Complex Envelopes.

Some experiments with ideas for creating complex envelopes.

1. Uses the Multi-stage EG to create a four stage attack + sustain, then
uses a logic inverter & pulse to trigger a four stage release envelope when
the key is released.

2. Uses a control sequencer for a looping pattern until the key is released,
then the gate controls a crossfader to switch to a long release envelope.

3. Uses a standard ADSR for the A & R  portions, but when it reaches the
sustain level, a compare module switches a crossfader to a pattern
generator. Each new note gets a different pattern. Interesting effects when
you hold chords. Then when the key releases, & the sustain level drops, the
crossfaders switches back to the ADSR for the release.

4. Similar to #3, this one combines a sequencer & AR EG for the sustain
loop, and processes them through a note quantizer for a descending melodic
pattern during the sustain.
