Full Version: AC97 Automatically Resamples to 48K?
Trying to hunt down an odd distortion on a neighbor's rig. Can someone tell me definitively if AC97 chipsets always resample 44.1k output to 48k in hardware? If so, is there a way to disable this? Or alternatively, if I feed it a 48k output (via software resampling) will it leave it unmolested or will it resample it again like those crappy LiveBlaster cards once did? Many thanks in advance.
QUOTE(ears @ Aug 18 2005, 12:02 PM)
Trying to hunt down an odd distortion on a neighbor's rig. Can someone tell me definitively if AC97 chipsets always resample 44.1k output to 48k in hardware? If so, is there a way to disable this? Or alternatively, if I feed it a 48k output (via software resampling) will it leave it unmolested or will it resample it again like those crappy LiveBlaster cards once did? Many thanks in advance.
Use ASIO audio drivers.
Asio4all
Asio driver specific to your media player.
Kevin
Asio4all doesn't help much because it reverts to kernel streaming or direct sound.
1. you can use udial (search the forums) to check if the soundcard resamples.
just be careful with the volume, as this file has blown many-a-tweeter
similarly, it can be used to check if resampling to 48 kHz in software resolves the problem
2. afaik, all ac97 codecs resample by design
3. afaik, 48 kHz signal isn't re-processed
4. those things don't support ASIO natively, and using asio4all would be just emulating it through kernel streaming.
not exactly smart™, if you're asking me - you might as well switch to the kernel streaming output component in foobar2000
just be careful with the volume, as this file has blown many-a-tweeter
similarly, it can be used to check if resampling to 48 kHz in software resolves the problem
2. afaik, all ac97 codecs resample by design
3. afaik, 48 kHz signal isn't re-processed
4. those things don't support ASIO natively, and using asio4all would be just emulating it through kernel streaming.
not exactly smart™, if you're asking me - you might as well switch to the kernel streaming output component in foobar2000
Interesting, something further to look into. My understanding is that some AC97 codecs do support 44.1kHz operation, I have my external dac connected via spdif to a Realtek RLC650 which the manufacturer claims does support this.
It's anyone's guess as to what is actually coming down that spdif line, my dac supports 48kHz but does not indicate the sample rate. WinAmp and Foo both report 44.1kHz but obviously this does not mean it is 44.1kHz at the output.
Kevin
It's anyone's guess as to what is actually coming down that spdif line, my dac supports 48kHz but does not indicate the sample rate. WinAmp and Foo both report 44.1kHz but obviously this does not mean it is 44.1kHz at the output.
Kevin
QUOTE(Moneo @ Aug 18 2005, 02:50 PM)
1. you can use udial (search the forums) to check if the soundcard resamples.
just be careful with the volume, as this file has blown many-a-tweeter
similarly, it can be used to check if resampling to 48 kHz in software resolves the problem
2. afaik, all ac97 codecs resample by design
3. afaik, 48 kHz signal isn't re-processed
4. those things don't support ASIO natively, and using asio4all would be just emulating it through kernel streaming.
not exactly smart™, if you're asking me - you might as well switch to the kernel streaming output component in foobar2000
just be careful with the volume, as this file has blown many-a-tweeter
similarly, it can be used to check if resampling to 48 kHz in software resolves the problem
2. afaik, all ac97 codecs resample by design
3. afaik, 48 kHz signal isn't re-processed
4. those things don't support ASIO natively, and using asio4all would be just emulating it through kernel streaming.
not exactly smart™, if you're asking me - you might as well switch to the kernel streaming output component in foobar2000
i'm using an ALC658 onboard chip at the moment and i don't know why, but when i use the realtek drivers, the udial test fails and when i use the via drivers, the udial test passes.
-andy-
-andy-
AC'97 was 48khz-only initially, 44.1 was added in later revisions of the spec.
QUOTE(HbG @ Aug 19 2005, 08:56 PM)
AC'97 was 48khz-only initially, 44.1 was added in later revisions of the spec.
My asus mobo has the Realtek ALC650 AC97 codec and so far I have not been successful in defeating the resampling to 48kHz - and I can at least confirm that this seems to be the default for this chip and presumably for all (?) AC97 codecs. What I am trying to figure out is this purely a hardware constraint or is it dictated by driver design??
Nvidia provides Gforce drivers for this mobo, which in this case includes the audio driver support. Nvidia provides an asio driver as part of the package, but it does not seem to prevent resampling. (Nvasio.dll - Nvidia Asio)
I also tried the actual Realtek drivers I downloaded today and these do not apparently even provide asio support.
The sound quality through the spdif is not bad after extensive tinkering, but the inability to play back HDCD encoded material in HDCD is a definite bummer and apparently is due to the resampling. (I tried my m-audio transit with my external dac via optical spdif and that successfully played back HDCD.. The dac recognized the HDCD encoding, overall however I was not pleased with the results.)
Anyone have any suggestions? Should I just buy a sound card as I originally planned?
Thanks, Kevin
Don't expect miracles from onboard sound. 
That's a yes in case you were wondering. Don't buy Creative if you need native 44.1 though.
That's a yes in case you were wondering. Don't buy Creative if you need native 44.1 though.
I was thinking along the lines of the EMU0404 or M-Audio 2496. Possibly RME..
All I really need is a stereo card with coaxial spdif and native 44.1kHz support..
Just wanted to make sure I wasn't missing something obvious, nvidia asio chipset support for this device must be mainly for low latency applications? The nvidia mixer controls are always active even if the application controls are not..
Kevin
All I really need is a stereo card with coaxial spdif and native 44.1kHz support..
Just wanted to make sure I wasn't missing something obvious, nvidia asio chipset support for this device must be mainly for low latency applications? The nvidia mixer controls are always active even if the application controls are not..
Kevin
QUOTE(HbG @ Aug 21 2005, 07:13 PM)
Don't expect miracles from onboard sound.
That's a yes in case you were wondering. Don't buy Creative if you need native 44.1 though.
That's a yes in case you were wondering. Don't buy Creative if you need native 44.1 though.
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