jack with multiple cards?

[tjb]

Hey guys,

so I am changing my status from a lurker to a writer ... now. I just purchased a Behringer UFX1204 because I read good things about it in here, and it works just fine. But I don't want to retire my Scarlett 2i4, so it is somehow possible to use both interfaces simultaneously? atm I have the input set to the UFX and all output goes to the Scarlett, but this will break if I reboot and the mixer is off. It would be cool if I somehow could merge these two and don't have care anymore about if one device is on or not. I've read this and am just about to try alsa_in/alsa_out. Anybody tried this? Any tips?

cheers

[tjb]

well this works better than I expected. I now just start the Scarlett at login and afterwards an "alsa_in -j UFX -d hw:UFX1204 -c 16 2>&1 1> /dev/null &" and everything runs juicy. also, no xruns anymore (there were some before as the input was the UFX and the output was the scarlett, I suppose)! wow. let's see how this setup performs in a real recording session though ...

[tjb]

ok, for anyone interested: after a night of testing here is the final solution which works ok for me with this setup. I found alsa_in to be a bad cpu hog so I switched to jack2 audioadapters. cpu spikes gone, and after only hours of fiddling (argh) with the sample rate settings no Xruns anymore, and after another hour fiddling (aaargh) with the recording offset in Bitwig a okayish compensation, so no record delay. jack starts with the scarlett only, and when I want to record, I load an UFX adapter with

Code: Select all

 jack_load -i "-d hw:UFX1204 -i16 -o4"  

whew! perhaps this helps someone else.

[aicram]

Wow! Great this worked out so well.

Very useful information.

Thank you.

aicram

[tjb]

"worked out so well" is relative ... *sigh* - after some live jamming/recording I noticed that jack_load introduced some weird noises into the audiostream so all the recordings went to shit. sounded like a broken phone ringing. damn this shit sucks.

I am now back to square one: use jack with different input and output devices. I had to turn up the latency (512/4@96000 = 10.7) to get rid of the dropouts (which occasionally *still* happen) and introduce some extra frames measured with jack_iodelay to get the recordings tight enough.

all this now works but it still sucks. damn you linux audio. next option: merge the cards with alsa into a pseudo device. anybody did that before?

[sadko4u]

Did you try this?

http://www.penguinproducer.com/Blog/201 ... with-jack/

[tjb]

yes, see second post. too much overhead.

[sadko4u]

yes, see second post. too much overhead.

What buffer size do you use in JACK configuration?

[tjb]

current settings, which work really good: jack input device: UFX1204, jack output device: scarlet 2i4, buffer size: 256, periods: 4, samplerate: 96k, extra latency (in&out): 200, bitwig recording offset: -1024. this is now as tight as it gets, but not totally perfect (in terms of beat to grid recording).

another gambling with the settings got me the result that the midi clock (sent from bitwig) is unstable and jumps around +/- 0.20 bpm. so probably *this* is the "not tight enough" issue. no idea how to fix that though. I tried lowering the audio buffer sizes with no success. I also tried sending clock from sequencer64 but it is the same jumping here, so that seems not to be a bitwig issue.

edit: forgot samplerate.