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  #1  
Old 08-04-2022, 02:45 PM
krocksf krocksf is offline
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Default Changing outputs during playback causes digital noise on input channels

I'm seeing a strange issue on my M1 MacBook Air running Pro Tools 2022.07 on macOS 12.4 (Monterey). I use an external summing mixer in my set up...and I've see this happen with both an Apollo x16 and an Apogee Symphony MKII 32x32. I create an Aux track with input channels 3 and 4 assigned to the interface so that I can monitor the mix coming back into Pro Tools. I then started playback and while playback was happening I assigned one of the audio tracks out channels 1 and 2 of the interface into my mixer. I did this a couple more times on a couple other tracks and eventually I got some nasty noise coming into the Aux track that was taking the input from interface channels 3 and 4. It's like a digital noise (like a super small buffer repeating super fast).

The noise persists, even when playback is stopped. You can switch the input of the Aux track to channels 1 and 2 and the problem will go away, however as soon as you switch back to channels 3 and 4, it will come back. The only way to get it to stop is to either relaunch Pro Tools or toggle the sample rate on the interface to something else, and then back to what it was previously set to (in my case from 44.1 to 48 and then back to 44.1).

And weirdly enough, I've only seen this happen on inputs 3 and 4 at the moment. I haven't gotten it to happen if I start with input channel 1 and 2.

The noise is pretty nasty, so it's pretty annoying when it happens, and definitely interrupts your workflow. Anyone else seeing this?
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  #2  
Old 08-04-2022, 04:01 PM
peapodpost peapodpost is offline
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Default Re: Changing outputs during playback causes digital noise on input channels

maybe something(s) are having a hard time switching sample rates when you don't want them to?

can you hard-assign the same sample rate to all your gear?

use a buffer audio driver such as loopback, blackhole, omnibus, etc?
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Old 08-04-2022, 04:08 PM
Darryl Ramm Darryl Ramm is online now
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Default Re: Changing outputs during playback causes digital noise on input channels

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Originally Posted by peapodpost View Post
maybe something(s) are having a hard time switching sample rates when you don't want them to?
??? Nothing here will be switching sample rates, it's the same interface, it runs at one sample rate. (until manually changes to solve this problem).
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Old 08-04-2022, 04:30 PM
krocksf krocksf is offline
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Default Re: Changing outputs during playback causes digital noise on input channels

Exactly. My interface is set to 44.1, which is what the session is set to as well. All input/output changes are made in the same sample rate. When this problem occurs, I have to go behind Pro Tool's back to toggle the sample rate to fix the issue (using either Apollo Console or Apogee Symphony Control). Pro Tools will post a dialog about there being a sample mismatch, but after you dismiss that, things are back to normal.
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Old 08-04-2022, 04:32 PM
krocksf krocksf is offline
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Default Re: Changing outputs during playback causes digital noise on input channels

Sorry, and to be clear...I'm using a single interface...either the Apollo x16 OR the Apogee Symphony. This happens when I'm using these one at a time as my playback engine.
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Old 08-04-2022, 07:38 PM
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Eric Lambert Eric Lambert is online now
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Default Re: Changing outputs during playback causes digital noise on input channels

Do you ever experience this issue when switching with playback stopped?

I can't say that this is a new one, though I've come across it so rarely that I've never figured out exactly what caused it. I'm guessing I would have increased the buffer size, which tends to give PT more breathing room to handle tasks like this, and I'm guessing that it worked because I can't recall any further troubleshooting afterward.
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Old 08-04-2022, 07:43 PM
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Eric Lambert Eric Lambert is online now
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Default Re: Changing outputs during playback causes digital noise on input channels

Just thinking more about how it's only occurring on channels 3/4 and not 1/2... maybe it's related to a brief confusion of sync. How are your interfaces transmitting/receiving clock to/from ProTools?
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Old 08-04-2022, 07:52 PM
Darryl Ramm Darryl Ramm is online now
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Default Re: Changing outputs during playback causes digital noise on input channels

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Originally Posted by Eric Lambert View Post
Do you ever experience this issue when switching with playback stopped?

I can't say that this is a new one, though I've come across it so rarely that I've never figured out exactly what caused it. I'm guessing I would have increased the buffer size, which tends to give PT more breathing room to handle tasks like this, and I'm guessing that it worked because I can't recall any further troubleshooting afterward.
It is likely a Pro Tools bug, changing the sample rate just forces a partial reset of the interface. Increasing the buffer size might help avoid say CPU errors if they were happening but it should never behave like this. And we know there are other cases where just toggling IO buffer sizes fixes weird problems.

But hopefully input 3&4 here is not special in any way, no other use of that input, there is no way anything is feeding back etc... there is no hardware monitoring loops, etc. all stuff to check. (and swap 1&2 and 3&4 cables *at* the interface). But the use of different interfaces likely means many possible feedback paths and driver bugs have been excluded. If this is nicely reproducible please file a support case with Avid... who knows it might also uncover other problems folks run into where this type of behavior/change sample rate fix happens.
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Old 08-05-2022, 04:37 AM
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Default Re: Changing outputs during playback causes digital noise on input channels

First of all, changing outputs during playback is not a good idea if you have delay compensation on (and why would it be off). This has nothing to do with sampling rates or clocking per se, but a change in delay compensation always forces a reset to everything which is why you should do it with playback stopped.

Now if changing outputs during playback is essential to your workflow, you should turn off delay compensation and basically have all-avid interfaces which is a known quantity. Avid is not testing third party boxes.
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  #10  
Old 08-05-2022, 11:54 AM
krocksf krocksf is offline
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Default Re: Changing outputs during playback causes digital noise on input channels

Ya, I realize changing input/output assignments during playback is probably not a great idea, I just thought this behavior was interesting and over all not a great experience. Unfortunately I don't have an Avid interface anymore to test out if this happens there too.

I don't recall ever running into this before, so perhaps it's something in one of the newer releases. I was playing around with this more last night and it does not happen with playback stopped, so I guess the moral of the story is...don't change inputs/outputs during playback. :)

Thanks for all the responses guys.
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