[bdbarnett]

Hold a chord and turn Cutoff: you now hear the sweep. Until now every instrument read its macros when a note started, so set_macro() reached only the next note, and a filter sweep over a held note, the most basic synth gesture, wasn't possible.

Fixes #166.

What you'll hear

On all 43 melodic instruments, the continuous macros reach the notes that are already sounding, on their next audio block: volume, filter cutoffs and resonance, layer mixes, filter-envelope amounts, brightness and tone controls, drive, and modulation depths and rates. That is 246 macros in all.

A macro set before a note sounds exactly as it did before this change. Every instrument, every macro at 0, 64 and 127, renders byte-identical to the previous release on CPython, MicroPython and CircuitPython.

What still waits for the next note, and why

• Envelope times and levels, glide, voice and unison modes, patches. These describe how a note is struck, so they belong to the next one.
• Pitch: detune, master tune, tuning, oscillator ratios. A note's frequency is fixed when it starts. Moving it live would mean routing it through pitch bend, which would change the sound even with the knob set before the note.
• Anything built into a waveform when the note starts: pulse-width tables, ring-modulation depth tables, waveform and wavetable choices, string models (Karplus pluck position and damping).
• Tremolo and ring-mod rates (Rhodes, Wurlitzer, CP-70, B3 Leslie, CS-80, DX7): synthio takes a ring frequency as a plain number, not something that can move.
• Layers that are off when the note starts. A layer whose mix is at zero isn't sounded at all, to save the voice. Its mix macro reaches a held note while that layer is sounding, but turning it up from zero brings it in on the next note. The same goes for a vibrato or wah whose depth was at zero when the note started: its rate and depth follow the knob only once it is there.
• Drum machines (all twelve kits): hits are short, and every macro already reaches the next hit.

Per instrument

Instrument	Live on held notes	Next note
andromeda	Volume, Filter 1/2 Cutoff, Filter Mix, Resonance 1/2, Env 1 -> F1/F2	Unison Detune, envelopes, Master Tune
arp2600	Volume, VCF Cutoff, Resonance, FM Amount*, Reverb Mix* (level; tail length is set at the note)	Osc 2/3 Detune, envelopes, Master Tune
b3	Volume, Drawbars 16/8/4/2*, Perc Level*, Key Click*, Overdrive	Perc Decay, Leslie Fast (ring rate), Master Tune
clavinet	Volume, Pickup Mix, Brilliance, Wah Depth*, Wah Rate*	Mute Level, envelopes, Master Tune
cp70	Volume, Hammer Strike, String Body, Brilliance	Tremolo Rate (ring rate), Tremolo Depth (table), Chorus (detune), Decay, Master Tune
cs80	Volume, VCF Cutoff, Resonance, HPF Cutoff, Layer II Mix, Brilliance	Ring Mod Speed (ring rate), Ring Mod Depth (table), Poly AT Depth (next pressure message), envelopes
cz101	Volume, PD Env Depth, Resonance, Vibrato Rate*, Vibrato Depth*	PD Attack/Decay, envelopes, Master Tune
d50	Volume, Transient Mix*, Synth Mix*, Cutoff, Resonance	Transient Tune, Chorus (detune), envelopes, Master Tune
dx7	Volume, FM Amount, Feedback, Alg Mix, Brightness, Vibrato Depth*, Vibrato Rate*	Mod Ratio, envelope times, Tremolo Depth (table), Tremolo Rate (ring rate), Master Tune
emulator2	Volume, Breath Noise*, Tone Brilliance, Filter Env, Vibrato Rate*, Vibrato Depth*	envelopes, Master Tune
fairlight	Volume, Bitcrush Approx (crushed layer*), Filter Env	Patch Select, envelopes, Pitch Env Depth, Master Tune
farfisa	Volume, Bass, Strings, Flute, Oboe, Trumpet (each*), Vibrato Rate*, Vibrato Depth*	Multi-Tone Booster (switches tables and filter mode), Master Tune
fs1r	Volume, FM Index*, Brightness	Vowel A/B, Morph Speed, envelopes, Master Tune
jp8000	Volume, Cutoff, Resonance, Supersaw Mix, Env Depth, HPF Cutoff	Supersaw Detune, Chorus (stereo spread), envelopes, Master Tune
juno106	Volume, Cutoff, Resonance, Sub Level, Noise Level*, Chorus Rate*, HPF, LFO Rate, Env Depth	Chorus Depth (also detune and on/off), PWM Amount (table), envelopes
jupiter8	Volume, Cutoff, Resonance, Env Depth, Cross Mod*, LFO Rate, HPF Cutoff	Unison, PW (table), envelopes
k2600	Volume, Layer 1-4 Mix*, Shimmer Delay*, Master Cutoff, Master Resonance, Mod Wheel*, Modulation Rate*, Modulation Depth*	envelopes, Master Tune
karplus	Volume, Body Resonance	Pluck Position, String Damping (string table), Pick Hardness (gone in 70 ms), Decay, Master Tune
mellotron	Volume, Tone, Flutter Rate*, Flutter Depth*, Tape Hiss	Attack, Release, Master Tune
microwave	Volume, Wavetable Pos, Cutoff, Resonance, Env to WT, Env to Filter	Filter Attack, envelopes, Master Tune
minimoog	Volume, Cutoff, Resonance, Env Amount, Noise Mix*, Overdrive	Glide, Osc2/Osc3 Detune, envelopes
ms20	Volume, HPF Cutoff, HPF Peak, LPF Cutoff, LPF Peak, EG2 Sweep, Noise Level*	Osc2 Pitch, Ring Mod (table), envelopes, Master Tune
ms2000	Volume, Cutoff, Resonance, Mod Seq Rate*, Mod Seq Depth*, Distortion*	Osc Waveform, envelopes, Master Tune
music_easel	Volume, Timbre Wavefold, FM Index*, Mod Osc Freq*	LPG Strike, LPG Decay, envelopes, Master Tune
nord_lead	Volume, Cutoff, Resonance, Morph 1-3	FM Amount, Osc Sync, Morph 4 (oscillator ratio), envelopes
obxa	Volume, Cutoff, Resonance, Env Depth	Detune Spread, envelopes, Master Tune
odyssey	Volume, Cutoff, Resonance, LFO Rate, Env Sweep, HPF Cutoff	Ring Mod (table), Osc 2 Detune, Sync, Glide, envelopes, Master Tune
pianet	Volume, Mellow Tone, Vibrato Rate*, Vibrato Depth*	Pluck Attack (gone in 0.1 s), Decay Time, envelopes, Master Tune
polysix	Volume, Sub-Osc Level*, Cutoff, Resonance, Ensemble Depth*, PWM Rate	envelopes, Master Tune
ppg_wave	Volume, Wavetable Index, Cutoff, Resonance, Env Amount	envelopes, Detune, Master Tune
prophet5	Volume, Cutoff, Resonance, Env Amount, LFO Rate, LFO Depth	Poly Mod, Osc2 Detune, Sync, envelopes
prophet_vs	Volume, Joystick X/Y*, Cutoff, Resonance, Env Amount, Chorus*	envelopes, Master Tune
rhodes	Volume, Tine Level, Body Level, Overdrive, Tone	Tremolo Rate (ring rate), Tremolo Depth (table), envelopes, Key-Off Noise, Master Tune
sh101	Volume, Sub-Osc Level, Cutoff, Resonance, Env Depth	Pulse Width (table), Fast Decay, Master Tune
solina	Volume, Violin/Viola/Cello Mix*, Chorus Depth	Attack, Release, Crescendo, Master Tune
taurus	Volume, Cutoff, Resonance, Env Mod	Osc B Detune, Beat Freq, Glide, envelopes, Master Tune
tb303	Volume, Cutoff, Resonance, Env Mod, Accent (level and envelope depth), Overdrive	Tuning, Decay, Master Tune; Accent's shorter decay is set at the note
virus	Volume, Sub Osc*, Cutoff, Resonance, Distortion, Env Depth	Hypersaw Detune, envelopes, Master Tune
vl1	Volume, Breath Pressure, Embouchure, Growl Rate*, Growl Depth*	envelopes, Master Tune
vox_continental	Volume, Drawbars 16/8/4/IV*, Vibrato Rate*, Vibrato Depth*, Brilliance	Master Tune
vp330	Volume, Male/Female Choir*, Bass*, Brilliance*, Chorus Depth*, Vibrato Rate*, Vibrato Depth*, Formant Shift	Attack, Release, Master Tune
wasp	Volume, Cutoff, Resonance, Noise Level*	Filter Mode, envelopes, Master Tune
wurlitzer	Volume, Bite, Bark	Tremolo Rate (ring rate), Tremolo Depth (table), envelopes, Master Tune

* Live while its layer, LFO or wah is sounding; one that was off when the note started comes in on the next note.

Where a filter releases through its own sweep after note-off (arp2600, ms20, prophet_vs), the release follows Cutoff and Resonance too. Breath on the VL1 now stays live after pressure, where pressure used to freeze the filter for the rest of the note.

How it works

_support.live(value) gives a macro one shared synthio.Math block. Every note wires that block into its filter frequency, Q, amplitude or LFO, and the macro handler writes block.a. gain() multiplies blocks for amplitudes that combine macros with velocity. note_is_silent(), which voice stealing uses, now reads a live amplitude's current value.

Tests

tests/test_live_macros.py holds a note on each instrument, moves each live macro to 0 and to 127, and asserts the held note comes out differently. Against the previous code it fails 244 of its 246 cases; the two that already passed are Mellotron's Volume and Tape Hiss, whose shared hiss note already followed the knob.

The instrument, API, polyphony, scheduling, sequencer, tempo-follow, shared-circuit and reset tests pass, as does tools/validate_api.py.