Sequencer Audio — Stereo Master Bus & Strip Chains

Handles all Web Audio API graph construction: the stereo master bus (glue compressor, send returns, per-channel limiters), per-strip audio chains (volume → saturation → compressor → filter → EQ → panner), and the Ruina + Reverb send effects. Extracted from the main sequencer.js to isolate AudioContext-dependent code.

Files

static/js/synth/sequencer-audio.js (427 lines)

Stereo Master Bus

strips (mono → StereoPanner → L/R)
    ↓
_mergeL ─┐
         ├→ ChannelMerger(2) → _masterGain → _glueComp (stereo-linked DN)
_mergeR ─┘                                         ↓
                                              ChannelSplitter(2)
                                              ├→ _limSumL ──→ _limiterL ──→ ┐
                                              └→ _limSumR ──→ _limiterR ──→ ├→ ChannelMerger(2) → destination
                                                                             ↑
       reverb.outputL ──→ _limSumL                                           │
       reverb.outputR ──→ _limSumR                                           │
       ruina.output(ch0) → _limSumL                                          │
       ruina.output(ch1) → _limSumR                                          │

Built by ensureMasterBus(engine, ac): - _mergeL/_mergeR — GainNodes receiving all strip outputs - _masterGain — master volume control - _glueComp — single DynamicsCompressorNode processing stereo (linked gain reduction) - _limSumL/_limSumR — summing junctions post-glue, pre-limiter where send returns inject - _limiterL/_limiterR — per-channel brickwall limiters (-6 dB, 20:1) - Final ChannelMerger(2) ensures proper stereo mapping to destination

Strip Audio Chain

Built by initStripAudio(engine, stripId, ac?):

eqHigh → StereoPanner → ChannelSplitter(2)
           └→ _mergeL (channel 0)
           └→ _mergeR (channel 1)

Each strip chain (mono throughout):

volGain → duckGain → saturator (WaveShaper)
    → compBypass/compressor → makeupGain
    → filter → filterBypass
    → eqLow → eqMid → eqHigh
    → StereoPanner → _mergeL / _mergeR

Strip compressor routing

When compressor.amount > 0.01, the chain routes through the compressor with auto makeup gain. The routing is tracked via chain._compRouted / _lastCompAmt to avoid unnecessary disconnect/reconnect cycles.

StereoPanner

Each strip has a StereoPannerNode (mono → stereo). Its L channel connects to _mergeL, R channel to _mergeR. Pan is controlled by strip.pan (−1 to +1).

Send Effects

Reverb

_playNote → revG (gain = sends.reverb) → _reverbInput → reverbNode.input
    → reverbNode.outputL → _limSumL
    → reverbNode.outputR → _limSumR

Ruina

_playNote → ruinaG (gain = sends.ruina) → _ruinaInput → ruinaNode.input
    → ruinaNode.output → ChannelSplitter(2)
        → ch0 → _limSumL
        → ch1 → _limSumR

Offline Rendering

Two functions support explicit AudioContext for WAV export:

`buildOfflineMaster(engine, ac, includeSends)`

Creates a full stereo master bus in an OfflineAudioContext. Returns { mergeL, mergeR, limSumL, limSumR, reverbNode, ruinaNode }.

`buildOfflineStripChain(strip, ac)`

Creates a strip's audio chain in an explicit AudioContext without storing on the engine. Returns all nodes for immediate use. No side effects.

Exports

Export	Signature	Purpose
`buildSaturationCurve`	`(amount, len)`	Float32Array tanh waveshaper curve
`ensureMasterBus`	`(engine, ac)`	Creates stereo master bus on first call
`initStripAudio`	`(engine, stripId, ac?)`	Creates strip chain, skips if exists; `ac` optional for offline
`updateStripAudio`	`(engine, stripId)`	Updates vol/solo/mute, saturator, compressor routing, filter, EQ, pan
`buildOfflineMaster`	`(engine, ac, includeSends)`	Async — master bus for offline render
`buildOfflineStripChain`	`(strip, ac)`	Strip chain for offline render

Channel Count Pattern

StereoPannerNode and ruina output GainNode may not report 2 output channels at connect() time. The pattern used throughout is:

var splitter = ac.createChannelSplitter(2);
panner.connect(splitter);
splitter.connect(destL, 0, 0);  // ch0 → L
splitter.connect(destR, 1, 0);  // ch1 → R

ChannelSplitterNode always has exactly numberOfOutputs outputs regardless of input channel count.