[linux-audio-user] Firewire devices and Linux

Pieter Palmers pieterp at joow.be
Sat May 13 09:19:07 EDT 2006


Paul Winkler wrote:
> On Fri, May 12, 2006 at 06:32:01PM +0200, Pieter Palmers wrote:
> 
>>Paul Winkler wrote:
>>
>>>(re. presonus Firepod latency)... what kind of latency are you getting
>>>with it?
>>>
>>
>>The current freebob code + recent firmware should give you around 
>>350frames of latency at 44100/48000 (about 7ms). Round trip including AD 
>>/ DA, measured using jdelay.
> 
> 
> Not bad at all!
> I haven't measured with jdelay, but if I understand correctly,
> round-trip latency is d + (p + p*n)/sr, where p is the -p
> arg to the jackd backend, n is the -n argument, sr is the sampling rate,
> and d is the latency introduced by DA and AD conversions.
> 
> Assuming d is about 1-2 ms, that means you're running with
> something like jackd -d alsa ... -p 64 -n 3 
> or -p 64 -n 2 ?
-p 64 -n 3

> 
> If so, that's really pretty nice, I haven't done any better
> on my delta 66 (but I haven't tried aggressively to go lower).
> I can sort of run at -p 32 -n 3 (3ms + d) but I get dropouts.
> 

You need a very well tuned system in order for the -p64 -n3 setup to 
work without dropouts though, and even then... We are working on 
improving the ieee1394 kernel support in order to improve this.

Pieter


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