Weird IAC bus bug in 10.5?

Love 10.5 but have one small issue.

 

I sync LPX with Pro Tools (2020.5) using IAC bus on an iMac Pro (0S 10.14.6). I use PT for sync sound on film & tv projects and LPX for writing score cues.

 

In LPX 10.4 (and previous versions also) this worked perfectly. But in 10.5 when I switch desktops on the iMac to PT, then switch back to Logic, the sound drops out in PT for a second or so. It didn't do this in any previous version of LPX. Not the end of the world, but an irritating little glitch.

 

I've submitted a bug report to Apple, but does anyone have any thoughts as to why this might be happening in 10.5?

 

Thanks,

 

M

The sound drops out in PT? I'm not sure what this has to do with Logic - are you piping the audio output of PT back into Logic, or something?

 

Does the sound drop out in PT when switching desktops *without* Logic running?

 

How much RAM are you using?

Maybe it’s having issues sharing an audio device.

 

What happens if you put the same device for system audio and then open iTunes (or some system related audio app)?

Thanks for the replies. Don't have any issues generally with sharing audio devices. I used PT as main DAW until 2015 but since then have switched to using LPX as my main DAW and PT as a virtual tape deck (synced using IAC bus). I know it seems like this issue is to do with PT, but this only became a prob when I updated to LPX 10.5. I have both LPX 10.4 & 10.5 on my iMac Pro, and this only happens when I sync LPX 10.5 with PT. All was good in 10.4 (and indeed all previous versions of 10). It's a weird one, and I can't figure it out. PT version is unchanged. I thought it might be related to Live Loops, but happens regardless of using Live Loops or not. Not piping output of PT back into LPX. Both outputs going at the same time into my RME 802 interface. It's a relatively minor annoyance, but it's a bit distracting for me when sync sound in PT drops out briefly. Thanks, M.

Yes, I meant maybe logic 10.5 is having an issue with device sharing. So what happens in logic if you use the audio device for system and open iTunes or something else that uses system audio? As a test to rule out an issue specifically between logic and pro tools. Then try using protools while iTunes is running. This will show of either logic or protools has an issue with sharing and if it happens with both it may be a system issue.

Thanks for the input. I tried your suggestions but there don't seem to be any issues with system audio or either LPX or PT running with iTunes. Good idea to check that though. I think it's an IAC issue, but will run some tests today. Might row back my version of PT to also rule that out. Cheers, M.

IAC are part of macOS, not part of Logic. Did you update macOS when you updated Logic to 10.5?

Hi David, good point. Yes, I updated from High Sierra (10.13.6) to Mojave (10.14.6). But the strange thing is that the issue only occurs when I use LPX 10.5 with PT (2020.5) over IAC bus. When I use LPX 10.4 I have no problems...

That's odd, unless there's an issue with Logic Pro X 10.5 routing data to IAC busses of course but I can't imagine why there would be. Can you troubleshoot your IAC busses with a MIDI Monitor like Snoize's to see at what point the data breaks down?

Hi David, I will try your suggestion. Never heard of Snoize but will give it a go! On further investigation I can now see that the sound dropping out in PT - when synced over IAC bus with LPX 10.5 - is because MTC sync is lost briefly with PT when I switch back to LPX from PT. There's a drop out. But I can switch from LPX to PT without losing sync. So this has nothing to do with the sound engine. Thanks, M.

Hi David, I tried your suggestion and downloaded Snoize, which was a great idea. When I used it to monitor the IAC bus, I could see the MTC data flow stop momentarily - a fraction of a second - exactly at the point when I switched from PT back to LPX 10.5 when they were synced and running together. This was enough of a jump for the sound to drop out in PT for 1-2 seconds while it chased the sync again. When I tried this process using the same project template but in LPX 10.4 (synced to the same PT session), the data did not pause but was continuous and there was no issue with the sync or dropouts...

 

P.S. I should mention that all the midi sync prefs in LPX 10.4 & 10.5 are the same. No delays in MTC code or pickup delay.

Very interesting. So it would seem like 10.5 has an issue with you switching apps and that creates the hickup in MIDI transmission then perhaps? I would report this to Apple using their feedback form (link in the Bug report section at the top of this forum).

Yes. I can't see any other other explanation at this point. Thanks to your suggestion to use Snoize, I was able to confirm the interruption of MTC code. So thank you. I had already submitted a bug report but at that point I was unclear what the issue was. Now that I have more detail, I'll get back to them. Cheers David, M.

Great. You're welcome!