Communication problems between Carbon and Pro Tools

[michenal]

Hi there,

I have received Carbon a few weeks ago and I really love it for its sound and the workflow!

I have run into persistent connection issues, however, between Carbon and Pro Tools recently. I am wondering if I am alone or if it's a widespread issue that will hopefully be resolved in future firmware/software updates.

I have a pretty powerful new Mac Pro with 16 cores, lots of RAM and large fast storage space with MV2 SSDs etc.., but somehow, it seems that the issue arises whenever the audio engine struggles to keep up at low buffer settings, especially when using CPU intensive virtual instruments but also when working on large sessions with many native plugins. Instead of getting the usual CPU overload errors that would sometimes stop playback but be inconsequential with my other audio interfaces (Metric Halo 3D), with the Carbon interface, I get the following message:

“Pro Tools cannot communicate with the Selected Playback Engine device. Please quit Pro Tools, reconnect the unit, and then relaunch Pro Tools.”

I then need to quit Pro Tools and restart it to be able to work in my session again. This situation has happened a lot lately, as I am working more with orchestral virtual instruments for my new project.

I am wondering if I should open a ticket or whether I should just be patient and wait for a new firmware release. My Carbon interface is connected straight into the Ethernet port using the provided cable. I should clarify that I am not using an aggregate playback device, just Carbon in my sessions.

Anyone else here has encountered these issues? Do you think it’s a hardware issue and that I should open a support ticket?

Thanks!

Sebastien

[Kyle Splittgerber]

Hey Sebastien,

Congrats on the purchase. Sorry to hear about the issues.

What macOS version are you running?

What HW Buffer size(s) are you using when you notice this issue?

Is "Optimize Performance at Low Buffer Sizes" checked in the Playback Engine? Does it make any difference if you change that setting?

Have you changed the Carbon AVB configuration in Audio MIDI Setup yet? Default is 28x56 channels.

Thanks,

Kyle

[michenal]

Hi Kyle,

Thanks for taking the time to reply.

I am using Catalina 10.15.7 and I have had issues at 32 and 64 samples buffer (I have not tried higher buffers as the VIs are not responsive enough for what I am doing).

"Optimize at Low Buffer Sizes" is ticked when I have the issue. I just tried unchecking this option, and it seems to lower occurrence of the communication problems I described. This seems counterintuitive but it seems to work. Thanks for the suggestion!

I have not changed the AVB configuration in Audio Midi Setup. I do not see how I can do that other than changing the clock source or the sample rate. The interface shows the correct 28x56 channels.

Thanks!

Sebastien

[Kyle Splittgerber]

Originally Posted by michenal

Hi Kyle,

Thanks for taking the time to reply.

I am using Catalina 10.15.7 and I have had issues at 32 and 64 samples buffer (I have not tried higher buffers as the VIs are not responsive enough for what I am doing).

"Optimize at Low Buffer Sizes" is ticked when I have the issue. I just tried unchecking this option, and it seems to lower occurrence of the communication problems I described. This seems counterintuitive but it seems to work. Thanks for the suggestion!

I have not changed the AVB configuration in Audio Midi Setup. I do not see how I can do that other than changing the clock source or the sample rate. The interface shows the correct 28x56 channels.

Thanks!

Sebastien

Ok, glad that improved things! There are cases where that setting helps, which is largely dependent on what the plugins are doing in the session. But, there are cases where it doesn't. So, I'd suggest leaving it unchecked and letting us know if the errors come back.

Regarding configuring AVB channels, see pg 41 in the guide here. You don't need to change that unless you are running out of input or output channels in Pro Tools. You can keep an eye on how many of those channels are used in the System Usage window. And, Pro Tools will post an error when you run out. But, depending on your workflow that may never happen.

[michenal]

Thanks Kyle,

I can see that now, thanks for pointing this out. I must confess I had not read the appendix of the manual yet .

One quick question related to this. Can I expect to improve performance and reduce the likelihood of my connection problems if I reduce the number of outputs to my lower current needs (e.g. 24 channels would currently be enough to sum my mixes on my mixing console)?

On another note, I am surprised Carbon users have access to 56 outputs. Pro Tools used to be limited to 32 outputs and if I am not mistaken, Carbon does not allow to output more than 36 channels. At the moment we are limited to 8 analog outs + 2 monitor outs + 4 stereo headphones + 16 through ADAT so we cannot currently output more than 34 channels at 44/48k. Are the additional 22 channels provided for internal digital routing within the computer only or are they eventually going to be accessible physically through the second ethernet port on Carbon?

[Kyle Splittgerber]

Originally Posted by michenal

Thanks Kyle,

I can see that now, thanks for pointing this out. I must confess I had not read the appendix of the manual yet .

One quick question related to this. Can I expect to improve performance and reduce the likelihood of my connection problems if I reduce the number of outputs to my lower current needs (e.g. 24 channels would currently be enough to sum my mixes on my mixing console)?

On another note, I am surprised Carbon users have access to 56 outputs. Pro Tools used to be limited to 32 outputs and if I am not mistaken, Carbon does not allow to output more than 36 channels. At the moment we are limited to 8 analog outs + 2 monitor outs + 4 stereo headphones + 16 through ADAT so we cannot currently output more than 34 channels at 44/48k. Are the additional 22 channels provided for internal digital routing within the computer only or are they eventually going to be accessible physically through the second ethernet port on Carbon?

The way AVB works on the Mac is that all channels within a stream are active, regardless of whether or not those channels are used. This means the the Mac CPU usage is based on stream count and not channel count. A stream is essentially like a folder or pipe for the channels. With Carbon, we use 28 channels per stream for the 44.1-96 kHz configurations. And, 14 channels per stream for 44.1-192 kHz configurations. This allows the user to tune things a bit to find the best balance between sample rate(e) needed, channel count needed, and CPU impact. For your case, if you are not running out of channels with the 28x56 configuration and don't need to go above 96 kHz, then there's no reason to change anything. It won't improve performance.

Regarding channel count, traditionally an audio interface will have a 1:1 mapping relationship between hardware input/output and DAW input/output. However, with DSP Mode tracks, Carbon can use more channels (via AVB) than the 1:1 hardware mapping that you might be used to. So, yes your hunch is correct that those additional channels are for internal digital routing needs. And, depending on how complicated your session is, you may need more channels. If that ever happens, then you'll want to go to AMS to increase the AVB configuration.

That help clear things up?

Also, I'll send you a direct message about digging in a bit deeper regarding the errors you were seeing at low buffer sizes.

Thanks.