Interface Microphone

Interface — Microphone: Calibration & Tuner

The microphone panel groups two tools that use audio input from an ALSA capture device:

1. Latency Calibrator — measures the round-trip delay of each instrument and writes the result directly into that instrument's sync_delay field.
2. Chromatic Tuner — detects the pitch of any sound and guides you to a target note.

Source: public/js/features/CalibrationModal.js, public/js/features/TunerModal.js, src/audio/DelayCalibrator.js.

Latency Calibration

How It Works

1. Général Midi Boop sends a probe note to the instrument.
2. ALSA records the audio response on the selected input.
3. Onset detection finds the first amplitude peak above the threshold.
4. round-trip delay = audio onset timestamp − note send timestamp.
5. Steps 1–4 repeat N times; the median is used as the final value.
6. A confidence score is derived from the spread of measurements (tight cluster = high confidence).
7. The delay is written to instrument_settings.sync_delay; playback compensation applies immediately.

ALSA Device Selection

Field	Description
Device	ALSA capture device (e.g. hw:1,0, default, sysdefault)
Auto-detect	Picks the first detected USB microphone automatically

Any device listed by arecord -l is available in the dropdown.

VU Meter & Threshold

A real-time level bar shows the microphone input. An inline draggable threshold slider sets the onset detection level (0.01–0.10 of full scale). Verify that:

• The bar rises when the instrument plays.
• The bar stays below the threshold when the instrument is silent.

A threshold set too high will miss soft onsets; too low will trigger on background noise.

Per-Instrument Measurement

Each connected instrument has its own "Measure" button and a status indicator:

Status	Meaning
idle	No measurement taken yet
running	Measurement in progress
success	Valid result, delay and confidence shown
error	No onset detected or inconsistent results

Run measurements independently so that instruments with very different latencies are each calibrated correctly.

Chart

A canvas chart plots the round-trip delay and confidence score across all runs for the selected instrument. Use this to spot outliers or environmental noise spikes.

Tunables

Parameter	Default	Description
Number of measurements	5	Median calculated over N runs
Detection threshold	0.05	Onset amplitude threshold
Probe note	A4 (69)	MIDI note sent to trigger the instrument
Probe velocity	100	Velocity of the probe note

Apply Delays Button

Once at least one measurement succeeds, an "Apply delays" button appears. It writes all pending latency values in one operation. Individual instruments can also be applied one at a time.

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Chromatic Tuner

The tuner is accessible via the "Open Tuner" link at the top of the calibration panel (or directly from the device panel). Pitch detection runs server-side using the MPM algorithm; the frontend subscribes to tuner:pitch WebSocket events.

Operating Modes

Mode	Description
Auto	No target — detects the nearest chromatic note and displays the cents deviation
Note	User selects a target note from a chromatic strip (E1–C6); needle shows up/down guidance
Instrument	User selects a connected instrument; for strings the open-string notes are shown; for other instruments falls back to the chromatic row

Auto Mode

Play any note; the display locks onto the closest pitch and shows cents deviation (−50 to +50 cents). Useful for quick intonation checks without a specific target.

Note / Instrument Mode

Select a target note or open string. The needle and colour indicator guide you:

• Green — within ±5 cents (in tune)
• Yellow — 5–20 cents deviation
• Red — >20 cents deviation

Built-In Instrument Presets (Open Strings)

Preset	Open strings
Guitar	E2 A2 D3 G3 B3 E4
Bass	E1 A1 D2 G2
Violin	G3 D4 A4 E5
Viola	C3 G3 D4 A4
Cello	C2 G2 D3 A3
Ukulele	G4 C4 E4 A4

Note names follow the locale format set in Interface-Settings (US notation, solfège, or raw MIDI number). Reference pitch: A4 = 440 Hz.

Related Pages

• Interface-Instrument-Creation — latency sync_delay is stored per instrument
• Interface-Settings — select note-name locale (US / solfège / MIDI number)
• Advanced-Topics — technical background on onset detection and the MPM algorithm