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Strange distortion

Hello,

I have a strange problem with distortion on even numbered outputs. It's only happening with strong transient sounds such as snaredrums. I'm running Logic Pro X 10.3.1 on a 2 x 2,26 GHz Quad-Core Intel Xeon Mac pro from 2009 (OSX 10.11.6) through a UAD Apollo 16.

I'm aware that it might be an issue with my soundcard, but since I've been in contact with UAD and they can't find a solution, I'm posting this here now in case anybody knows about this...

What happens is that I get this distorting sound as if the sound is breaking up on even outputs from the Apollo. It's not related to any hardware (patchbay, cables, mixing desk etc). And here's when it gets really strange: it only happens on even mono tracks - 2, 4, 6 and so on. So if I have a snare drum routed to output 1&2, it's all clean. Same thing if I route the snare to 1 (mono out). But as soon as I route it to 2 (mono out) it gets distorted. The same applies to any stereo bus, such as 3-4, 5-6 etc etc.

It's also not consistent - the problem comes and goes but most of the time it's there. The sounds I'm routing are not distorting in my DAW and I have plenty of headroom. Also, the CPU is not busy at all.

Then there's another thing that might or might not be a clue as to what is going on: as you can see on the screenshot, I routed a snare (topmost channel) through Apollo out, then back in to the Apollo via the patchbay. The two regions in the middle are the re-recorded snare through first output 1&2, then output 1 (mono). The one at the bottom is the snare re-recorded through output 2.

Now, as you can see, the first two re-recorded snares are significantly later compared to the original snare, whereas than the

last one (that was routed through line 2) starts at the same point but is chopped up/distorted (which can be seen on the waveform).

The fact that the first ones are later isn't that strange; I'm using my mixdown settings with high buffer size (Pic 2) so I'd expect the returning audio to be late and it's all in sync when I play back the whole project. But how come the audio going through line 2 is in sync with the original (and distorted)?

I have found a way to work around it by routing the snare (for example) to virtual channel 3 on the Apollo (or any uneven number of the available virtual channels, since the same problem occurs on the even numbers of the virtual channels as well) and then route the virtual channel to output 2 (or wherever I want it on my mixing desk), but it's not ideal.

Kind regards,
Ruben E

最後更新：2017-09-08 15:41:54

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