the ripple filter by such an as well as to signal growth, differ- tained chords played by the organ amount that no disturbing audio entiator C., and Re plus R, is used into percussive tones. The output frequency from the control input at the input of Ve. The response to signal is applied to a tape-loop repe- will feed through to the gate. This signal growth is especially useful tition unit that has four equally is important for clean operation of in causing the system to yield to a spaced heads, one for record and the percussive envelope circuit. The crescendo in a music passage or to three for playback. By connecting pulses that initiate the percussive instants of accentuation in the flow the record head and playback head envelopes are generated by Schmitt of speech frequencies. 2 in parallel, output A is produced. trigger V, and V,o. Positive-going The practical application of the By connecting playback head 1 and output pulses charge C., (or C.; plus audio-controlled . percussion device playback head 3 in parallel, output Ca or C, chosen by S,) with the dis- within a system for the production B is produced, and a distinctive charge through R5. The time con- of new musical effects is shown in ABAB pattern may be achieved. stant depends on the position of S,. Fig. 4. The sound of a bongo drum Outputs A and B can be connected

FIG. 4-Organ chords are given drum envelope to produce musical drum effect. Other instruments, including voice, way be substituted for the organ

to formant filters having different ring-bridge modulator is applied lables-would trigger the circuit. resonance frequencies. through filter 2 to the mixer. At At the output of the audio-con The number of repetitions may the mixer output a percussive trolled gate, percussive sounds with be extended if a feedback loop is ARAB signal (stemming from a the voicing of a string bass will be inserted between playback head 2 single melody note, triggered by a obtained mixed with the original and the record amplifier. The out- single drum signal) is obtained. In voice of the singer. The human put voltages of the two filters and its A portion it has the original voice output signal will now be ac- the microphone preamplifier are ap- melody instrument pitch while its companied by a coincident string plied to a mixer in which the ratio B portion is the converted nonhar- bass sound which may be further of drum sound to modified percus- monic overtone structure, both af- processed in the tape-loop repeti- sive organ sound may be controlled. fected by the different voicings of tion unit. A presentation dealing more spe- the two filters. When the direct The arbitrarily selected elec- cifically with the tape-loop device drum signal is applied to a third tronic modules of this synthesizer and the sound-processing modules mixer input, the output will sound are of a limited variety and could used in the synthesizer is shown in like a voiced drum with an intricate be supplemented by other modules. Fig. 5. aftersound. The repetition of the A system synthesizer may find The program material originat- ABAB pattern may be extended by many applications such as explora- ing from the melody instrument is a feedback loop between playback tion of new types of electronic mu- applied to one of the inputs of the head 2 and the record amplifier. sic or as a tool for composers who audio-controlled gate and percus- When applying the human sing- are searching for novel sounds and sion unit. There it is gated by the ing voice to the input of the funda- musical effects. Such a device will audio from a percussion instrumental frequency selector, the ex- present a challenge to the imagina- ment. The percussive melody tracted fundamental pitch may be tion of composer-programmer. sounds at the output of the gate are distorted in the squaring circuit The modern approach of synthe- applied to the tape-loop repetition and applied to the frequency divider sizing intricate electronic systems system. Output signal A-the di- (or dividers) . This will derive a from modules with a limited num- rect signal and the information melody line whose pitch will be one ber of basic functions has proven from playback head 2-is applied octave lower than that of the successful in the computer field. through amplifier A and filter 1 to singer. The output of the frequency This approach has now been made the mixer. Output signal B-the divider may then be applied through in the area of sound synthesis. signals from playback heads 1 and a voicing filter to the program input With means for compiling any 3-is applied through amplifier B of the audio-controlled gate and desired modular configuration, an to one input of the ring-bridge percussion unit. The control input audio system synthesizer could be- modulator. The other ring-bridge of this circuit may be actuated by come a flexible and versatile tool for modulator input is connected to the the original singing voice, after sound processing and would be output of an audio signal generator. having passed through a low-pass suited to meet the evergrowing de- The mixed and frequency con- filter of such a cutoff frequency mand for exploration and produc- verted signal at the output of the that only vowels-typical for syl- tion of new sounds.

TAPE LOOP

WRITE READ I -i READ 2 READ 3

PERC INSTR

MELODY INSTR

DISTRIBUTER FIG. 5-Overall synthesizer system with tape-loop device and sound and envelope shaping units. Various combinations of shaping circuits can be patched together to generate desired tonal effects