Rundown: Web Audio API effects feasibility for LittleJS

[Copilot]

The issue asks to investigate hooking up audio effects (reverb, filter, etc.) via the Web Audio API. This is a research/analysis pass — no code changes yet.

Current signal chain

AudioBufferSourceNode → StereoPannerNode → GainNode (per-sound) → audioMasterGain → destination

audioContext and audioMasterGain are already public, so insertion points exist at both master and per-sound level.

Feasible additions

Master bus (global, affects all sounds)

• DynamicsCompressorNode — prevents clipping; near-zero config; strong candidate for core
• BiquadFilterNode — LPF/HPF for "muffled" effects (underwater, wall, etc.)
• ConvolverNode — room reverb via impulse response (file-based or synthetically generated)

Per-sound (on individual SoundInstance)

• BiquadFilterNode — per-sound EQ (telephone voice, muffled footstep)
• DelayNode + feedback — echo/slap-back
• WaveShaperNode — distortion/overdrive
• PannerNode (3D) — upgrade from flat StereoPannerNode; adds distance model, cone, orientation

Utilities

• Synthetic reverb IR generator (exponential noise decay — no audio file needed)
• connectMasterEffect(node) escape hatch for custom Web Audio graphs

Proposed placement

Scope	Location
Master compressor / filter / reverb	src/engineAudio.js, wired in audioInit() with setter functions
Per-sound filter / delay	Sound class, optional param or method
Optional/complex effects	New plugins/audioEffects.js

Master DynamicsCompressorNode is small enough to belong in core. Everything else is a clean fit for a plugin.