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Old 08-21-2018, 07:30 AM   #33
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Originally Posted by Jack Winter View Post
Great news. Since I have little experience with this, would you mind doing some short tests to see if everything aligns properly? Connecting a loopback cable and using reainsert will allow you to test what the actual real world latency is as opposed to the one calculated by buffer x period / samplerate (which is the only one reaper knows about). You can even add this to the recording prefs (or to the jack command line) to hopefully get it aligned down to the sample.
The reported latency on reainsert is 192 samples, but running the ping test comes back with 206. This was tested while letting QjackCtrl start jack up so that both cards were functioning, which did revert back to the 1.4/2.9ms, which is how it always read in Windows with the M-Audio ASIO drivers.

Another way to check the final result would be to insert a click source on one track and then play it back on output 1/2 and recording it onto input 1/3. I don't think this solution would introduce any extra latency between the 2 cards, but it would be nice to have that verified, and I suppose it would save you some work in the future not having to move tracks to line them up
The alignment issue isn't due to latency. It's due to the two cards not kicking into record at the exact same precise moment, so there is drift of the start time, but no drift otherwise. Sometimes they will be almost on the money with each other, and other times they will be off a bit from each other. I just did a test where I had all four inputs in record, and then sent them all the same mix of the single click of a pair of drumsticks. Here's what I got. The second card got into record a fraction later than the first card. If I scoot the second card's track to the left to match the first card, then all following events will be on the money with each other.

That looks good indeed. Did you have to add the threadirqs boot flag, or did it work without it? Something I'm not sure about concerning ubuntu's lowlatency kernel configuration.
I didn't have to do anything beyond installing rtirq with Synaptic, and then making the modifications you posted to it's config file.
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Last edited by Glennbo; 10-22-2018 at 04:14 PM.
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