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On Monday 12 January 2009, Giso Grimm wrote: > Hi all, > > in several audio devices I observe a minimal block size setting of 1 ms: > > - In the Echo Layla 3G, it is possible to configure smaller block sizes, > but the driver or device seems to use 3 fragments instead of 2. > > - With the RME HDSP9652, I hear artifacts when I configure a fragment > size which is smaller than 1 ms. > > - With the RME HDSP9632 I am not able to configure a smaller fragment > size at all. > > Does anyone know about the source of this mystic border? If it is in the > ALSA abstraction or driver layer, what is the reason for this? Is it > simply the assumption that nobody needs shorter fragment sizes, and > shorter fragment sizes are likely to produce xruns? Or is this just > caused by the hardware? Either the hardware or the driver. I have used sub-millisecond latencies (roundtrip) on a delta66 card and a properly setup -rt kernel without XRUNS. E.g. 8 frames per period, 2 periods at 48khz (2*8/48000 is ca 0.3ms latency). ALSA itself (the framework, not each and every device-specific driver) and jackd can handle these latencies just fine. Just as a sidenote: There is additional latency caused by the DA and AD converters themselfes which varies from device to device. I think Fons once released a program to measure these additional latencies.. I don't know the figures for the delta 66. Regards, Flo -- Palimm Palimm! http://tapas.affenbande.org |
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