A friend and I have been jamming on some ideas for the last couple of weeks. Since I am stuck here on call today, I thought it might be a good time to delve a little deeper into Ardour.
My GNX2 has S/PDIF digital output, and my AMD64 box has an S/PDIF header, but the documentation is unclear, it appears that it is supposed to be output but then the manual also says it does I/O. I have no idea what would happen to either piece of equipment if I connected them and they were both running as output. From what I have read, it sounds like you could ruin something. Hmm, no thanks... What to do? Easy. Install the RME HDSP9652 back into the PC and let the digital recording commence!
I actually installed it last night, and this morning my first tests were under Windows 2000. The 9652 doesn't have analog out so I needed to use the SoundBlaster PCI512 (an older SoundBlaster audio card) that was already in my box for monitoring/playback. How did it go? Well, lets just say it didn't work out. The latency was so bad between the digital input to the analog output there was no way to do anything remotely useful. Hit a chord and wait two seconds for it to sound from the speakers. It was obviously on to Linux where I knew I would have to turn from the start...
DeMuDi was really my only option. I tried Musix but gave up trying to get ALSA to play with both sound cards at once. In DeMuDi, I was able to add the 9652 to the sound file under /etc/modprobe.d and from there it was just a matter of setting the sound levels on the GNX2, ALSA, and the HDSP mixer. Oh, and setting up the Ardour session and Jack connections. Whew!
All was going well, and I was happily recording some guitar parts when every once in a while it would sound like some terrible interference was cutting in. What was it? Bad connections? RF interference from something in the PC or around it? The soundblaster card freaking out? What?
That's when I started watching the xruns in Jack. Sure enough, I would hear that noise and see the xrun counter increment. Latency issues. :-(
I tried tweaking the Jack settings and it got better but didn't clear up entirely. I continued with my recording but thought for sure that the noise was going to make a mess of the whole experiment. It's funny, I've never heard this noise with the softsynths when I got an xrun, nor any issues with recording through the soundblaster as far as I can recall. The RME card does all it's own processing and doesn't hit the PC CPU at all. Oh well... I continued on...
When I exported my hastily pieced together Ardour session to a WAV file, I discovered something interesting. Upon playing it back the xrun noise was gone. Not a trace. It was only during playback & monitoring during the recording that I heard it. Now it was gone and I was left with a pristine recording (too bad my rhythm was so awful on the piece). (Otherwise it was) Excellent!
It must be an issue with the soundblaster and/or jack settings. After all, it appeared that there was nothing wrong whatsoever with the digital input signal and the RME card uses zero percent of the PC processor. The answer must lie there somewhere...
Oh goody, more research to do on arcane computer topics. Just what I love! ;-)