[LAU] irq sharing

Niels Mayer nielsmayer at gmail.com
Tue Aug 24 19:46:06 UTC 2010

On Tue, Aug 24, 2010 at 8:13 AM, David Santamauro <
david.santamauro at gmail.com> wrote:

> thanks for the time. I only have one PCI slot, but 3 empty PCI-x slots.
> I basically unplugged all USB devices as well as shut off both network
> interfaces and on board audio interface in the bios and the noise
> persists ...
> Not sure what to try next, this was a shot-in-the-dark.

If you think it's a interrupt-sharing issue, consider using a pcie-to-pci
riser to plug in your card. Apparently, this way of doing things may ensure
less bus contention:

Also, be sure that interrupt contention is really the problem. If it's a
constant noise, there's a better chance that it's a different problem. One
issue is that your recording software may not be using the same bit depth,
alignment, or complement as what the card expects. I can get this effect on
output, for example, simply by using 'mplayer'

$ mplayer -quiet http://media.kcrw.com/live/kcrwlive.pls -ao
Opening audio decoder: [mp3lib] MPEG layer-2, layer-3
AUDIO: 44100 Hz, 2 ch, s16le, 112.0 kbit/7.94% (ratio: 14000->176400)
Selected audio codec: [mp3] afm: mp3lib (mp3lib MPEG layer-2, layer-3)
AO: [alsa] 44100Hz 2ch s16le (2 bytes per sample)
Video: no video
Starting playback...

IMHO, the problem w/ mplayer is the fact that it passes on the "s16le"
format of the stream straight to the soundcard. This results in something
that sounds like the original signal, but superimposed with all sorts of
garbage and noise.

Playing the exact same stream using
$ gst123 -a alsa=66ch34
uses the correct format and so the playback sounds as intended.

I'm thinking that something similar w/r/t bit order/depth/complement/etc
might be happening on record/capture from your 1010?

What happens when you setup jackd to talk to your soundcard? My experience
is that Jackd seems to do the right thing w/r/t matching the bit
order/depth/complement expected by the soundcard.

-- Niels

PS: If this doesn't help, perhaps asking on the alsa-dev list may help?
Alternately, perhaps someone from the ALSA project (Clemens Ladisch?)  may
know about this problem and how to resolve it.
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