[sdiy] Question about Envelopes

[Ben Bradley]

>Yes, I think 'envelope' in synth jargon comes from the envelope in the term 'modulation envelope' from AM radio engineering.

Yes, I think this is the origin (not that it does a whole lot to
explain synth envelopes). A phrase I've heard in amateur radio is
"peak envelope power" for a modulated signal (whether AM or Single
Sidebamd), the peak power of the RF.

But the thing is an ADSR/EG does NOT generate an envelope by itself,
it only generates a control voltage! Its CV output controlling a VCA
with an audio signal through it generates an envelope.

The way I'd describe its use is in regards to attack, sustain and
decay of different instruments. Guitar and piano notes get to full
volume instantly, then slowly fade away.  Violin, horn and pipe organ
tones have a slower attack and build up over a fraction of a second,
then sustain as long as the player can keep it going. The ADSR
controlling a VCA lets you emulate/simulate these things, at least the
volume portion of the sound.

The timbre also changes with time, and that can be simulated with
another 'envelope' generator controlling a voltage controlled filter,
but for that one I suppose it might be called something different than
an envelope. I've seen the word contour used, but perhaps it could be
called a "dynamic timbre generator."

Also, I promise never to complain about 'reply-all' again, regardless
of how many times I make the mistake...


On Thu, Nov 30, 2017 at 4:21 AM, Gordonjcp <gordonjcp at gjcp.net> wrote:
> On Wed, Nov 29, 2017 at 09:41:51PM -0800, Stephan Vladimir Bugaj wrote:
>> It comes from mathematical physics and the concept of the enveloping
>> curves that tangent the inflection points / outline the extremes of
>> the signal.
>
> This, exactly.  The word "envelope" in this context describes the area
> enclosed by a curve.  Think in terms of "performance envelope" used in
> (for example) aircraft dynamics, where you'd draw a patch on a graph of
> speed versus altitude that describes the maximum and minimum airspeed
> possible at different air pressures.
>
> It comes from the French word "enveloppe", which was a verb meaning to
> wrap or cover something, from which we get the noun form meaning a thing
> you wrap or cover something with.
>
> --
> Gordonjcp
>
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