Improved song sync 2.0 now with even more improvement

[polson]

Song sync improvements

This improves song synchronization to be faster and more accurate. Works with a 5000ms buffer without oscillation.

In addition we fix meteronome sync to line up more accurately with the beatlines with a new BassOneShotChannel class. This class uses a DSP to schedule the playback of a pre-loaded oneshot sample (ie metronome sound). It also handles the rescheduling necessary upon time and tempo changes. We also introduce a MetronomeScheduler class that schedules these all at once.

• Tested on macOS and Windows with multiple buffer sizes and song speeds.
• Both macOS and Windows give 0 ms audio calibration when playing on a device keyboard, which indicates that measurements are correct on both platforms.
  Linux testing TBD.

Example video with 2000 ms buffer

CleanShot.2026-07-11.at.17.29.42.mp4

Changes

• Sync correction now runs on the main unity thread. This greatly reduces complexity and prevents deadlock issues. Testing ensures that sync still works correctly even at 5 fps and 1000ms buffer size.
• Song sync accuracy is now to 1.5 ms with a new algorithm based on a Smith-predictor
• Song seek and resume also now lands much closer to the target, so only a small tempo adjustment is required to sync up after these events. Sometimes no tempo adjustment is needed.
• Metronome now runs perfectly in sync with the beatlines