better envelopes

[felixroos]

envelopes will have pops when the hap is shorter than attack + decay. cancelAndHoldAtTime supposedly fixes this (in chrome only, see https://bugzilla.mozilla.org/show_bug.cgi?id=1308431 which is blocked by WebAudio/web-audio-api#2437). it seems there is actually no real solution right now??
some clues could be found in one of:

• https://andremichelle.github.io/web-audio-api-automator/ (adsr timeConstant)
• https://github.com/velipso/adsrnode
• https://github.com/Tonejs/Tone.js/blob/aa58bf7fd1c045a35b819aa2e1f9e1bdf39dd204/Tone/component/envelope/Envelope.ts

[felixroos]

another design that could be chosen is to just add a t = Math.max(t, begin + attack + decay) inside stop returned by getEnvelope to make sure the sound duration is at least completing the attack and decay phase (reaching sustain level) before starting the release. This should prevent all pops + might even be musically useful

[felixroos]

fixed with #861