message: annotating type
diff: @@ -301,7 +301,7 @@ export class TickSource<TypeName extends "bpm" | "hertz"> extends ToneWithContex
  lastStateEvent = event;
  });
  - let error = null;
  + let error: Error | null = null;
  if (lastStateEvent && lastStateEvent.state === "started") {
  const maxStartTime = Math.max(lastStateEvent.time, startTime);
  