WebAudio Engine

MixiEngine

Singleton audio engine at 44,100 Hz. See Architecture for the complete signal chain.

Memory Management

• Buffer limit: 200 MB max per session
• Node pooling: AudioBufferSourceNode instances are stopped, disconnected, and dereferenced after use
• Waveform cache: Analyzed waveform data cached after first analysis to avoid re-computation

Audio Analysis Queue

Track analysis (waveform, BPM, key) is serialized via a queue to avoid hitting the browser's limit of ~6 concurrent OfflineAudioContext instances.

Wasm DSP Bridge

Optional Rust/WebAssembly signal chain running entirely on the audio thread.

Initialization

1. Check SharedArrayBuffer + Atomics support (requires COOP/COEP headers)
2. Register AudioWorklet processor (mixi-dsp-worklet.js)
3. Create 2-input worklet node (Deck A = input 0, Deck B = input 1)
4. Create shared buffers (audio ring + param bus + metering bus)
5. Fetch and compile Wasm module
6. Send compiled module to worklet via postMessage
7. Wait for ready confirmation (5 second timeout, fallback to native WebAudio)

Shared Memory Layout

Buffer	Size	Direction	Purpose
audioRing	32,776 bytes	Main → Worklet	SPSC ring buffer (~93 ms at 44.1 kHz)
paramBus	512 bytes	Bidirectional	All DSP parameters (see below)
meteringBus	28 bytes	Worklet → Main	7 floats: peakL, rmsL, peakR, rmsR, masterPeak, masterRms, limiterGR

Parameter Bus Layout (512 bytes)

Per-Deck (bytes 0–127 for A, 128–255 for B):

Offset	Parameter	Default
+0	Trim	1.0
+4	EQ Low	0 dB
+8	EQ Mid	0 dB
+12	EQ High	0 dB
+16	Fader	1.0
+20	Crossfader Gain	(computed)
+24	Color FX Frequency	Hz
+28	Color FX Resonance	Q
+32	CUE Active	0/1
+36	Playback Rate	1.0
+40–96	FX params (filter, delay, reverb, phaser, flanger, gate)	per-FX

Master (bytes 256–383):

Offset	Parameter	Default
256	Gain	1.0
260	Filter	0 (bypass)
264	Distortion	0
272	Punch	0
280	Limiter Active	1
284	Limiter Threshold	-1 dB

Global (bytes 384–511):

Offset	Parameter
384	Crossfader position
388	Crossfader curve (0=smooth, 1=sharp, 2=constant)
392	Headphone mix
396	Headphone level
400	Sample rate
508	Layout version (must match Rust)

DSP Modules in Wasm

The Rust engine implements the full signal chain:

• 3-band EQ (per deck)
• Color FX filter (per deck)
• Per-deck FX: Filter, Delay, Reverb, Phaser, Flanger, Gate
• Master: Gain, Filter, Distortion, Punch compressor, Limiter
• Crossfader with 3 curve types
• Headphone/CUE monitoring
• Auto-gain per deck
• Metering: per-channel peak/RMS, master peak/RMS, limiter gain reduction

Opt-in

The Wasm DSP path defaults to off. Enable it in Settings. When active, it bypasses the native WebAudio EQ/FX/MasterBus nodes entirely.

AudioWorklets

Worklet	File	Purpose
mixi-dsp-processor	mixi-dsp-worklet.js	Full Rust/Wasm signal chain
diode-ladder-processor	diode-ladder-processor.js	TurboBass 4-pole diode ladder filter
recording-tap	recording-tap.js	Disk recording bridge (WAV, crash-proof)

Recording

Format

WAV, 32-bit float PCM, stereo, 44,100 Hz. Tapped post-limiter from master bus output.

Architecture

Crash-proof ring buffer design:

• 131,072 frames capacity (~3 seconds)
• Fixed ~1 MB RAM regardless of recording length
• Flush interval: 500 ms
• Temp file survives crashes; orphan recovery available

Features

• Start/stop/cancel
• Save As via native dialog
• Cue marks during recording
• Orphan recovery for crashed sessions

Electron Only

Recording requires the Electron desktop app with SharedArrayBuffer support.