Problem with snd_ich and vchans

Thomas E. Zander riggs at
Wed Dec 10 14:34:46 PST 2003


On Wed, 10. Dec 2003, at 22:20 +0100, Michael Nottebrock wrote
according to [Problem with snd_ich and vchans]:

> Now when I enable vchans, sound plays back to slowly (pitched down), fiddling 
> with above sysctl doesn't have any effect. I found the following in vchan.c:
> [...]
> When I change the 44100 to 48000 there, sound plays back normally with vchans 
> enabled.

I think vchans and AC97 is an ugly trap. The main problem is the crappy
definition of the AC97 standard. It's intended to run on 48kHz only
which forces software resampling for many sources. Because of this some
vendors produce codecs which run internally on 44.1kHz and try to
resample any incoming source, and some don't.
Thus, it would be necessary to have a table for every AC97 codec to
determine which is its default base frequency in order to set it
For example, the AC97 codec on my mobo does this default resampling to
44.1kHz, so if you have vchans enabled and you want to play a 48kHz
source like DVD it sounds like framedroppings. Luckily, mplayer can
resample :-)

Yes, it's time to create a *good* successor of the AC97 standard, but
until it arrives, we have to live with some unfortunate cheats.


- "[...] I talked to the computer at great length and
-- explained my view of the Universe to it" said Marvin.
--- And what happened?" pressed Ford.
---- "It committed suicide." said Marvin.
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