12 Jan
2009
12 Jan
'09
4:37 p.m.
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