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Fine tuning ALSA for your sound card

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Q: When I last checked out RD six months ago (DB and audio on playback pc, using M-Audio sound card and on board sound), there was a varying delay/gap when segueing - perhaps in the order of 50-150ms. Why is this?

A: Ah, ALSA. There are some tuning knobs in rd.conf(5) that could significantly improve this; specifically, see the 'PeriodSize=' parameter in the [Alsa] section. That file ships with a very conservative number for this setting so we don't xrun on setups with poor realtime performance. Lowering it will reduce playout latency at the cost of demanding better RT performance. At some point as you lower it, you'll start getting xruns (often audible, but can also be seen in the syslog); you generally want this set at a value just above that point. On well-tuned hardware with a preemptive kernel and an ICE2712-based card, I've been able to get this as low as 64 frames/period.

Frederick F. Gleason, Jr.

Chief Developer

Paravel Systems

For more information also see Wiki page: Garbled audio, alsa error 32: Broken pipe, Xrun errors