Beat Tracking

In order to synchronize the LEDs with the music, we are running real-time beat tracking in the server.

diagram

At a high level, the flow of the signal is:

  1. Record audio samples with a US microphone (controlled by PortAudio)
  2. PortAudio then calls our callback with a buffer of 512 frames. Note: this call back is a realtime callback and very sensitive to any delays. We thus run it in it’s dedicated thread.
  3. We then push the buffer to a synchronized queue.
  4. The Beat Detector, which runs in a separate thread, pops the buffer and runs another cycle of the beat tracking algorithm. We are relying on Adam Stark’s BTrack library. We found it to be one of the most efficient realtime trackers. Given its lack of C++ support and separation of concerns, we rewrote the library in the spirit of Essentia, with small bricks of composable elements, chained in a pipeline.
  5. The Beat Detector then send the update tempo and beat timing to the Broadcast which broadcasts it of UDP to all Pico boards on the network.

diagram