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The Sensuous Envelope Follower | |
Article from Polyphony, November 1977 |
Now that I've got your attention with that title, let me ask you, what do you use your envelope follower for (providing you use it at all)? I'll bet quarters to quadrature oscillators you've answered, "To convert external sound sources into control voltages for use by voltage controlled elements" and you would be right. Fact is, most folks use their envelope followers for precisely that; you plug a guitar, microphone, or what have you, into the thing and out comes a proportionate voltage with the same amplitude envelope as the input (plus a trigger and gate on better models). Usually this voltage is used to control the element through which your external signal is simultaneously being processed. This is fine — after all, an envelope follower is primarily designed to be used in such fashion, but remember that the single-minded use of any music module is un-creative and contrary to the spirit of music!
One of the beauties of the synthesizer is that it is, as Dr. Moog would say, "Not an instrument, but a collection of instruments" which may be exploited in a variety of ways. The envelope follower — one of those instruments — should be no exception. For instance, would you use your LFO solely for producing vibrato in a voltage controlled oscillator? Of course not! You most probably have used it to modulate your VCA, PWM, filters, you name it — yet I have known people who wouldn't hesitate to use their LFO's in the most bizarre applications, but would not even conceive of using their envelope followers for more than generating a control envelope from an external source!
Keeping all of this in mind, let us now re-examine the underplayed envelope follower (E.F.), in the light of creativity and consider some new applications.
I. Pitch Follower.
Your 2720-11 can act as a pitch follower by exploiting the fact that amplitude, which your E.F. detects, often varies proportionately with pitch. Normally this change is far too small for the human ear to discern.
Providing that the input signal is not of great harmonic complexity, proceeds smoothly from note to not and is not so low in frequency as to cause a ripple on the output voltage, very satisfactory results can often be obtained.
A "horn blip" is a short duration transient which proceeds the normal amplitude envelope on notes produced by brass instruments (figure 2a). This phenomenon gives them their characteristic "bite". The synthesis of brass instruments usually requires an ADSR to generate the primary envelope and an AR to create the horn blip — the outputs of both instruments being summed in the VCA — but by once again calling upon the multifarious envelope follower, it is possible to create a "brass" envelope, complete with horn blip, with the AR alone.
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Feature by John A. Mitchell
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