Spectralite BPM Sync
The input, controls, OSC messages, MIDI clock and Outputs window of Spectralite BPM Sync for Mac.
Spectralite BPM Sync listens to an audio input on your Mac and sends its tempo and beat to other software. It needs macOS 12 or later.
Input
Press the input name at the top of the main screen to choose from the audio inputs your Mac offers. The app remembers your choice and mixes all channels of the chosen input into one. Press START to listen. If macOS has not allowed the microphone, the display reads NO MIC and START opens the system's privacy settings.
While BPM Sync listens, your Mac does not go to sleep, and the beat keeps its timing when the window is minimised or covered by other windows.
Controls
| Key | What it does |
|---|---|
| ÷2, ×2 | Moves the locked tempo down or up an octave. Use them when the tracker settles on half or double the tempo you feel. |
| CUE ALIGN | Press it on the downbeat. The nearest beat becomes the first beat of the bar, and BPM Sync adjusts its latency to your press. |
| RESET | Listens afresh, clearing the displays and the cue offset. |
| SYNC | Opens the Outputs window. |
The two keys on the top-left bumper close and minimise the window. Drag the device by its body to move it.
Outputs
The Outputs window has one section for each output, each with its own switch, and BPM Sync keeps the settings between launches. Each output also has an Offset field in milliseconds, from -1000 to 1000, that sends the output earlier when positive and later when negative. Use it to cover the receiving software's own delay.
OSC
OSC is off until you switch it on. It sends over UDP to the Host and Port you set, 127.0.0.1 and 7000 by default. Every address starts with the Prefix, /bpmsync by default, and the Messages list in the window shows them all.
| Address | Value | Sent |
|---|---|---|
/bpmsync/beat | Integer 1 to 4, the beat within the bar | On every beat |
/bpmsync/phase | Float 0 to 1, the position within the beat | 100 times a second |
/bpmsync/bar | Float 0 to 4, the position within the bar | 100 times a second |
/bpmsync/bpm | Float, the tempo | When it changes by 0.01 BPM, and each second |
/bpmsync/confidence | Float 0 to 1 | When it changes by 0.01, and each second |
/bpmsync/lock | Integer, 1 while locked and 0 otherwise | When it changes, and each second |
The lock message reports 0 when there is no tempo, and after 10 seconds without music.
MIDI clock
MIDI clock sends 24 pulses per quarter note. By default it goes to the app's own virtual MIDI source, which other apps on the Mac list as an input. Choose a different Port to send to a connected device. The list reads No MIDI ports when none is available and Not connected when a port you chose has disappeared.
Start and Stop is on by default. With it on, BPM Sync sends MIDI Start on the first bar line once it has a tempo and Stop when listening stops. Cue Align moves the bar, so it sends Stop and then Start on the next bar line.
Ableton Link
Ableton Link is coming soon, pending Ableton's licence.