[linux-audio-dev] hdsp+latency questions

Thomas Charbonnel thomas at undata.org
Wed Feb 11 18:22:56 UTC 2004


d wrote:
> hello everyone!
> 
> this is not exactly about audio-development, but the DRI+jack thread 
> encouraged me to ask a few questions about optimizing my setup:
> i'm using a rme hdsp (cardbus) + multiface with my 1ghz pIII laptop for 
> quite a while now, and i'm happy with it.
> i would like to use the setup for live-processing but the lowest jackd 
> framesize i can safely use is 2048. the main issue here seems to be the 
> nvidia graphics card.
> since i switched from kernel 2.4.2x+lowlat+capabilities to 2.6.1 the 
> cpu-load seems to be noticable higher for ardour, but the latency-issue 
> did not change.
> so my questions are:
> 
> *) is anybody successfully using hdsp-cardbus with really low latencies ?

I'm using the same setup as you (hdsp+cardbus+1GHz PIII+nvidia binary 
drivers+2.6.1) and can use low latency without any problem. I use jack 
with the -R flag as a user thanks to Jack O'Quin's excellent 'realtime' 
module. Before that I used 2.4.x-ck and was also quite happy with it. 
The only latency killer apps I could identify at the time were 
applications accessing ACPI features (notably gnome's batstat applet). 
The ACPI situation has been much improved for me in the 2.6.x kernels 
(thanks to the CONFIG_ACPI_RELAXED_AML option - I have a toshiba laptop 
with a buggy BIOS)

> *) how important is the firmware version - which firmware version should 
> i use for my hdsp card?

Firmware version shouldn't change anything.

> *) did anyone else notice increasing cpu load with audio-apps + kernel 
> 2.6.x ?

I didn't.

> *) any hints about configuring X11 for linux-audio (besides from DRI 
> questions ;-) ?

You could try the open source nv driver that's shipped with X. You'll 
loose 3rd acceleration, though.

> 
> 
> let me know if you think i'm on the wrong list should better alsa-dev.
> 

I don't think for now that this is a driver issue, but can be wrong.
What version of alsa are you using ?
What happens when you run jack with period size < 2048 ? I guess jack 
reports xruns, but do they seem to appear regularly or randomly ? In 
your description you seem to imply that you do not have this latency 
problem when running without X, is it the case ? How low can you get 
running jack in text mode ? Generally speaking, can you find any 
relation between the xruns and system activity (disk access, incoming 
midi stream, GUI interaction, etc...) ?

Thomas




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