[AG-TECH] Current soundcards in use with Alsa and rat?

Robert Olson olson at mcs.anl.gov
Thu Dec 23 09:47:27 CST 2004

This effect can be explained if you look at the architecture of AC97 
sound chip.

Below (if you can see HTML mail, if not, the image is from the 
datasheet at


you will see the block diagram of a typical AC97 device. Note that all 
inputs route through a selector, then to what this datasheet calls a 
PGA, a programmable gain amplifier. The gain on that amplifier is what 
controls the input capture level. This level adjustment is exposed in 
the OSS audio drivers as the Igain or Reclevel control, I believe. I 
don't recall what ALSA calls it. Adjusting the line-in volume level 
controls the gain in the line-in -> output mixer -> line out signal 
path, which is why that level must be set to zero to keep local 
loopback from occuring.

The OSS code in rat attempts to detect if the soundcard in use is AC97 
compatible (currently, by using a hardcoded list of device names). If 
it determines that it is AC97, it maps the capture volume control to 
control the igain signal and sets the line in level to zero, making rat 
act correctly.

I haven't looked closely at the ALSA rat code, but I suspect that it 
needs to have similar changes made.


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On Dec 22, 2004, at 5:34 PM, Eric Olson wrote:

> Thanks Rhys, that does help some.  With our intel card, setting the
> line-in volume to 0 on rat does keep me from hearing my own voice, too.
> Moving the capture volume meter didn't seem to have any effect on the
> sending volume (although the capture switch in amixer does turn capture
> off or on), so we don't have a way to control that volume yet, but 
> it's an
> improvement.
> Eric
> On Thu, 23 Dec 2004, Rhys Hawkins wrote:
>> Hi Eric,
>> I'm using just the onboard soundcard with rat/alsa and its working
>> fine. Its an Intel 82801DB-ICH4 (thats what rat reports). I'm using
>> Steve Smith's version of rat, as the one that ships with the gentoo
>> version of the AGtk had issues using the alsa driver.
>> The only other thing is that the mixer settings are difficult to
>> work out. For example, I had to set the microphone volume to 0
>> and capture to 50 to be able to talk and not hear my voice played
>> back to me which to me seemed counter-intuitive. I guess whats
>> missing is some documentation explaining what each of the mixer
>> settings actually do.
>> I've also got a Soundblaster Audigy going, but I actually prefer
>> to use the onboard card as it works and the mixer settings are
>> much simpler by comparison.
>> Cheers,
>>     Rhys
>> On Wed, 2004-12-22 at 15:46 -0600, Eric Olson wrote:
>>> Hi,
>>> For those of you on linux using Alsa with rat, can you tell me which 
>>> sound
>>> cards you're using successfully recently?
>>> I've had problems with a couple cards so far, and would like to try 
>>> one
>>> that someone else is using, preferably with the Alsa driver instead 
>>> of
>>> the OSS compatibility driver, but anything that works (without the 
>>> line-in
>>> playback issues) would be great.  Someone mentioned that the Sound 
>>> blaster
>>> live should work -- are there any others I can try before buying one 
>>> of
>>> those to try it?
>>> Here are my experiences so far with two cards:
>>> es1370 for the sound blaster pci 128 (model CT4700):
>>>   alsa driver fails on an assertion when running.
>>>       rat-4.2.22-media: simple.c:1412: 
>>> snd_mixer_selem_has_playback_volume:
>>>       Assertion `elem' failed.
>>>   OSS driver plays correctly but rat often resets the line-input 
>>> playback
>>>       to on (i.e. when the volume is changed)
>>> intel8x0 integrated audio:
>>>   alsa driver sounds mechanical and seems to be playing back a 
>>> little too
>>>     slowly.
>>>   oss driver has the same line-input playback problem as the other 
>>> card.
>>> I'm testing with rat from both Doug's and Steve's recent packages 
>>> and the
>>> results are the same.  I've also built rat from UCL's cvs, but rat 
>>> only
>>> sees the OSS device and not the Alsa device, so I'm probably missing
>>> something when building.
>>> I wouldn't mind helping fix some of these issues, but in the 
>>> meantime I
>>> hope to find an already working soundcard for our production node so 
>>> we
>>> don't have to keep running a script to fix the line-input playback
>>> setting.
>>> Thanks for any help,
>>> Eric

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