b1rdmania
5e127c3a3e
- Authentic DMG-CPU sound chip implementation: - 4 Pulse channels with duty cycle control (12.5%, 25%, 50%, 75%) - 2 Wave channels with 4-bit wavetables - 2 Noise channels with LFSR (7-bit and 15-bit modes) - GameBoy Colorizer effect chain: - Low-pass filter (natural GB rolloff) - Bit-crushing (4-bit DAC simulation) - Sample rate reduction - Saturation and high-pass filter - Presets: DMG, GBC, GBA, Clean - Intelligent MIDI processing: - Track analysis and role detection (bass, lead, drums, etc.) - Automatic channel mapping to GB channels - Chord arpeggiator for polyphony handling - GameBoy Arranger for fuller sound - BitMidi search integration - Completely isolated from v1 (no changes to src/)
83 lines
2.1 KiB
TypeScript
83 lines
2.1 KiB
TypeScript
/**
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* Game Boy Duty Cycle Implementation
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*
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* The GB pulse channels support 4 duty cycle patterns.
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* These exact duty ratios give the Game Boy its distinctive sound.
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*/
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/**
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* Duty cycle ratios for the 4 GB patterns
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* 12.5% - Very thin, buzzy, laser-like sound
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* 25% - Classic chiptune sound, bright and punchy
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* 50% - Full square wave
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* 75% - Same as 25% but inverted
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*/
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export const DUTY_RATIOS = [0.125, 0.25, 0.5, 0.75] as const;
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export type DutyIndex = 0 | 1 | 2 | 3;
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/**
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* Creates a PeriodicWave for Web Audio from a duty cycle.
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*
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* Uses proper Fourier series for pulse wave:
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* imag[n] = (2 / (π * n)) * sin(π * n * duty)
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*
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* This is the mathematically correct way to synthesize pulse waves.
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*/
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export function createDutyWave(
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dutyIndex: DutyIndex,
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audioContext: BaseAudioContext
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): PeriodicWave {
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const dutyRatio = DUTY_RATIOS[dutyIndex];
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// More harmonics = sharper edges (but more CPU)
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const numHarmonics = 64;
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const real = new Float32Array(numHarmonics);
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const imag = new Float32Array(numHarmonics);
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// DC offset = 0 for centered waveform
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real[0] = 0;
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imag[0] = 0;
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// Fourier series for pulse wave
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// https://en.wikipedia.org/wiki/Pulse_wave
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for (let n = 1; n < numHarmonics; n++) {
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// Pulse wave Fourier coefficient
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const coefficient = (2 / (Math.PI * n)) * Math.sin(Math.PI * n * dutyRatio);
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imag[n] = coefficient;
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real[n] = 0;
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}
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return audioContext.createPeriodicWave(real, imag, {
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disableNormalization: false
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});
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}
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/**
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* Pre-creates all 4 duty cycle waveforms for efficient reuse.
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*/
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export function createAllDutyWaves(
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audioContext: BaseAudioContext
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): PeriodicWave[] {
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return [
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createDutyWave(0, audioContext),
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createDutyWave(1, audioContext),
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createDutyWave(2, audioContext),
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createDutyWave(3, audioContext),
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];
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}
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/**
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* Returns a human-readable description of each duty cycle.
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*/
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export function getDutyDescription(dutyIndex: DutyIndex): string {
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const descriptions = [
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'12.5% - Thin, buzzy',
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'25% - Classic chiptune',
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'50% - Full square',
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'75% - Bright, punchy',
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];
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return descriptions[dutyIndex];
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}
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