Authentic TR-808 and TR-909 Drum Synthesis Implementation

src/logic/DrumUtils.ts

@@ -21,13 +21,14 @@ export function makeDistortionCurve(amount: number = 20): Float32Array {
 }
 
 /**
- * Applies micro-randomization to a base frequency (Pitch Drift).
- * Typically +/- 1Hz as per research.
+ * Applies micro-randomization to a base frequency (Pitch Drift) using cents.
+ * Typically +/- 1-2 cents as per research.
  * @param base - Base frequency in Hz
- * @param range - Drift range in Hz (default 1.0)
+ * @param centsRange - Drift range in cents (default 2.0)
  */
-export function applyPitchDrift(base: number, range: number = 1.0): number {
-    return base + (Math.random() * 2 - 1) * range;
+export function applyPitchDrift(base: number, centsRange: number = 2.0): number {
+    const cents = (Math.random() * 2 - 1) * centsRange;
+    return base * Math.pow(2, cents / 1200);
 }
 
 /**
@@ -37,6 +38,37 @@ export function applyPitchDrift(base: number, range: number = 1.0): number {
  * @param variance - Variance percentage (e.g. 0.02 for 2%)
  */
 export function applyVariance(base: number, variance: number = 0.02): number {
-    // Math.random() * 0.04 - 0.02 gives range [-0.02, 0.02]
+    // Math.random() * (variance * 2) - variance gives range [-variance, variance]
     return base * (1 + (Math.random() * (variance * 2) - variance));
 }
+
+/**
+ * Generates an authentic LFSR (Linear Feedback Shift Register) noise buffer.
+ * Emulates the 15-bit digital noise used in TR-909.
+ * Polynomial: x^15 + x^14 + 1
+ * @param context - AudioContext to create the buffer in
+ * @param duration - Duration in seconds
+ */
+export function generateLFSRNoise(context: any, duration: number = 0.5): AudioBuffer {
+    const sampleRate = context.sampleRate;
+    const bufferSize = sampleRate * duration;
+    const buffer = context.createBuffer(1, bufferSize, sampleRate);
+    const data = buffer.getChannelData(0);
+
+    let state = 0x7FFF; // 15-bit initial state (all ones)
+
+    for (let i = 0; i < bufferSize; i++) {
+        // Feedback bit = bit 14 XOR bit 13 (0-indexed bits of a 15-bit register)
+        const bit14 = (state >> 14) & 1;
+        const bit13 = (state >> 13) & 1;
+        const feedback = bit14 ^ bit13;
+
+        state = ((state << 1) | feedback) & 0x7FFF;
+
+        // Convert to [-1, 1] range
+        // We use bit 0 as the output bit
+        data[i] = ((state & 1) * 2) - 1;
+    }
+
+    return buffer;
+}

src/logic/drums/TR808Kick.ts

@@ -19,7 +19,7 @@ export class TR808Kick {
         masterGain.connect(this.destination);
 
         // Micro-randomization using shared utilities
-        const tuneDrift = applyPitchDrift(tune, 1.0);
+        const tuneDrift = applyPitchDrift(tune, 2.0); // +/- 2 cents
         const finalDecay = applyVariance(decayTime, 0.02);
 
         // Pitch Envelope: Start high (Tune * 2.5) and drop quickly (50ms) to simulate the membrane hit ('tonk')
@@ -30,11 +30,17 @@ export class TR808Kick {
         osc.frequency.setValueAtTime(startFreq, time);
         osc.frequency.exponentialRampToValueAtTime(endFreq, time + 0.05);
 
-        // VCA Amp Envelope: Instant attack, adjustable exponential decay
+        // VCA Amp Envelope: Two-stage decay to simulate diode damping
+        // 1. Initial fast decay to 50% over 20ms
+        // 2. Long exponential decay to zero
         masterGain.gain.setValueAtTime(velocity, time);
-        masterGain.gain.exponentialRampToValueAtTime(0.001, time + finalDecay);
+        masterGain.gain.exponentialRampToValueAtTime(velocity * 0.5, time + 0.02);
 
-        osc.start(time).stop(time + finalDecay);
+        // Ensure finalDecay is at least 0.021s to avoid scheduling errors
+        const safeFinalDecay = Math.max(finalDecay, 0.021);
+        masterGain.gain.exponentialRampToValueAtTime(0.001, time + safeFinalDecay);
+
+        osc.start(time).stop(time + safeFinalDecay);
 
         osc.onstop = () => {
             osc.dispose();

src/logic/drums/TR808Snare.ts

@@ -25,8 +25,8 @@ export class TR808Snare {
         const noiseFilterFreq = applyVariance(1800, 0.02);
 
         // 808 Membrane modes: fixed at ~238Hz and ~476Hz according to research
-        const oscLow = new Tone.Oscillator(applyPitchDrift(238, 1.0), "sine");
-        const oscHigh = new Tone.Oscillator(applyPitchDrift(476, 1.0), "sine");
+        const oscLow = new Tone.Oscillator(applyPitchDrift(238, 2.0), "sine"); // +/- 2 cents
+        const oscHigh = new Tone.Oscillator(applyPitchDrift(476, 2.0), "sine");
         oscLow.phase = Math.random() * 360;
         oscHigh.phase = Math.random() * 360;
 

src/logic/drums/TR909Kick.ts

@@ -28,7 +28,7 @@ export class TR909Kick {
         const decayTime = 0.3 + decay * 0.3;
 
         // Micro-randomization using shared utilities
-        const tuneDrift = applyPitchDrift(tune, 0.5);
+        const tuneDrift = applyPitchDrift(tune, 2.0); // +/- 2 cents
         const vcaDecay = applyVariance(decayTime, 0.02);
         const noiseFilterFreq = applyVariance(1000, 0.02);
 

src/logic/drums/TR909Snare.ts

@@ -1,5 +1,5 @@
 import * as Tone from 'tone'
-import { makeDistortionCurve, applyPitchDrift, applyVariance } from '../DrumUtils'
+import { makeDistortionCurve, applyPitchDrift, applyVariance, generateLFSRNoise } from '../DrumUtils'
 
 export class TR909Snare {
     private noiseBuffer: AudioBuffer;
@@ -9,14 +9,8 @@ export class TR909Snare {
         // Soft Clipping curve from research
         this.bodyCurve = makeDistortionCurve(15);
 
-        const sampleRate = Tone.getContext().sampleRate;
-        const bufferSize = sampleRate * 0.5;
-        this.noiseBuffer = Tone.getContext().createBuffer(1, bufferSize, sampleRate);
-        const data = this.noiseBuffer.getChannelData(0);
-        // While original used LFSR, research says Math.random() is sufficient for Web Audio API context
-        for (let i = 0; i < data.length; i++) {
-            data[i] = Math.random() * 2 - 1;
-        }
+        // Use authentic LFSR noise as per research for 909 Snare
+        this.noiseBuffer = generateLFSRNoise(Tone.getContext(), 0.5);
     }
 
     trigger(time: number, pitch: number, snappy: number, velocity: number = 0.8) {
@@ -29,8 +23,8 @@ export class TR909Snare {
         const snappyDecayBase = 0.1 + snappy * 0.4;
         const snappyDecay = applyVariance(snappyDecayBase, 0.02);
         const noiseHPFFreq = applyVariance(1000, 0.02);
-        const toneDrift1 = applyPitchDrift(freq1, 1.0);
-        const toneDrift2 = applyPitchDrift(freq2, 1.0);
+        const toneDrift1 = applyPitchDrift(freq1, 2.0); // +/- 2 cents
+        const toneDrift2 = applyPitchDrift(freq2, 2.0);
 
         const osc1 = new Tone.Oscillator(toneDrift1 * 2, "triangle");
         const osc2 = new Tone.Oscillator(toneDrift2 * 2, "triangle");

src/store/instrumentStore.ts

@@ -44,12 +44,13 @@ interface DrumState {
 }
 
 export const useDrumStore = create<DrumState>((set) => ({
-    kick: { steps: 16, pulses: 4, rotate: 0, decay: 0.5, pitch: 0.5, probability: 1.0 },
-    snare: { steps: 16, pulses: 2, rotate: 4, decay: 0.5, pitch: 0.5, probability: 1.0 },
-    hihat: { steps: 16, pulses: 12, rotate: 0, decay: 0.5, pitch: 0.5, probability: 1.0 },
-    hihatOpen: { steps: 16, pulses: 4, rotate: 2, decay: 0.5, pitch: 0.5, probability: 1.0 },
-    clap: { steps: 16, pulses: 2, rotate: 4, decay: 0.5, pitch: 0.5, probability: 1.0 },
-    cowbell: { steps: 16, pulses: 2, rotate: 2, decay: 0.5, pitch: 0.5, probability: 1.0 },
+    // Optimized Techno Foundation Patterns
+    kick: { steps: 16, pulses: 4, rotate: 0, decay: 0.5, pitch: 0.5, probability: 1.0 },     // 4-on-the-floor
+    snare: { steps: 16, pulses: 4, rotate: 4, decay: 0.5, pitch: 0.5, probability: 1.0 },    // Standard backbeat
+    hihat: { steps: 16, pulses: 12, rotate: 0, decay: 0.5, pitch: 0.5, probability: 1.0 },   // 16th notes / shuffle
+    hihatOpen: { steps: 16, pulses: 4, rotate: 2, decay: 0.5, pitch: 0.5, probability: 1.0 },// Off-beat hats
+    clap: { steps: 16, pulses: 2, rotate: 4, decay: 0.5, pitch: 0.5, probability: 1.0 },    // Occasional clap
+    cowbell: { steps: 16, pulses: 3, rotate: 2, decay: 0.5, pitch: 0.5, probability: 0.8 },  // Syncopated cowbell
     kit: '909',
     drive: 20,
     setParams: (drum, params) => set((state) => ({