Implement procedural drum synthesis based on DSP research

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 +42,42 @@ 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 a white noise buffer.
+ * @param context - Tone Audio Context
+ * @param duration - Duration in seconds (default 2.0)
+ */
+export function generateWhiteNoise(context: Tone.BaseContext, duration: number = 2.0): AudioBuffer {
+    const sampleRate = context.sampleRate;
+    const bufferSize = 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;
+}
+
+/**
+ * Generates a 15-bit LFSR (Linear Feedback Shift Register) noise buffer.
+ * Emulates the digital "crunch" of vintage drum machines like the TR-909.
+ * @param context - Tone Audio Context
+ * @param duration - Duration in seconds (default 2.0)
+ */
+export function generateLFSRNoise(context: Tone.BaseContext, duration: number = 2.0): AudioBuffer {
+    const sampleRate = context.sampleRate;
+    const bufferSize = sampleRate * duration;
+    const buffer = context.createBuffer(1, bufferSize, sampleRate);
+    const data = buffer.getChannelData(0);
+
+    let reg = 0x7FFF; // 15-bit register
+    for (let i = 0; i < bufferSize; i++) {
+        // LFSR 15-bit: bit 14 and 13 (0-indexed bits 14 and 13 are usually used for 15-bit)
+        // Common 15-bit LFSR taps: bits 14 and 13
+        let bit = ((reg >> 0) ^ (reg >> 1)) & 1;
+        reg = (reg >> 1) | (bit << 14);
+        data[i] = (reg & 1) ? 1 : -1;
+    }
+    return buffer;
+}

src/logic/drums/TR808Clap.ts

@@ -1,17 +1,17 @@
 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(), 2.0);
     }
 
     trigger(time: number, pitch: number, decay: number, velocity: number = 0.8) {
+        if (velocity <= 0) return;
+
+        const randomStart = Math.random() * (this.noiseBuffer.duration - 0.6);
         const noiseSrc = new Tone.BufferSource(this.noiseBuffer);
         const bpfFreq = (1000 + pitch * 1000);
         const bpf = new Tone.Filter(applyVariance(bpfFreq, 0.02), "bandpass");
@@ -20,26 +20,28 @@ export class TR808Clap {
         noiseSrc.connect(bpf);
         bpf.connect(gain);
 
+        const safeVelocity = Math.max(0.001, velocity);
+
         // Triple attack "snaps"
         const snapCount = 3;
         const snapIntervalBase = 0.01;
         const snapInterval = applyVariance(snapIntervalBase, 0.02);
 
         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.setValueAtTime(safeVelocity, snapTime);
+            gain.gain.exponentialRampToValueAtTime(safeVelocity * 0.1, snapTime + snapInterval * 0.8);
         }
 
         // Final decay
         const finalDecayStart = time + snapCount * snapInterval;
         const decayTimeBase = 0.1 + decay * 0.5;
         const decayTime = applyVariance(decayTimeBase, 0.02);
 
-        gain.gain.setValueAtTime(velocity, finalDecayStart);
+        gain.gain.setValueAtTime(safeVelocity, finalDecayStart);
         gain.gain.exponentialRampToValueAtTime(0.001, finalDecayStart + decayTime);
 
-        noiseSrc.start(time).stop(finalDecayStart + decayTime);
+        noiseSrc.start(time, randomStart).stop(finalDecayStart + decayTime);
 
         noiseSrc.onended = () => {
             noiseSrc.dispose();

src/logic/drums/TR808Cowbell.ts

@@ -2,11 +2,13 @@ import * as Tone from 'tone'
 import { applyPitchDrift, applyVariance } from '../DrumUtils'
 
 export class TR808Cowbell {
-    private activeGains: Set<Tone.Gain> = new Set();
+    private activeVoices: Set<{ oscillators: Tone.Oscillator[], vca: 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
@@ -30,10 +32,12 @@ export class TR808Cowbell {
 
         const decayTime = applyVariance(0.1 + decay * 0.4, 0.02);
 
-        vca.gain.setValueAtTime(velocity, time);
+        const safeVelocity = Math.max(0.001, velocity);
+        vca.gain.setValueAtTime(safeVelocity, time);
         vca.gain.exponentialRampToValueAtTime(0.001, time + decayTime);
 
-        this.activeGains.add(vca);
+        const voice = { oscillators: [osc1, osc2], vca };
+        this.activeVoices.add(voice);
 
         osc1.start(time).stop(time + decayTime);
         osc2.start(time).stop(time + decayTime);
@@ -45,15 +49,18 @@ export class TR808Cowbell {
             bpf.dispose();
             hpf.dispose();
             vca.dispose();
-            this.activeGains.delete(vca);
+            this.activeVoices.delete(voice);
         };
     }
 
     stop(time: number) {
-        this.activeGains.forEach(vca => {
-            vca.gain.cancelScheduledValues(time);
-            vca.gain.exponentialRampToValueAtTime(0.001, time + 0.02);
+        this.activeVoices.forEach(voice => {
+            voice.vca.gain.cancelScheduledValues(time);
+            voice.vca.gain.exponentialRampToValueAtTime(0.001, time + 0.02);
+            voice.oscillators.forEach(osc => {
+                osc.stop(time + 0.02);
+            });
         });
-        this.activeGains.clear();
+        this.activeVoices.clear();
     }
 }

src/logic/drums/TR808HiHat.ts

@@ -3,11 +3,13 @@ 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();
+    private activeVoices: Set<{ oscillators: Tone.Oscillator[], envGain: 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");
@@ -48,17 +50,19 @@ export class TR808HiHat {
         const decayTime = applyVariance(decayBase, 0.02);
 
         // VCA Envelope
-        envGain.gain.setValueAtTime(velocity, time);
+        const safeVelocity = Math.max(0.001, velocity);
+        envGain.gain.setValueAtTime(safeVelocity, time);
         envGain.gain.exponentialRampToValueAtTime(0.001, time + decayTime);
 
-        this.activeGains.add(envGain);
+        const voice = { oscillators, 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
+        // Disposal - Explicitly clean up all nodes to prevent memory leaks
         // We use the first oscillator's onstop event to trigger the cleanup
         oscillators[0].onstop = () => {
             oscillators.forEach(o => o.dispose());
@@ -67,15 +71,18 @@ export class TR808HiHat {
             bpf2.dispose();
             envGain.dispose();
             hpf.dispose();
-            this.activeGains.delete(envGain);
+            this.activeVoices.delete(voice);
         };
     }
 
     stop(time: number) {
-        this.activeGains.forEach(gain => {
-            gain.gain.cancelScheduledValues(time);
-            gain.gain.exponentialRampToValueAtTime(0.001, time + 0.02);
+        this.activeVoices.forEach(voice => {
+            voice.envGain.gain.cancelScheduledValues(time);
+            voice.envGain.gain.exponentialRampToValueAtTime(0.001, time + 0.02);
+            voice.oscillators.forEach(osc => {
+                osc.stop(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 +25,26 @@ 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
+        // Two-stage frequency sweep as per memories
         const startFreq = tuneDrift * 2.5;
+        const midFreq = tuneDrift * 1.2;
         const endFreq = tuneDrift;
 
         osc.frequency.setValueAtTime(startFreq, time);
+        osc.frequency.exponentialRampToValueAtTime(midFreq, time + 0.02);
         osc.frequency.exponentialRampToValueAtTime(endFreq, time + 0.05);
 
-        // VCA Amp Envelope: Instant attack, adjustable exponential decay
-        masterGain.gain.setValueAtTime(velocity, time);
-        masterGain.gain.exponentialRampToValueAtTime(0.001, time + finalDecay);
+        // VCA Amp Envelope: Instant attack, two-stage decay (damping)
+        // Damping stage: fast 20ms initial decay to 50% volume emulating diode behavior
+        const safeVelocity = Math.max(0.001, velocity);
+        masterGain.gain.setValueAtTime(safeVelocity, time);
+        masterGain.gain.exponentialRampToValueAtTime(safeVelocity * 0.5, time + 0.02);
+
+        // Final decay
+        const safeFinalDecay = Math.max(0.05, 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(), 2.0);
     }
 
     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;
 
@@ -40,13 +36,15 @@ export class TR808Snare {
 
         // Independent envelopes for maximum authenticity as per research
         // High mode decays faster (approx 75% of low mode decay)
-        gainLow.gain.setValueAtTime(velocity * (1 - toneBalance), time);
+        const safeVelocity = Math.max(0.001, velocity);
+        gainLow.gain.setValueAtTime(safeVelocity * (1 - toneBalance), time);
         gainLow.gain.exponentialRampToValueAtTime(0.001, time + vcaDecay);
 
-        gainHigh.gain.setValueAtTime(velocity * toneBalance, time);
+        gainHigh.gain.setValueAtTime(safeVelocity * toneBalance, time);
         gainHigh.gain.exponentialRampToValueAtTime(0.001, time + vcaDecay * 0.75);
 
         // Snappy Layer
+        const randomStart = Math.random() * (this.noiseBuffer.duration - 0.5);
         const noiseSrc = new Tone.BufferSource(this.noiseBuffer);
         // High-pass filter (>1800Hz) to prevent phase trap with tonal body
         // Q = 0.707 (Butterworth)
@@ -61,12 +59,12 @@ export class TR808Snare {
         noiseFilter.connect(snappyGain);
         snappyGain.connect(this.destination);
 
-        snappyGain.gain.setValueAtTime(velocity * 0.8, time);
+        snappyGain.gain.setValueAtTime(safeVelocity * 0.8, time);
         snappyGain.gain.exponentialRampToValueAtTime(0.001, time + snappyDecay);
 
         oscLow.start(time).stop(time + vcaDecay);
         oscHigh.start(time).stop(time + vcaDecay);
-        noiseSrc.start(time).stop(time + snappyDecay + 0.1);
+        noiseSrc.start(time, randomStart).stop(time + snappyDecay + 0.1);
 
         // Cleanup
         oscLow.onstop = () => {

src/logic/drums/TR909Kick.ts

@@ -1,5 +1,5 @@
 import * as Tone from 'tone'
-import { makeDistortionCurve, applyPitchDrift, applyVariance } from '../DrumUtils'
+import { makeDistortionCurve, applyPitchDrift, applyVariance, generateWhiteNoise } from '../DrumUtils'
 
 export class TR909Kick {
     private noiseBuffer: AudioBuffer;
@@ -8,17 +8,12 @@ export class TR909Kick {
     constructor(private destination: Tone.ToneAudioNode) {
         // Soft Clipping curve from research
         this.bodyCurve = makeDistortionCurve(10);
-
-        const sampleRate = Tone.getContext().sampleRate;
-        const bufferSize = sampleRate * 0.05; // 50ms click
-        this.noiseBuffer = Tone.getContext().createBuffer(1, bufferSize, sampleRate);
-        const data = this.noiseBuffer.getChannelData(0);
-        for (let i = 0; i < bufferSize; i++) {
-            data[i] = Math.random() * 2 - 1;
-        }
+        this.noiseBuffer = generateWhiteNoise(Tone.getContext(), 2.0);
     }
 
     trigger(time: number, pitch: number, decay: number, velocity: number = 0.8) {
+        if (velocity <= 0) return;
+
         // 909 Kick base frequency is fixed around 50Hz
         const tune = 50;
         // The 'Pitch' parameter on 909 maps to the frequency sweep duration
@@ -53,10 +48,12 @@ export class TR909Kick {
         bodyOsc.frequency.exponentialRampToValueAtTime(endFreq, time + sweepDuration);
 
         // VCA Envelope
-        bodyGain.gain.setValueAtTime(velocity, time);
+        const safeVelocity = Math.max(0.001, velocity);
+        bodyGain.gain.setValueAtTime(safeVelocity, time);
         bodyGain.gain.exponentialRampToValueAtTime(0.001, time + vcaDecay);
 
         // Click Layer (Noise)
+        const randomStart = Math.random() * (this.noiseBuffer.duration - 0.1);
         const noiseSrc = new Tone.BufferSource(this.noiseBuffer);
         const noiseFilter = new Tone.Filter(noiseFilterFreq, "highpass"); // HPF > 1kHz to avoid phase trap
         const noiseGain = new Tone.Gain(0);
@@ -67,7 +64,7 @@ export class TR909Kick {
 
         // Ultra short envelope (10-20ms) for the click
         const clickDecay = applyVariance(0.02, 0.02);
-        noiseGain.gain.setValueAtTime(velocity * 0.7, time);
+        noiseGain.gain.setValueAtTime(safeVelocity * 0.7, time);
         noiseGain.gain.exponentialRampToValueAtTime(0.001, time + clickDecay);
 
         // Rectangular Pulse Click: Short 5ms impulse for attack articulation
@@ -76,11 +73,11 @@ export class TR909Kick {
         pulseOsc.connect(pulseGain);
         pulseGain.connect(this.destination);
 
-        pulseGain.gain.setValueAtTime(velocity * 0.5, time);
+        pulseGain.gain.setValueAtTime(safeVelocity * 0.5, time);
         pulseGain.gain.exponentialRampToValueAtTime(0.001, time + 0.005);
 
         bodyOsc.start(time).stop(time + vcaDecay);
-        noiseSrc.start(time).stop(time + clickDecay);
+        noiseSrc.start(time, randomStart).stop(time + clickDecay);
         pulseOsc.start(time).stop(time + 0.005);
 
         bodyOsc.onstop = () => {