Re: DirectSound and full-duplex

Tech-Archive recommends: Repair Windows Errors & Optimize Windows Performance

On Sun, 31 Jul 2005 21:59:19 -0400, "Chris P. [MVP]"
<msdn@xxxxxxxxxxxx> wrote:

<snip>
> If I
>knew enough about it's interfaces I would be tempted to write a low latency
>replacement.
I'd also be interested in doing this. Do you know if the information
is publicly available, in the DDK or something? It seems to me that
if the ADC and DAC operations begin at the same time, assuming
sample rates are the same, then the Nth ADC sample should
correspond to the Nth DAC sample, even if it takes a while to get
everything through all the FIFOs and kmixer buffers. The fact
that they don't is puzzling, and may imply that there is some
hardware issue that isn't being dealt with.

But if it was a constant sample offset for any given card, then
at least a user could calibrate to each particular card with a
loopback. At the moment, however, it seems we can't even
be sure that the ADC and DAC processes are getting
started by Windows at the same time. My informal experiments
show that just giving waveInStart followed by waveOutWrite
doesn't assure this, nor would we expect it... Windows could
always decide it needed to refresh the cache or something between
commands. I guess a custom driver would need to prevent
that by running in Ring 0 and shutting off interrupts, etc.

Ahhh, I guess this is what keeps us all from getting too
complacent!

Best regards,






Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator
.

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