A beat whose whole job is QA: stereo-sync-beat renders 60 s of 120 BPM ping-pong — 1 kHz left-only ticks for Neo, 1.8 kHz right-only tocks for Blueberry, every 8th bar center-hitting both channels at 1.4 kHz — so the room's split play can be judged by ear: a limp in the ping-pong is machine-to-machine drift, a flam on the center bars is desync master