fix: overlapping metronome channel (#2651)

Author: Danielku15

packages/alphatab/src/synth/AlphaSynth.ts

@@ -325,7 +325,7 @@ export class AlphaSynthBase implements IAlphaSynth {
         if (this._countInVolume > 0) {
             Logger.debug('AlphaSynth', 'Starting countin');
             this.sequencer.startCountIn();
-            this.synthesizer.setupMetronomeChannel(this._countInVolume);
+            this.synthesizer.setupMetronomeChannel(this.sequencer.metronomeChannel, this._countInVolume);
             this.updateTimePosition(0, true);
         }
 
@@ -340,7 +340,7 @@ export class AlphaSynthBase implements IAlphaSynth {
         }
 
         Logger.debug('AlphaSynth', 'Starting playback');
-        this.synthesizer.setupMetronomeChannel(this.metronomeVolume);
+        this.synthesizer.setupMetronomeChannel(this.sequencer.metronomeChannel, this.metronomeVolume);
         this._synthStopping = false;
         this.state = PlayerState.Playing;
         (this.stateChanged as EventEmitterOfT<PlayerStateChangedEventArgs>).trigger(
@@ -442,7 +442,7 @@ export class AlphaSynthBase implements IAlphaSynth {
 
     private _checkReadyForPlayback(): void {
         if (this.isReadyForPlayback) {
-            this.synthesizer.setupMetronomeChannel(this.metronomeVolume);
+            this.synthesizer.setupMetronomeChannel(this.sequencer.metronomeChannel, this.metronomeVolume);
             const programs = this.sequencer.instrumentPrograms;
             const percussionKeys = this.sequencer.percussionKeys;
             let append = false;
@@ -875,7 +875,7 @@ export class AlphaSynthAudioExporter implements IAlphaSynthAudioExporter {
     private _generatedAudioEndTime: number = 0;
 
     public setup() {
-        this._synth.setupMetronomeChannel(this._synth.metronomeVolume);
+        this._synth.setupMetronomeChannel(this._sequencer.metronomeChannel, this._synth.metronomeVolume);
 
         const syncPoints = this._sequencer.currentSyncPoints;
         const alphaTabEndTime = this._sequencer.currentEndTime;

packages/alphatab/src/synth/BackingTrackPlayer.ts

@@ -81,7 +81,7 @@ class BackingTrackAudioSynthesizer implements IAudioSampleSynthesizer {
         // not supported, ignore
     }
 
-    public setupMetronomeChannel(_metronomeVolume: number): void {
+    public setupMetronomeChannel(_metronomeChannel: number, _metronomeVolume: number): void {
         // not supported, ignore
     }
 

packages/alphatab/src/synth/IAudioSampleSynthesizer.ts

@@ -68,9 +68,10 @@ export interface IAudioSampleSynthesizer {
 
     /**
      * Configures the channel used to generate metronome sounds.
+     * @param metronomeChannel The midi hannel to use for playing the metronome (to avoid overlaps with instruments).
      * @param metronomeVolume The volume for the channel.
      */
-    setupMetronomeChannel(metronomeVolume: number): void;
+    setupMetronomeChannel(metronomeChannel: number, metronomeVolume: number): void;
 
     /**
      * Synthesizes the given number of samples without producing an output (e.g. on seeking)

packages/alphatab/src/synth/MidiFileSequencer.ts

@@ -51,6 +51,7 @@ class MidiSequencerState {
     public endTime: number = 0;
     public currentTempo: number = 0;
     public syncPointTempo: number = 0;
+    public metronomeChannel: number = SynthConstants.DefaultChannelCount - 1;
 }
 
 /**
@@ -65,6 +66,10 @@ export class MidiFileSequencer {
     private _oneTimeState: MidiSequencerState | null = null;
     private _countInState: MidiSequencerState | null = null;
 
+    public get metronomeChannel() {
+        return this._mainState.metronomeChannel;
+    }
+
     public get isPlayingMain(): boolean {
         return this._currentState === this._mainState;
     }
@@ -171,7 +176,7 @@ export class MidiFileSequencer {
                 const metronomeVolume: number = this._synthesizer.metronomeVolume;
                 this._synthesizer.noteOffAll(true);
                 this._synthesizer.resetSoft();
-                this._synthesizer.setupMetronomeChannel(metronomeVolume);
+                this._synthesizer.setupMetronomeChannel(this.metronomeChannel, metronomeVolume);
             }
             this._mainSilentProcess(timePosition);
         }
@@ -239,6 +244,8 @@ export class MidiFileSequencer {
         let metronomeTick: number = midiFile.tickShift; // shift metronome to content
         let metronomeTime: number = 0.0;
 
+        let maxChannel = 0;
+
         let previousTick: number = 0;
         for (const mEvent of midiFile.events) {
             const synthData: SynthEvent = new SynthEvent(state.synthData.length, mEvent);
@@ -287,6 +294,9 @@ export class MidiFileSequencer {
                 if (!state.firstProgramEventPerChannel.has(channel)) {
                     state.firstProgramEventPerChannel.set(channel, synthData);
                 }
+                if (channel > maxChannel) {
+                    maxChannel = channel;
+                }
                 const isPercussion = channel === SynthConstants.PercussionChannel;
                 if (!isPercussion) {
                     this.instrumentPrograms.add(programChange.program);
@@ -297,6 +307,9 @@ export class MidiFileSequencer {
                 if (isPercussion) {
                     this.percussionKeys.add(noteOn.noteKey);
                 }
+                if (noteOn.channel > maxChannel) {
+                    maxChannel = noteOn.channel;
+                }
             }
         }
 
@@ -314,6 +327,7 @@ export class MidiFileSequencer {
         });
         state.endTime = absTime;
         state.endTick = absTick;
+        state.metronomeChannel = maxChannel + 1;
 
         return state;
     }

packages/alphatab/src/synth/SynthConstants.ts

@@ -8,7 +8,6 @@
  */
 export class SynthConstants {
     public static readonly DefaultChannelCount: number = 16 + 1;
-    public static readonly MetronomeChannel: number = SynthConstants.DefaultChannelCount - 1;
     public static readonly MetronomeKey: number = 33;
     public static readonly AudioChannels: number = 2;
     public static readonly MinVolume: number = 0;

packages/alphatab/src/synth/synthesis/TinySoundFont.ts

@@ -63,6 +63,7 @@ export class TinySoundFont implements IAudioSampleSynthesizer {
     public currentTempo: number = 0;
     public timeSignatureNumerator: number = 0;
     public timeSignatureDenominator: number = 0;
+    private _metronomeChannel: number = SynthConstants.DefaultChannelCount - 1;
 
     public constructor(sampleRate: number) {
         this.outSampleRate = sampleRate;
@@ -188,8 +189,8 @@ export class TinySoundFont implements IAudioSampleSynthesizer {
         while (!this._midiEventQueue.isEmpty) {
             const m: SynthEvent = this._midiEventQueue.dequeue()!;
             if (m.isMetronome && this.metronomeVolume > 0) {
-                this.channelNoteOff(SynthConstants.MetronomeChannel, SynthConstants.MetronomeKey);
-                this.channelNoteOn(SynthConstants.MetronomeChannel, SynthConstants.MetronomeKey, 95 / 127);
+                this.channelNoteOff(this._metronomeChannel, SynthConstants.MetronomeKey);
+                this.channelNoteOn(this._metronomeChannel, SynthConstants.MetronomeKey, 95 / 127);
             } else if (m.event) {
                 this.processMidiMessage(m.event);
             }
@@ -204,7 +205,7 @@ export class TinySoundFont implements IAudioSampleSynthesizer {
                 // exception. metronome is implicitly added in solo
                 const isChannelMuted: boolean =
                     this._mutedChannels.has(channel) ||
-                    (anySolo && channel !== SynthConstants.MetronomeChannel && !this._soloChannels.has(channel));
+                    (anySolo && channel !== this._metronomeChannel && !this._soloChannels.has(channel));
 
                 if (!buffer) {
                     voice.kill();
@@ -261,18 +262,19 @@ export class TinySoundFont implements IAudioSampleSynthesizer {
     }
 
     public get metronomeVolume(): number {
-        return this.channelGetMixVolume(SynthConstants.MetronomeChannel);
+        return this.channelGetMixVolume(this._metronomeChannel);
     }
 
     public set metronomeVolume(value: number) {
-        this.setupMetronomeChannel(value);
+        this.setupMetronomeChannel(this._metronomeChannel, value);
     }
 
-    public setupMetronomeChannel(volume: number): void {
-        this.channelSetMixVolume(SynthConstants.MetronomeChannel, volume);
+    public setupMetronomeChannel(channel:number, volume: number): void {
+        this._metronomeChannel = channel;
+        this.channelSetMixVolume(channel, volume);
         if (volume > 0) {
-            this.channelSetVolume(SynthConstants.MetronomeChannel, 1);
-            this.channelSetPresetNumber(SynthConstants.MetronomeChannel, 0, true);
+            this.channelSetVolume(channel, 1);
+            this.channelSetPresetNumber(channel, 0, true);
         }
     }
 

packages/alphatab/test/audio/SyncPoint.test.ts

@@ -1,4 +1,9 @@
-import { type IEventEmitterOfT, type IEventEmitter, EventEmitterOfT, EventEmitter } from '@coderline/alphatab/EventEmitter';
+import {
+    type IEventEmitterOfT,
+    type IEventEmitter,
+    EventEmitterOfT,
+    EventEmitter
+} from '@coderline/alphatab/EventEmitter';
 import { ScoreLoader } from '@coderline/alphatab/importer/ScoreLoader';
 import { AlphaSynthMidiFileHandler } from '@coderline/alphatab/midi/AlphaSynthMidiFileHandler';
 import { MidiFile } from '@coderline/alphatab/midi/MidiFile';
@@ -464,7 +469,7 @@ class EmptyAudioSynthesizer implements IAudioSampleSynthesizer {
         _percussionKeys: Set<number>,
         _append: boolean
     ): void {}
-    public setupMetronomeChannel(_metronomeVolume: number): void {}
+    public setupMetronomeChannel(_metronomeChannel: number, _metronomeVolume: number): void {}
     public synthesizeSilent(_sampleCount: number): void {}
     public dispatchEvent(_synthEvent: SynthEvent): void {}
     public synthesize(_buffer: Float32Array, _bufferPos: number, _ampleCount: number): SynthEvent[] {