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
Nicolas FERRE wrote:
> Thomas Gross wrote:
>
> > i need the ADC of the sound card for data aquisition for 2 channels with
> > sampling frequency of 44.100 Hz. I read the data into the buffer and then i
> > want to calculate fft and some other functions. Are there some drivers
> > available?
>
> I work with a Sound Blaster PCI128 (es1371 (=1373) chip) and I plan to
> port the driver to RTLinux... I will use David Olofson 's DPI ( Driver
> Programming Interface layer). You can download the DPI 0.1.0 (beta) -
> includes ES1370 (AudioPCI) driver ). I will use it as an example...
>
> http://www.angelfire.com/or/audiality/
> http://www.rtlinux.org/rtlinux/
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