Apply envelope & panning after biquad filtering.
This may fix the weird popping problem. It also reduces the number
of operations that are done "in stereo", so it could help performance.
It also fixes a previously unnoticed problem where a ring-modulated
waveform had 2x the amplitude of an un-modulated waveform.
The test differences look large but it's because some values got changed
in the LSB after the mathematical divisions were moved around.
Semi-incompatible name change: The method `release_then_press`
is now `change`. For now a compatibility alias is supported.
Everywhere a `NoteSequence` was accepted, a single note is now accepted.
So for instance, `synth.press(30)` can be written instead of requiring
``synth.press((30,))`. The same goes for `change.retrigger`, which
will accept a single LFO or a sequence.
When there's no sustain, the release step needs to be calculated from
the attack level, not the sustain level. Otherwise, contrary to intent,
this leads to the actual release taking a loooonnngg time.
A note can be placed in the center (panning=0) or moved to just the left
(panning=1) or right (panning=-1) channels. Fractional panning values
place it partially in both channels.
Now the vibrato 'units' are 1.0 = one octave, 1/12 = one semitone,
1/1200 = one cent. Before, the units were somewhat arbitrary and were not
perceptually "symmetrical" around the base frequency.
For vibrato_depth = 1/12 and base frequency of 440,
before: pitch from 403.33 to 476.67Hz, not corresponding to any notes
after: pitch from 415.30 to 466.16Hz, corresponding to G# and A#
this has the side effect of making some notes more accurate, the new
frequency= value in the test is closer to the true midi frequency of
830.609...Hz.
and re-vamp overall envelope calculation again.
Now, if you set a low overall attack level like 0.2 this avoids the
"diminishing volume" effect when many notes sound at once. You need
simply choose a maximum attack level that is appropriate for the max
number of voices that will actually be played.
.. and account releasing notes at their sustain level until they're
done.
this ameliorates the effect where multiple releasing notes
don't seem to actually be releasing, but stay at a constant volume.
This class allows much more expressive sound synthesis:
* tremolo & vibrato
* arbitrary frequency
* different evelope & waveform per note
* all properties dynamically settable from Python code
