This cdlc sometime have fluctuations in beatmap regarding of sounds, +-25 ms ( i look in EOF), so you getting notes on screen late (or early) on ~25 ms + a RScable have a latency ~15 (in good case), +output audio buffer ~15 + some your early(late) sound picking -10 ms(if you tried to get "perfect"), ->summary ~50 ms will not give a perfection. Check setting in RS about Display delay, adjust flashes for accuracy hit in beat And look ini file RS and try to setting a minimum count buffer and a size of buffers (depends of the audiocard or chip). My ini an example: LatencyBuffer=1 MaxOutputBufferSize=144