The Recorder — the tap, the file, the library

The Recorder taps the master output and writes it to a lossless WAV file. One button to start, one button to stop. It's how you capture takes, render arrangement variations, and round-trip sound design (record a DSP → re-import as a sample → use in another DSP).

This section covers the signal model and what lands on disk; the next section covers the workflows + the MCP catalog.

#The signal tap

The Recorder is registered in the routing table as an audio Sink named recorder-default. Its bus consumes master:out — the same signal your speakers receive, after the master FX rack, after the master volume, after the softclip stage.

That means:

• Everything you hear, you record — every Builder, every sequencer-driven instrument, every send return, the lot.
• A muted track is silent in the recording too — mute / solo on the Mixer is a real take-management tool.
• Master FX affects the recording — the reverb tail, the saturator drive, the softclip protection. The recording captures the master signal AS-RENDERED, not the pre-fader sources.

If you want to record ONE source dry (e.g. a Builder without master FX), three options:

1. Solo its mixer track during the take — simplest. Master FX still applies; everything else is silent.
2. Solo + disable master FX slots — master.fx.slot.enabled.set { slot_id, enabled: false } per slot during the take. Dry source, no master colour.
3. Direct route to the Recorder — routing.connect { from_source: <builder-id>, to_sink: "recorder-default", kind: "audio" }. The default master → recorder-default cable stays; you add a second cable that bypasses the master entirely. Sum-into-recorder if you don't disconnect the master cable; pure-source if you do.

See FaustWave — Patchbay § 4 for the routing.* primitives, FaustWave — Mixer & Master § 2 for the FX-rack actions.

#The Rec button

Four ways to start / stop a recording, all driving the same underlying state:

1. Master Transport Widget Rec button — the red dot near the right end of the topbar widget, immediately left of the Panic button. Pulses red while recording. Click to start; click again to stop.
2. Recorder rail panel toggle — same control, plus the recordings library on the panel body.
3. MCP — recorder.start, recorder.stop, recorder.toggle.
4. AI Assistant — "record the next loop pass" routes through the same recorder.toggle action.

All four sync to one underlying recorderState Svelte store — click the rail panel button while a chain is firing recorder.toggle and you'll see the panel flip even though the press came from elsewhere.

#What gets written

32-bit float is lossless within the AudioContext's processing range — no clip distortion in the file even if the master meter shows red (the softclip kicks in earlier; the file captures the softclipped signal). About 12 MB per minute stereo at 48 kHz, so a long take is big but pristine.

For sharing, transcode to 16-bit or 24-bit FLAC via ffmpeg / Audacity:

# 24-bit FLAC, lossless, ~2-3× smaller than 32-bit float WAV
ffmpeg -i 2026-06-07T08-46-22_abc123.wav -c:a flac -sample_fmt s32 output.flac

#Where the files live

Electron's standard userData location — same place your projects + node-packs + Logto session live. The Recorder rail panel has a Reveal button per recording that opens the OS file manager directly at the file.

#The recordings library

The Recorder rail panel lists every recording ever made, newest first. Each row carries:

• Name — the timestamped filename.
• Duration in seconds.
• Size on disk.
• Three action buttons:
  • Play — in-app preview via the audio system, independent of the master transport.
  • Reveal — open the file in the OS file manager.
  • Delete — hard-delete. No trash (greenfield discipline) — the file is gone the moment you click. Confirm with care.

For AI & automation · MCP

recordings.list returns the library. recordings.play { recording_id } plays one. recordings.delete { recording_id } removes one. Use recordings.list to discover ids.

#A library-introspection chain

actions:
  - action_id: surface.open
    input: { surface: recorder-default }
    label: "▶ 0. Open the Recorder panel"
  - action_id: recordings.list
    input: {}
    save_as: lib
    label: "▶ 1. List existing recordings"
  - action_id: recorder.start
    input: {}
    label: "▶ 2. Start a new recording"
  - action_id: recorder.stop
    input: {}
    save_as: rec
    label: "■ 3. Stop + finalize (returns the WAV path)"

#State observability

The Recorder does NOT expose a state-snapshot MCP action of its own. Two ways to introspect:

• Observable state — the rail panel + the Rec button stay in sync because they subscribe to recorderState. If the panel says "recording", the Recorder is recording.
• Library is the audit log — every Stop writes a row to the library; recordings.list is the historical record. Compare two recordings.list snapshots to detect what landed between them.

Next section: the workflows — the 30-second take, round-trip into the sample store, the live-perf capture pattern.