Request for advice on stopping xruns

Request for advice on stopping xruns

[Fergus Reid]

Hi, I'm developing an 8 channel recorder based on alsa0.9.0beta10 and a
Terratec EWS88mt sound card.
I'm now using a 2.4.18 kernel with the Andrew Morton patches applied. I
really want to be able to record/playback at the full 96k 24bits on all
8 channels simultaneously, but I need absolutely no under/overruns.
Currently, as I try to up the bandwidth requirements I get xruns
occurring more and more frequently; I'm not even sure if I can guarantee

a maximum, before the onset of xruns, although 16bit 44.1 may well be
okay.

I don't care about other system processes, so I've set the record and
playback threads to SCHED_FIFO prio 99 (although I don't really know if
this is the right thing to do!)

Is there anything I can do/change/not do to eliminate xruns altogether?

Thanks,
Fergus





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Re: Request for advice on stopping xruns

[Paul Davis]

>Hi, I'm developing an 8 channel recorder based on alsa0.9.0beta10 and a
>Terratec EWS88mt sound card.
>I'm now using a 2.4.18 kernel with the Andrew Morton patches applied. I
>really want to be able to record/playback at the full 96k 24bits on all
>8 channels simultaneously, but I need absolutely no under/overruns.
>Currently, as I try to up the bandwidth requirements I get xruns
>occurring more and more frequently; I'm not even sure if I can guarantee
>a maximum, before the onset of xruns, although 16bit 44.1 may well be
>okay.
>
>I don't care about other system processes, so I've set the record and
>playback threads to SCHED_FIFO prio 99 (although I don't really know if
>this is the right thing to do!)
>
>Is there anything I can do/change/not do to eliminate xruns altogether?

You cannot eliminate xruns altogether. xruns are caused either by OS
scheduling delay, or by processor load. I trust that you are not
trying to read/write from/to disk from the same thread as you are
handling audio in ...

Ardour (http://ardour.sf.net) records 24 channels with 32 bit samples
with no xruns. Perhaps you are not familiar with this project. It uses
JACK (http://jackit.sf.net) as its underlying audio engine, which in
turn uses ALSA.

--p

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Re: Request for advice on stopping xruns

[Fergus Reid]

Paul Davis wrote:

> >Hi, I'm developing an 8 channel recorder based on alsa0.9.0beta10 and a
> >Terratec EWS88mt sound card.
> >I'm now using a 2.4.18 kernel with the Andrew Morton patches applied. I
> >really want to be able to record/playback at the full 96k 24bits on all
> >8 channels simultaneously, but I need absolutely no under/overruns.
> >Currently, as I try to up the bandwidth requirements I get xruns
> >occurring more and more frequently; I'm not even sure if I can guarantee
> >a maximum, before the onset of xruns, although 16bit 44.1 may well be
> >okay.
> >
> >I don't care about other system processes, so I've set the record and
> >playback threads to SCHED_FIFO prio 99 (although I don't really know if
> >this is the right thing to do!)
> >
> >Is there anything I can do/change/not do to eliminate xruns altogether?
>
> You cannot eliminate xruns altogether. xruns are caused either by OS
> scheduling delay, or by processor load. I trust that you are not
> trying to read/write from/to disk from the same thread as you are
> handling audio in ...
>
> Ardour (http://ardour.sf.net) records 24 channels with 32 bit samples
> with no xruns. Perhaps you are not familiar with this project. It uses
> JACK (http://jackit.sf.net) as its underlying audio engine, which in
> turn uses ALSA.
>
> --p

Er, actually I am doing it all in a single thread, I guess this is not a
good idea. I will
modify things and see how I go!

I looked at Ardour at the beginning of last year, and thought it looked very
good,
although I must confess I never got it to record. The JACK part doesn't ring
any
bells, I will take a look.

The reason I'm writing my own, far simpler, 8 track recorder, is because I
wanted
to do it for myself, being an ex Sound Engineer turned Computer programmer.
I did
look at the code for Ardour, but it was quite involved, and I didn't have
the time then
to get to grips with it. I actually ended up looking at how aplay works,
which is how
I've ended up with a single thread!!

Thanks,
Fergus






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