Audio clock generation

Hi all,

First of all, I want to say that my setup is running pretty well.

I'm using a Virus TI connected to my computer through USB and spdif.
I have two PCI soundcards. The first one is an onboard one ; I'm not using it for making music.
I do not use the VirusControl plugin, I use spdif to transmit the audio to the input of my second soundcard.

My second soundcard is an Audiophile 2496, which for some reason (found in the user's manual), must be configured as spdif clock slave (otherwise, no spdif audio is received on the card's input).

If I go to "Audio Clock" config menu on the Virus TI LCD, I see "Frequency : Synced to Host".

This setup works fairly well in most cases ; But, sometimes, I can hear pops & crackles which I can't get rid of, except by a complete reboot (reset computer + unplug synth power cord + edit-arp-power-on).

My questions are :
1/ Who is generating the audio clock in these situations?
2/ What is my Virus TI sync'ed to? My second soundcard? How do the TI knows that it is spdif-connected to this soundcard?
3/ Is the Virus TI USB audio driver generating a clock from software?

Thank you for your answers!

In fact, I'm experiencing trouble with my setup. I'm running Windows XP.
Sometimes, the soundcard gets stuck, when opening the audio device. I cannot play any sound, players start playing but are stuck on "0:00" and I hear nothing.
If I switch the clock of my soundcard to "internal" (instead of spdif) then I can play sounds again. If I switch back to "spdif" immediately, the soundcard is still stuck. But If I play a song (clock being set to "internal") for some time, then set the clock back to "spdif", the soundcard is working again.
When my Virus was only connected by MIDI+spdif, I didn't have this problem. I'm having this trouble only since I'm connecting the Virus TI using USB (I only use USB for MIDI, all audio goes through spdif). So I'm suspecting the Virus not to correctly generate spdif clock in this case.
BTW it never gets stuck in the middle of a song. It's always at the beginning (when the application opens the device).
That's why the audio clock generation is so important : i'm afraid there's some kind of clock loop here (virus clocked by usb driver, usb driver clocked by soundcard, soundcard clocked by spdif, spdif clocked by virus ???).
If somebody with enough technical knowledge to understand what's going in my setup would answer to my questions, I'd be very gratefull!

Another information : If I boot under Linux, same connections (spdif + usb), I'm never having this problem. It only happens under Windows XP. Of course, under Linux, the soundcard driver is different, and the drivers for the virus are different (I wrote one part of them actually ).

Hi InSub,

Do you also experience audio getting "stuck" ?
I found a workaround, which is to always let, in the background, a media player (vlc, foobar, winamp) on pause (not stop)

Cheers.