[sdiy] Question about Envelopes

[Gordonjcp]

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