On Wed, 2004-09-29 at 20:49, Greg Reddin wrote:
This is something that has bugged me ever since I
built my Linux DAW.
When I boot up, when I start jack, when I open a web page with
Flash, when I get a licq message -- anything that uses my audio
driver, I hear a fairly loud low-end pop.
Is this common? Is it a known issue I can fix? I figure it's a
problem somewhere in the following (backwards) chain:
Delta1010LT hardware (SPDIF out) -> Delta1010 alsa driver -> alsa
library -> jack.
I cringed when I read this post. I had the same sort of problem when
I was attempting to use the RME HDSP 9652 under Linux. I was never
solved in my case and was enough for me to give up on Alsa ad Linux for
a good while. Since the HDSP line has such good support tools, hdspconf
and hdspmixer, I was able to trace a lot of stuff that you may not be
able to with your tools as I don't know what you have available.
In my case, which is not shown on your diagram, I was using an
external D/A, an Alesis AI-3. The free-running default frequency of that
unit is 48KHz. All of my work with Alsa (and Pro Tools) is at 44.1KHz.
Using hdspconf I could see that when these pops were happening the
frequency that the card was trying to work at was changing. As I'd load
an app, like Mozilla, the card's frequency would jump to strange values,
like 32KHz, and it was this frequency change that caused the pops, or so
I think. No other user of the HDSP 9652 seemed to report similar
problems so people would tell me that I had a defective card, but the
machien was dual boot and the frequency changes did not happen under
Windows and neither did the pops.
Eventually I gave up, moved the card to a different machine and
settled for running Linux using an AP2496. NIce card, but not an HDSP
I don't know if this info will help you get tot he bottom of your
problem. Most likely your cause is completely different but I thought
I'd bring the idea of your external equiment and it's interaction across
the s/pdif bus as a possible cause.