You can find some common sound chip specs at the ALSA ftp site.
ftp://ftp.alsa-project.org/pub/manuals/
I once looked through the entire AC97 spec sheet trying to find a way to
get DC response for the ADC's but to no avail. I also hacked up a Creative
sb16(vibra chipset) by removing the input coupling capacitors and it
helped a little but still no DC response. Some of the pro quality
soundcards might work ok but they cost almost as much as a low end data
acquisition card. Oh well...
Chris|
On Fri, 26 May 2000, Peter Lindener wrote:
> Hi
>
> On the subject of sound cards and DC response ( bypassing the 20 Hz Hi pass
>filter caps )...
>
> I recently did my best to revers engineer the Creative Labs SBLive card to the
>point of figuring out what it would take to
> make it's analog I/O DC coupled. I was successful with the 4 Channels of SBLive
>analog output, but was some what
> more discouraged after looking into how the Analog inputs are digitized.
>
> Unfortunately the Creative Labs labeled AC 97 Intel spec component compatible
>Codec ( much like the Analog Devices AD1881 or Crystal CS4299 )
> used for A/D conversion seems to contain a Hi pass filter implementation that I am
>assuming is digitally implemented, as there are no associated
> external filter time constant capacitors. If any one has more info on this or would
>like to find out more info on this , possibly by talking to the folks at Creative
>Labs, please
> do so!. In any event, As thing stand, this Codec IC embedded Hi pass filter makes
>for problematic DC input measurement using the SBLive,
> even after bypassing the external AC input filter coupling capacitors.
>
> As for the 50 / 60 line noise problems mentioned by some, this is sounding like
>it may be related to ground loop current problems.
> Best to use differential structures that provide ground references that do not have
>potential currents that could flow also in them.
>
> So in summery the SBLivescan easily be made to do DC coupled Analog output.
>Although these out are implemented by means of
> sharp cutoff Delta-sigma D/A converters with there associated typically 833 uSec. @
>48Khz. Fs. (40 samples ) of digital interpolation filter group delay.
>
> Cheers
> -Peter (650) 694-7352
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