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fix(midi): fade via expression and restore it with the voice's next note #2995

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Merged
Danielku15 merged 1 commit into from
Oct 29, 2026
Merged

fix(midi): fade via expression and restore it with the voice's next note #2995

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102 changes: 53 additions & 49 deletions packages/alphatab/src/midi/MidiFileGenerator.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -95,6 +95,7 @@ class PlayThroughContext {
export class MidiFileGenerator {
private static readonly _defaultDurationDead: number = 30;
private static readonly _defaultDurationPalmMute: number = 80;
private static readonly _fullExpression: number = 127;

private readonly _score: Score;
private _settings: Settings;
Expand All @@ -103,6 +104,7 @@ export class MidiFileGenerator {

private _currentTime: number = 0;
private _calculatedBeatTimers: Set<number> = new Set<number>();
private _fadedVoices: Set<string> = new Set<string>();

/**
* Gets a lookup object which can be used to quickly find beats and bars
Expand Down Expand Up @@ -143,6 +145,7 @@ export class MidiFileGenerator {
public generate(): void {
this.transpositionPitches.clear();
this._calculatedBeatTimers.clear();
this._fadedVoices.clear();
this._currentTime = 0;

// initialize tracks
Expand Down Expand Up @@ -757,6 +760,14 @@ export class MidiFileGenerator {
for (const automation of beat.automations) {
this._generateNonTempoAutomation(beat, automation, barStartTick);
}
const voiceKey = MidiFileGenerator._voiceKey(beat);
if (!beat.isRest && this._fadedVoices.has(voiceKey)) {
this._fadedVoices.delete(voiceKey);
// a fading beat sets the expression with its own ramp
if (beat.fade === FadeType.None) {
this._addExpression(track, barStartTick + beatStart, MidiFileGenerator._fullExpression);
}
}
if (beat.isRest) {
this._handler.addRest(track.index, barStartTick + beatStart, track.playbackInfo.primaryChannel);
} else if (beat.deadSlapped) {
Expand Down Expand Up @@ -1314,56 +1325,39 @@ export class MidiFileGenerator {
const track: Track = beat.voice.bar.staff.track;
switch (beat.fade) {
case FadeType.FadeIn:
this._generateFadeSteps(
track,
beatStart,
beatDuration,
0,
MidiFileGenerator._toChannelShort(track.playbackInfo.volume)
);
break;
this._generateFadeSteps(track, beatStart, beatDuration, 0, MidiFileGenerator._fullExpression);
return;
case FadeType.FadeOut:
this._generateFadeSteps(
track,
beatStart,
beatDuration,
MidiFileGenerator._toChannelShort(track.playbackInfo.volume),
0
);
this._generateFadeSteps(track, beatStart, beatDuration, MidiFileGenerator._fullExpression, 0);
break;
case FadeType.VolumeSwell:
const half = (beatDuration / 2) | 0;
this._generateFadeSteps(
track,
beatStart,
half,
0,
MidiFileGenerator._toChannelShort(track.playbackInfo.volume)
);
this._generateFadeSteps(
track,
beatStart + half,
half,
MidiFileGenerator._toChannelShort(track.playbackInfo.volume),
0
);

this._generateFadeSteps(track, beatStart, half, 0, MidiFileGenerator._fullExpression);
this._generateFadeSteps(track, beatStart + half, half, MidiFileGenerator._fullExpression, 0);
break;
}

// the expression is restored with the voice's next non-rest beat, so the release of the faded notes stays silent
this._fadedVoices.add(MidiFileGenerator._voiceKey(beat));
}

private static _voiceKey(beat: Beat): string {
const staff = beat.voice.bar.staff;
return `${staff.track.index}:${staff.index}:${beat.voice.index}`;
}

private _generateFadeSteps(
track: Track,
start: number,
duration: number,
startVolume: number,
endVolume: number
startExpression: number,
endExpression: number
): void {
const tickStep: number = 120;
// we want to reach the target volume a bit earlier than the end of the note
duration = (duration * 0.8) | 0;

const volumeFactor: number = (endVolume - startVolume) / duration;
const expressionFactor: number = (endExpression - startExpression) / duration;

const steps: number = (duration / tickStep + 1) | 0;
const endTick: number = start + duration;
Expand All @@ -1372,25 +1366,30 @@ export class MidiFileGenerator {
// ensure final value at end depending on rounding we might not reach it exactly
const isLast = i === steps - 1;
const tick: number = isLast ? endTick : start + i * tickStep;
const volume: number = isLast ? endVolume : Math.round(startVolume + (tick - start) * volumeFactor);

this._handler.addControlChange(
track.index,
tick,
track.playbackInfo.primaryChannel,
ControllerType.VolumeCoarse,
volume
);
this._handler.addControlChange(
track.index,
tick,
track.playbackInfo.secondaryChannel,
ControllerType.VolumeCoarse,
volume
);
const expression: number = isLast
? endExpression
: Math.round(startExpression + (tick - start) * expressionFactor);
this._addExpression(track, tick, expression);
}
}

private _addExpression(track: Track, tick: number, expression: number): void {
this._handler.addControlChange(
track.index,
tick,
track.playbackInfo.primaryChannel,
ControllerType.ExpressionControllerCoarse,
expression
);
this._handler.addControlChange(
track.index,
tick,
track.playbackInfo.secondaryChannel,
ControllerType.ExpressionControllerCoarse,
expression
);
}

private _generateVibrato(
note: Note,
noteStart: number,
Expand Down Expand Up @@ -2446,7 +2445,12 @@ export class MidiFileGenerator {

public generateSingleBeat(beat: Beat) {
const tempo = this.prepareSingleBeat(beat);
this._fadedVoices.clear();
this._generateBeat(beat, -beat.playbackStart /* to bring it to 0*/, beat.voice.bar, tempo);
if (this._fadedVoices.size > 0) {
this._fadedVoices.clear();
this._addExpression(beat.voice.bar.staff.track, beat.playbackDuration, MidiFileGenerator._fullExpression);
}
}

public generateSingleNote(note: Note) {
Expand Down
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