refactor(split): rename DeepDrftWeb -> DeepDrftPublic and DeepDrftWeb.Client -> DeepDrftPublic.Client (Phase 4)
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Daniel Harvey
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/**
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* SpectrumAnalyzer - Manages FFT analysis with filtering and slope correction.
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*
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* Single Responsibility: FFT analysis, frequency bucketing, and visual processing filters.
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*/
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export interface SpectrumConfig {
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bucketCount: number;
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highPassFreq: number; // Hz, 0 = disabled
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lowPassFreq: number; // Hz
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slopeDb: number; // dB/decade correction
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}
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export class SpectrumAnalyzer {
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private analyser: AnalyserNode | null = null;
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private audioContext: AudioContext | null = null;
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private fftSize: number = 2048;
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private dataArray: Float32Array<ArrayBuffer> | null = null;
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// Configuration
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private bucketCount: number = 32;
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private highPassFreq: number = 0;
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private lowPassFreq: number = 20000;
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private slopeDb: number = 0;
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// Animation state - supports multiple callbacks per player
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private animationId: number | null = null;
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private callbacks = new Map<string, (data: number[]) => void>();
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private lastFrameTime: number = 0;
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private targetFrameInterval: number = 1000 / 30; // ~30fps for smooth visuals without excessive interop
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initialize(context: AudioContext): AnalyserNode {
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this.audioContext = context;
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this.analyser = context.createAnalyser();
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this.analyser.fftSize = this.fftSize;
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this.analyser.smoothingTimeConstant = 0.8;
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this.dataArray = new Float32Array(this.analyser.frequencyBinCount);
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console.log(`SpectrumAnalyzer initialized: fftSize=${this.fftSize}, bins=${this.analyser.frequencyBinCount}`);
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return this.analyser;
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}
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getAnalyserNode(): AnalyserNode | null {
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return this.analyser;
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}
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setConfig(config: Partial<SpectrumConfig>): void {
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if (config.bucketCount !== undefined) this.bucketCount = config.bucketCount;
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if (config.highPassFreq !== undefined) this.highPassFreq = config.highPassFreq;
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if (config.lowPassFreq !== undefined) this.lowPassFreq = config.lowPassFreq;
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if (config.slopeDb !== undefined) this.slopeDb = config.slopeDb;
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}
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setHighPass(freq: number): void {
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this.highPassFreq = Math.max(0, freq);
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}
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setLowPass(freq: number): void {
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this.lowPassFreq = Math.max(20, freq);
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}
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setSlopeCorrection(dbPerDecade: number): void {
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this.slopeDb = dbPerDecade;
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}
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/**
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* Get frequency data as normalized values (0-1) for each bucket
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*/
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getFrequencyData(): number[] {
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if (!this.analyser || !this.dataArray || !this.audioContext) {
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return new Array(this.bucketCount).fill(0);
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}
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// Get raw FFT data (in dB, typically -100 to 0)
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this.analyser.getFloatFrequencyData(this.dataArray);
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const nyquist = this.audioContext.sampleRate / 2;
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const binCount = this.dataArray.length;
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const buckets: number[] = new Array(this.bucketCount).fill(0);
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// Logarithmic frequency mapping for perceptual balance
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// Map 20Hz - 20kHz to buckets using log scale
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const minFreq = 20;
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const maxFreq = Math.min(20000, nyquist);
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const logMin = Math.log10(minFreq);
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const logMax = Math.log10(maxFreq);
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const logRange = logMax - logMin;
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for (let bucket = 0; bucket < this.bucketCount; bucket++) {
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// Calculate frequency range for this bucket
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const logFreqLow = logMin + (bucket / this.bucketCount) * logRange;
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const logFreqHigh = logMin + ((bucket + 1) / this.bucketCount) * logRange;
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const freqLow = Math.pow(10, logFreqLow);
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const freqHigh = Math.pow(10, logFreqHigh);
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// Map frequencies to FFT bins
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const binLow = Math.floor((freqLow / nyquist) * binCount);
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const binHigh = Math.ceil((freqHigh / nyquist) * binCount);
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// Average the bins in this range
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let sum = 0;
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let count = 0;
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for (let bin = binLow; bin < binHigh && bin < binCount; bin++) {
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const freq = (bin / binCount) * nyquist;
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let value = this.dataArray[bin];
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// Apply filters
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value = this.applyFilters(value, freq);
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sum += value;
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count++;
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}
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const avgDb = count > 0 ? sum / count : -100;
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// Normalize from dB (-100 to 0) to 0-1 range
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// Clamp to reasonable range and scale
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const normalizedDb = Math.max(-80, Math.min(0, avgDb));
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buckets[bucket] = (normalizedDb + 80) / 80;
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}
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return buckets;
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}
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/**
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* Apply high-pass, low-pass, and slope correction filters
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*/
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private applyFilters(valueDb: number, freq: number): number {
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// Convert dB to linear for filter math
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let linear = Math.pow(10, valueDb / 20);
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// High-pass filter (6dB/octave)
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if (this.highPassFreq > 0 && freq < this.highPassFreq && freq > 0) {
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const octaves = Math.log2(this.highPassFreq / freq);
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const attenuation = Math.pow(10, (-6 * octaves) / 20);
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linear *= attenuation;
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}
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// Low-pass filter (6dB/octave)
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if (freq > this.lowPassFreq && this.lowPassFreq > 0) {
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const octaves = Math.log2(freq / this.lowPassFreq);
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const attenuation = Math.pow(10, (-6 * octaves) / 20);
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linear *= attenuation;
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}
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// Slope correction (dB/decade, referenced to 1kHz)
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if (this.slopeDb !== 0 && freq > 0) {
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const decades = Math.log10(freq / 1000);
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const correction = Math.pow(10, (this.slopeDb * decades) / 20);
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linear *= correction;
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}
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// Convert back to dB
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return linear > 0 ? 20 * Math.log10(linear) : -100;
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}
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/**
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* Add a callback for spectrum data. Starts animation loop on first subscriber.
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*/
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addCallback(id: string, callback: (data: number[]) => void): void {
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const wasEmpty = this.callbacks.size === 0;
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this.callbacks.set(id, callback);
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if (wasEmpty) {
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this.lastFrameTime = 0;
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this.animationId = requestAnimationFrame(this.animate);
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}
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}
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/**
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* Remove a callback by ID. Stops animation loop when no subscribers remain.
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*/
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removeCallback(id: string): void {
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this.callbacks.delete(id);
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if (this.callbacks.size === 0) {
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this.stopAnimation();
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}
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}
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/**
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* Stop animation loop
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*/
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stopAnimation(): void {
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if (this.animationId !== null) {
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cancelAnimationFrame(this.animationId);
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this.animationId = null;
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}
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}
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private animate = (timestamp: number): void => {
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if (this.callbacks.size === 0) return;
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// Throttle to target frame rate
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const elapsed = timestamp - this.lastFrameTime;
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if (elapsed >= this.targetFrameInterval) {
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this.lastFrameTime = timestamp - (elapsed % this.targetFrameInterval);
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const data = this.getFrequencyData();
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// Broadcast to all callbacks
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for (const cb of this.callbacks.values()) {
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cb(data);
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}
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}
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this.animationId = requestAnimationFrame(this.animate);
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};
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dispose(): void {
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this.stopAnimation();
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this.callbacks.clear();
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this.analyser = null;
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this.audioContext = null;
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this.dataArray = null;
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}
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}
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