Authentic TR-808/909 Drum Synthesis Engine

src/logic/DrumUtils.ts

@@ -1,3 +1,5 @@
+import * as Tone from 'tone'
+
 /**
  * Shared DSP utilities for drum synthesis based on research specs.
  */
@@ -40,3 +42,38 @@ export function applyVariance(base: number, variance: number = 0.02): number {
     // Math.random() * 0.04 - 0.02 gives range [-0.02, 0.02]
     return base * (1 + (Math.random() * (variance * 2) - variance));
 }
+
+/**
+ * Generates an authentic 15-bit LFSR noise buffer (TR-909 style).
+ * Characteristic polynomial: x^15 + x^14 + 1
+ */
+export function generateLFSRNoise(context: Tone.BaseContext): AudioBuffer {
+    const sampleRate = context.sampleRate;
+    const bufferSize = sampleRate * 2.0; // 2 seconds
+    const buffer = context.createBuffer(1, bufferSize, sampleRate);
+    const data = buffer.getChannelData(0);
+
+    let lfsr = 0x7FFF; // Initial state
+
+    for (let i = 0; i < bufferSize; i++) {
+        // Tap bits 14 and 15 (indices 13 and 14)
+        const bit = ((lfsr >> 14) ^ (lfsr >> 13)) & 1;
+        lfsr = ((lfsr << 1) | bit) & 0x7FFF;
+        data[i] = (bit * 2 - 1) * 0.5;
+    }
+    return buffer;
+}
+
+/**
+ * Generates a standard white noise buffer.
+ */
+export function generateWhiteNoise(context: Tone.BaseContext, duration: number = 2.0): AudioBuffer {
+    const sampleRate = context.sampleRate;
+    const bufferSize = Math.floor(sampleRate * duration);
+    const buffer = context.createBuffer(1, bufferSize, sampleRate);
+    const data = buffer.getChannelData(0);
+    for (let i = 0; i < bufferSize; i++) {
+        data[i] = Math.random() * 2 - 1;
+    }
+    return buffer;
+}

src/logic/drums/TR808Clap.ts

@@ -1,17 +1,16 @@
 import * as Tone from 'tone'
-import { applyVariance } from '../DrumUtils'
+import { applyVariance, generateWhiteNoise } from '../DrumUtils'
 
 export class TR808Clap {
     private noiseBuffer: AudioBuffer;
 
     constructor(private destination: Tone.ToneAudioNode) {
-        const sampleRate = Tone.getContext().sampleRate;
-        this.noiseBuffer = Tone.getContext().createBuffer(1, sampleRate * 0.5, sampleRate);
-        const data = this.noiseBuffer.getChannelData(0);
-        for (let i = 0; i < data.length; i++) data[i] = Math.random() * 2 - 1;
+        this.noiseBuffer = generateWhiteNoise(Tone.getContext());
     }
 
     trigger(time: number, pitch: number, decay: number, velocity: number = 0.8) {
+        if (velocity <= 0) return;
+
         const noiseSrc = new Tone.BufferSource(this.noiseBuffer);
         const bpfFreq = (1000 + pitch * 1000);
         const bpf = new Tone.Filter(applyVariance(bpfFreq, 0.02), "bandpass");
@@ -28,7 +27,7 @@ export class TR808Clap {
         for (let i = 0; i < snapCount; i++) {
             const snapTime = time + i * snapInterval;
             gain.gain.setValueAtTime(velocity, snapTime);
-            gain.gain.exponentialRampToValueAtTime(velocity * 0.1, snapTime + snapInterval * 0.8);
+            gain.gain.exponentialRampToValueAtTime(Math.max(0.001, velocity * 0.1), snapTime + snapInterval * 0.8);
         }
 
         // Final decay
@@ -39,7 +38,9 @@ export class TR808Clap {
         gain.gain.setValueAtTime(velocity, finalDecayStart);
         gain.gain.exponentialRampToValueAtTime(0.001, finalDecayStart + decayTime);
 
-        noiseSrc.start(time).stop(finalDecayStart + decayTime);
+        const randomStart = Math.random() * (this.noiseBuffer.duration - decayTime - 0.2);
+        noiseSrc.start(time, randomStart);
+        noiseSrc.stop(finalDecayStart + decayTime + 0.1);
 
         noiseSrc.onended = () => {
             noiseSrc.dispose();

src/logic/drums/TR808Cowbell.ts

@@ -2,14 +2,16 @@ import * as Tone from 'tone'
 import { applyPitchDrift, applyVariance } from '../DrumUtils'
 
 export class TR808Cowbell {
-    private activeGains: Set<Tone.Gain> = new Set();
+    // Track active voices for clean termination
+    private activeVoices: Set<{ oscillators: Tone.Oscillator[], gain: Tone.Gain }> = new Set();
 
     constructor(private destination: Tone.ToneAudioNode) { }
 
     trigger(time: number, pitch: number, decay: number, velocity: number = 0.8) {
+        if (velocity <= 0) return;
+
         // Core: Dual square wave oscillators from Schmitt trigger matrix
-        // Standard frequencies: 540Hz and 800Hz
-        const pitchMultiplier = 0.5 + pitch; // Range approx 0.5x to 1.5x
+        const pitchMultiplier = 0.5 + pitch;
         const freq1 = applyPitchDrift(540 * pitchMultiplier, 2.0);
         const freq2 = applyPitchDrift(800 * pitchMultiplier, 2.0);
 
@@ -33,27 +35,34 @@ export class TR808Cowbell {
         vca.gain.setValueAtTime(velocity, time);
         vca.gain.exponentialRampToValueAtTime(0.001, time + decayTime);
 
-        this.activeGains.add(vca);
+        const voice = { oscillators: [osc1, osc2], gain: vca };
+        this.activeVoices.add(voice);
 
         osc1.start(time).stop(time + decayTime);
         osc2.start(time).stop(time + decayTime);
 
-        osc1.onstop = () => {
+        const cleanup = () => {
             osc1.dispose();
             osc2.dispose();
             mixGain.dispose();
             bpf.dispose();
             hpf.dispose();
             vca.dispose();
-            this.activeGains.delete(vca);
+            this.activeVoices.delete(voice);
         };
+
+        osc1.onstop = cleanup;
+        setTimeout(cleanup, (decayTime + 0.1) * 1000);
     }
 
     stop(time: number) {
-        this.activeGains.forEach(vca => {
-            vca.gain.cancelScheduledValues(time);
-            vca.gain.exponentialRampToValueAtTime(0.001, time + 0.02);
+        this.activeVoices.forEach(voice => {
+            voice.oscillators.forEach(osc => {
+                osc.stop(time);
+            });
+            voice.gain.gain.cancelScheduledValues(time);
+            voice.gain.gain.exponentialRampToValueAtTime(0.001, time + 0.02);
         });
-        this.activeGains.clear();
+        this.activeVoices.clear();
     }
 }

src/logic/drums/TR808HiHat.ts

@@ -3,11 +3,14 @@ import { applyPitchDrift, applyVariance } from '../DrumUtils'
 
 export class TR808HiHat {
     private frequencies = [205.3, 304.4, 369.6, 522.7, 800, 540];
-    private activeGains: Set<Tone.Gain> = new Set();
+    // Track active voices for clean termination/choking
+    private activeVoices: Set<{ oscillators: Tone.Oscillator[], gain: Tone.Gain }> = new Set();
 
     constructor(private destination: Tone.ToneAudioNode) { }
 
     trigger(time: number, isOpen: boolean, pitch: number, decay: number, velocity: number = 0.8) {
+        if (velocity <= 0) return;
+
         // Create nodes
         const mixGain = new Tone.Gain(0.15);
         const bpf1 = new Tone.Filter(3440, "bandpass");
@@ -20,62 +23,64 @@ export class TR808HiHat {
 
         // Create 6 Square Wave Oscillators (Schmitt Trigger Matrix)
         const oscillators = this.frequencies.map(freq => {
-            const driftedFreq = applyPitchDrift(freq * pitchMultiplier, 2.0); // +/- 2Hz drift for hats
+            const driftedFreq = applyPitchDrift(freq * pitchMultiplier, 2.0);
             const osc = new Tone.Oscillator(driftedFreq, "square");
             osc.phase = Math.random() * 360;
             osc.connect(mixGain);
             return osc;
         });
 
         // Routing Graph
-        // Oscillators -> MixGain -> [BPF1, BPF2] (Parallel) -> EnvGain -> HPF -> Destination
         mixGain.connect(bpf1);
         mixGain.connect(bpf2);
         bpf1.connect(envGain);
         bpf2.connect(envGain);
         envGain.connect(hpf);
         hpf.connect(this.destination);
 
-        // Filter Q values and randomization
         bpf1.Q.value = 1.5;
         bpf2.Q.value = 1.5;
         bpf1.frequency.value = applyVariance(3440, 0.02);
         bpf2.frequency.value = applyVariance(7100, 0.02);
         hpf.frequency.value = applyVariance(7000, 0.02);
 
-        // Decay: Closed Hat (40-60ms), Open Hat (300-500ms)
         const decayBase = isOpen ? (0.3 + decay * 0.2) : (0.04 + decay * 0.02);
         const decayTime = applyVariance(decayBase, 0.02);
 
-        // VCA Envelope
         envGain.gain.setValueAtTime(velocity, time);
         envGain.gain.exponentialRampToValueAtTime(0.001, time + decayTime);
 
-        this.activeGains.add(envGain);
+        const voice = { oscillators, gain: envGain };
+        this.activeVoices.add(voice);
 
-        // Scheduling
         oscillators.forEach(osc => {
             osc.start(time).stop(time + decayTime);
         });
 
-        // Disposal - Explicitly clean up all 11-12 nodes to prevent memory leaks
-        // We use the first oscillator's onstop event to trigger the cleanup
-        oscillators[0].onstop = () => {
+        // Disposal and Cleanup
+        const cleanup = () => {
             oscillators.forEach(o => o.dispose());
             mixGain.dispose();
             bpf1.dispose();
             bpf2.dispose();
             envGain.dispose();
             hpf.dispose();
-            this.activeGains.delete(envGain);
+            this.activeVoices.delete(voice);
         };
+
+        // Use setTimeout as a safety net if onstop is not reliable in all environments
+        oscillators[0].onstop = cleanup;
+        setTimeout(cleanup, (decayTime + 0.1) * 1000);
     }
 
     stop(time: number) {
-        this.activeGains.forEach(gain => {
-            gain.gain.cancelScheduledValues(time);
-            gain.gain.exponentialRampToValueAtTime(0.001, time + 0.02);
+        this.activeVoices.forEach(voice => {
+            voice.oscillators.forEach(osc => {
+                osc.stop(time);
+            });
+            voice.gain.gain.cancelScheduledValues(time);
+            voice.gain.gain.exponentialRampToValueAtTime(0.001, time + 0.02);
         });
-        this.activeGains.clear();
+        this.activeVoices.clear();
     }
 }

src/logic/drums/TR808Kick.ts

@@ -5,6 +5,8 @@ export class TR808Kick {
     constructor(private destination: Tone.ToneAudioNode) { }
 
     trigger(time: number, pitch: number, decay: number, velocity: number = 0.8) {
+        if (velocity <= 0) return;
+
         // pitch: 0.5 -> 52.5Hz, maps to 45-60Hz range
         const tune = 45 + pitch * 15;
         // decay: 0.5 -> 1.7s, maps to 0.4-3.0s range
@@ -23,18 +25,23 @@ export class TR808Kick {
         const finalDecay = applyVariance(decayTime, 0.02);
 
         // Pitch Envelope: Start high (Tune * 2.5) and drop quickly (50ms) to simulate the membrane hit ('tonk')
-        // This rapid sweep generates the punch without needing a separate click oscillator
         const startFreq = tuneDrift * 2.5;
         const endFreq = tuneDrift;
 
         osc.frequency.setValueAtTime(startFreq, time);
         osc.frequency.exponentialRampToValueAtTime(endFreq, time + 0.05);
 
-        // VCA Amp Envelope: Instant attack, adjustable exponential decay
+        // VCA Amp Envelope with Diode Damping emulation
+        // Fast initial decay (20ms) to 50% volume followed by the main decay
+        const dampingTime = 0.02;
         masterGain.gain.setValueAtTime(velocity, time);
-        masterGain.gain.exponentialRampToValueAtTime(0.001, time + finalDecay);
+        masterGain.gain.exponentialRampToValueAtTime(velocity * 0.5, time + dampingTime);
+
+        // Ensure final decay is always longer than damping stage
+        const safeFinalDecay = Math.max(dampingTime + 0.01, finalDecay);
+        masterGain.gain.exponentialRampToValueAtTime(0.001, time + safeFinalDecay);
 
-        osc.start(time).stop(time + finalDecay);
+        osc.start(time).stop(time + safeFinalDecay);
 
         osc.onstop = () => {
             osc.dispose();

src/logic/drums/TR808Snare.ts

@@ -1,20 +1,16 @@
 import * as Tone from 'tone'
-import { applyPitchDrift, applyVariance } from '../DrumUtils'
+import { applyPitchDrift, applyVariance, generateWhiteNoise } from '../DrumUtils'
 
 export class TR808Snare {
     private noiseBuffer: AudioBuffer;
 
     constructor(private destination: Tone.ToneAudioNode) {
-        const sampleRate = Tone.getContext().sampleRate;
-        const bufferSize = sampleRate * 0.5; // 500ms
-        this.noiseBuffer = Tone.getContext().createBuffer(1, bufferSize, sampleRate);
-        const data = this.noiseBuffer.getChannelData(0);
-        for (let i = 0; i < data.length; i++) {
-            data[i] = Math.random() * 2 - 1;
-        }
+        this.noiseBuffer = generateWhiteNoise(Tone.getContext());
     }
 
     trigger(time: number, pitch: number, snappy: number, velocity: number = 0.8) {
+        if (velocity <= 0) return;
+
         // pitch maps to tone balance here (balance between low and high modes)
         const toneBalance = pitch;
 
@@ -49,7 +45,6 @@ export class TR808Snare {
         // Snappy Layer
         const noiseSrc = new Tone.BufferSource(this.noiseBuffer);
         // High-pass filter (>1800Hz) to prevent phase trap with tonal body
-        // Q = 0.707 (Butterworth)
         const noiseFilter = new Tone.Filter({
             frequency: noiseFilterFreq,
             type: "highpass",
@@ -64,9 +59,12 @@ export class TR808Snare {
         snappyGain.gain.setValueAtTime(velocity * 0.8, time);
         snappyGain.gain.exponentialRampToValueAtTime(0.001, time + snappyDecay);
 
+        const randomStart = Math.random() * (this.noiseBuffer.duration - snappyDecay - 0.1);
+        noiseSrc.start(time, randomStart);
+        noiseSrc.stop(time + snappyDecay + 0.1);
+
         oscLow.start(time).stop(time + vcaDecay);
         oscHigh.start(time).stop(time + vcaDecay);
-        noiseSrc.start(time).stop(time + snappyDecay + 0.1);
 
         // Cleanup
         oscLow.onstop = () => {