[RDD] RD 2.0

Fred Gleason fredg at paravelsystems.com
Thu Jul 8 09:01:44 EDT 2010


On Wednesday 07 July 2010 09:07:38 pm Aaron Jowitt wrote:
> 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.

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.


> It would be good to eliminate all segue 
> delay in RD for all audio devices, or at least for the ASI and 
> Axia/Logitek AoIP drivers (i have not tested this).

*All* is not a realistic goal: CPUs are inherently sequential devices, so no 
pure software solution will be able to achieve this.  A more reasonable goal 
would be to reduce it below the level of human audibility; research I've seen 
puts this threshold at about 5 mS.  An ASI setup can certainly comes close to 
or beat that standard (I've never formally measured it).  Axia AoIP *is* 
ALSA, so those constraints apply, although there you will be limited to a 
minimum 'PeriodSize=' value of 256 due to the design of the LiveWire protocol 
(240 PCM frames/packet for standard streams).  As for the Logitek stuff, I 
have no idea -- I've yet to see even a theoretical design of how that's 
supposed to work.

Cheers!


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| Frederick F. Gleason, Jr. |               Chief Developer               |
|                           |               Paravel Systems               |
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