MOTM

You can't really use audio, even amplified, as an effective controller
directly (unless you want some really weird sounds of course). The
individual rises-&-falls of an audio waveform aren't typically what you want
to derive as a control 'signal.' What you want is the 'envelope,' the
overall, *average* changes in amplitude of a signal, not the individual wave
cycles. An Envelope Generator creates these from scratch; an Envelope
Follower [ / Trigger Detector], such as the forthcoming MOTM module as I
understand it, allows you to extract this average amplitude information from
an existing sound source and use it anywhere you want to in your modular
patches.

Typically, an EF is created by taking the amplified input signal, running it
through a full-wave rectifier (so that the portions of the waveform that go
negative are 'flipped-up' and are sitting in between their positive
counterparts) and then filtering out the ripple. This filter is often
adjustable so that you can cater it to your sound---it is often labeled as a
'response' switch (fast/med/slow). You then have a DC output voltage that
basically 'follows' the rises and falls, overall, of your input signal. Some
EF's have an overdrive stage at the input because square-ish waveforms will
rectify more nicely into something more like DC and require less filtering,
and therefore you can keep a snappy response using lighter filtering.

Typical uses for an envelope follower include an auto-wah effect, where the
EF CV out is fed to a Lowpass filter that is processing the original
acoustic signal.

Another feature of a typical EF is the "Trigger/Gate Detector" portion,
nothing more than a comparator that watches the EF's CV output and goes high
when a threshold is exceeded. This can be used in the auto-wah example to
feed an EG that controls the LP cutoff frequency, so that rather than the
wah being controlled by the loudness of the original signal, you can impose
an artificial envelope onto it.

 -----Original Message-----
From: 	mark scetta [mailto:n0nspaz@...] 
Sent:	Thursday, 09 March, 2000 11:43 AM
To:	motm@onelist.com
Subject:	Re: [motm] Digest Number 395

From: mark scetta <n0nspaz@...>

ah. so i will try to trigger my arp omni ii's gate along with my original 
audio source at the same time in order to get the envelope i need. but, if 
my audio has a fast attack, and i preamp'd it, wouldn't that create a large 
enough voltage to open the gate on the EG? ah, but then i'd have to close 
it.....i think i am getting this. thanks guys.