12. MIDI

MIDI latency

Every MIDI instrument takes a moment to send a note: a keyboard a few milliseconds, a MIDI guitar’s converter often 20 to 40, as it works out the pitch. Stab takes each device’s latency off what it plays, so a note you played on the beat is recorded on the beat, and practice that listens judges you on what you played rather than on the cable.

Calibrating MIDI latency

Available on every platform.

Calibrating

1. Plug the device in, and put the caret where the song can play a few bars.
2. Choose Calibrate MIDI Latency (the Transport menu or the Transport pane › Record), or Calibrate on the device’s card in the MIDI In tab of the Audio & MIDI pane.
3. The song plays from the caret with the metronome on. Play a note on each click; a pill over the pane counts them (“Play on the click: 3 of 8”).
4. After eight notes on the beat, the latency is set. Stop the song, and the pill says what it is (“MIDI latency set to 24 ms”).

The first device you play is the one calibrated. Notes more than 150 ms from a click, and those played during a count-in, don’t count; the latency is the middle of the eight, so one stray note doesn’t spoil it. Choose the command again, or press Escape, to stop. It’s greyed while recording, and when no MIDI device has been seen.

Setting it by hand

Each device’s latency is also a setting: the latency chip on its card in the Audio & MIDI pane (0 to 100 ms), or the device’s Latency in Settings › Audio & MIDI. Calibrating can set up to 250 ms. It’s kept with the device, for every song.

What it changes

• Recording, Capture and practice (Wait for Me, Listen, Follow Me) take each note that much earlier.
• What you hear live doesn’t change: the instrument sounds as its notes arrive.

What you hear live

What you hear from a MIDI instrument, or from an Instrument pane, also waits for the audio output to take the next block of sound. With Audio Buffer on Auto (Settings › Audio & MIDI), Stab keeps that block short while a MIDI device is connected and on, an Instrument pane is open, or an audio track is armed or monitored: about 3 ms at 48 kHz instead of about 11. A fixed size there stays as you set it.In a browser, the browser sets that block; Stab asks for its shortest.

MIDI destinations have a latency of their own, the time a synth or module takes to sound, set in the MIDI Out tab: see MIDI out and clock. The audio input has its own too, measured by the speakers and the microphone: see The audio input.