ADSR produces small step and audible click in decay or release phase

[sdiedrichsen]

https://es-daisy.slack.com/archives/CU7QB1K5Y/p1620032978070300

There's a rather unfortunate comparison, which forces the output to zero once the envelope falls below 0.01.

I'd suggest using a negative target value for the the filter and clip the output at zero. Also, for the attack a target value > 1.0 produces a more pleasant attack phase.

[jasonmayo]

There are situations where it would be useful to set ADSR_SEG_IDLE at a given level, such as prioritising voices for polyphonic voice assignment. Could the current 0.01 be a default that can be overridden?
if(out <= idle_threshold)

[sdiedrichsen]

I'd tend to disagree a bit, the ADSR should produce a clean envelope primarily. But for voice allocation or stealing a accessor method for the segment might be useful.

[sdiedrichsen]

OK, here's my remake:
#160

[sdiedrichsen]

This has been merged, so this issue can be closed now.