Card won't accept new sample rate?

Card won't accept new sample rate?

[Daniel James]

Hello all,

Here's a strange problem that's affecting at least three different 
machines running Debian, or in our case, the 64 Studio distro made up of 
Debian packages:

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=377915

This bug is not related to qjackctl, as first thought. Here are the 
steps to reproduce it:

1. Start jack on the command line at 44100Hz using the alsa backend

2. Start any jack application and see the sample rate reported as 48000Hz

In fact it doesn't matter which rate you try to start jack at, the 
sample rate is always reported as 48000Hz. This bug only happens with 
the alsa backend, the oss and dummy backends work as normal.

The problem has been observed on three different AC97 soundcards, 
running various kernels from 2.6.16 to 2.6.17. The alsa-base version is 
1.0.11-5. However one machine with an AC97 on-board sound chipset, 
running Debian unstable, does not show the problem. Also, all these 
machines were working fine with ALSA and jack until recently.

Any clues would be greatly appreciated. A machine is available on-line 
for testing if that is required - if you would like to log in to it, 
please let me know and I'll send you the IP address and login.

Cheers!

Daniel

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Re: Card won't accept new sample rate?

[Takashi Iwai]

At Tue, 29 Aug 2006 14:19:41 +0100,
Daniel James wrote:
> 
> Hello all,
> 
> Here's a strange problem that's affecting at least three different 
> machines running Debian, or in our case, the 64 Studio distro made up of 
> Debian packages:
> 
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=377915
> 
> This bug is not related to qjackctl, as first thought. Here are the 
> steps to reproduce it:
> 
> 1. Start jack on the command line at 44100Hz using the alsa backend
> 
> 2. Start any jack application and see the sample rate reported as 48000Hz
> 
> In fact it doesn't matter which rate you try to start jack at, the 
> sample rate is always reported as 48000Hz. This bug only happens with 
> the alsa backend, the oss and dummy backends work as normal.

OSS does software sample rate conversion as default.

> The problem has been observed on three different AC97 soundcards, 
> running various kernels from 2.6.16 to 2.6.17. The alsa-base version is 
> 1.0.11-5. However one machine with an AC97 on-board sound chipset, 
> running Debian unstable, does not show the problem. Also, all these 
> machines were working fine with ALSA and jack until recently.
> 
> Any clues would be greatly appreciated. A machine is available on-line 
> for testing if that is required - if you would like to log in to it, 
> please let me know and I'll send you the IP address and login.

My wild guess is that your ac97 codec chip really supports only
48kHz.  For example, C-Media codecs do so.

Check your /proc/asound/card0/codec97#0/ac97#0-0 file, whether it
contains "VRA" in Extended ID section.  If not, it's 48k-only codec.


Takashi

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Re: Card won't accept new sample rate?

[Daniel James]

Hi Takashi,

> OSS does software sample rate conversion as default.

Right, that figures.

> Check your /proc/asound/card0/codec97#0/ac97#0-0 file, whether it
> contains "VRA" in Extended ID section.  If not, it's 48k-only codec.

Indeed it does not - thanks for the clue :-)

I have put an extra soundcard in one of the test machines showing the 
problem. The new card has the ice1712 chipset, and this changes sample 
rate perfectly.

Is there any change that has been made to ALSA recently, which would 
mean that a 48k-only chipset no longer does sample rate conversion in 
software by default? If not, could this be something broken in Debian's 
configuration of ALSA?

Thanks!

Daniel



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Re: Card won't accept new sample rate?

[Takashi Iwai]

At Tue, 29 Aug 2006 15:32:10 +0100,
Daniel James wrote:
> 
> Hi Takashi,
> 
> > OSS does software sample rate conversion as default.
> 
> Right, that figures.
> 
> > Check your /proc/asound/card0/codec97#0/ac97#0-0 file, whether it
> > contains "VRA" in Extended ID section.  If not, it's 48k-only codec.
> 
> Indeed it does not - thanks for the clue :-)
> 
> I have put an extra soundcard in one of the test machines showing the 
> problem. The new card has the ice1712 chipset, and this changes sample 
> rate perfectly.
> 
> Is there any change that has been made to ALSA recently, which would 
> mean that a 48k-only chipset no longer does sample rate conversion in 
> software by default? If not, could this be something broken in Debian's 
> configuration of ALSA?

If you start JACK, usually it prefers "hw" PCM, which means the direct
access to the hardware without resampling, up/downmix, and format
conversion (also without soft-mixing).  The "default" PCM is with
everything, i.e. dmix, and plug layer.

So, I guess this is intentional behavior.


Takashi

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Re: Card won't accept new sample rate?

[Daniel James]

Hi Takashi,

> If you start JACK, usually it prefers "hw" PCM, which means the direct
> access to the hardware without resampling, up/downmix, and format
> conversion (also without soft-mixing).  The "default" PCM is with
> everything, i.e. dmix, and plug layer.

Right - I just tried 'default' on my laptop, which points to the AC97 
chipset, and JACK wouldn't even start at 44100Hz. I switched to 
'default' at 48000Hz and it worked.

However if I plug in a USB audio interface (M Audio MobilePre), used as 
hw:2, then jack starts fine at either 44100 or 48000 and the sample rate 
is correctly displayed in qjackctl.

I think it's because of this USB interface that I believed JACK used to 
work at 44100Hz on this particular laptop. Now I know different :-)

Thanks!

Daniel


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