Logic Pro X Jitter & Lag Using Logic Pro X for Livestream Mix

logicuser

New Member
I am trying to determine the root cause with jitter (seems like clicking noise due to dropped packets) and lag (time between live sound occurs and the output from Logic) using Logic Pro X to mix music for real-time livestream. I am using Logic Pro X as a mixing console (lots of instruments/vocals, aux channels with plugins for EQ, compression, de-esser, autotune, reverb, delay, etc...). I am taking all my inputs (30+ input channels) from our Soundcraft Si Impact digital mixing console via USB interface. I am not recording, only mixing with about 40-50 tracks (input channels + auxiliary bus channels). I have Software Monitoring enabled and sending the audio output to our Boxcast livestream.

About a year ago, we were using this setup weekly. But then I started to have issues. I was running Logic Pro X on a MacBook Air. It got to the point it was so unusable I went back to old school approach and took our livestream audio feed directly from our sound board (but this does not provide the benefits we get with Logic Pro X plugins).

We ended up upgrading to a MacBook Pro and the problem went away (at first). However, this issue has started again. It started out as a few clicks here an there in the output, but has been recurring more frequently lately. It does not happen always, but when it does occur, the lag seems to increase gradually during the 40 minute session (after 40 minutes the lag is about 500 to 1000ms). And at times, a harsh clicking noise is introduced, sometimes in short bursts, and other times continuously. This seems similar to jitter you might experience with audio over a bad network connection (i.e. VOIP, etc..), although there is no "network" in my setup (unless you consider the data transfer via the USB interface from my soundboard to the MacBook Pro).

I have tried to experiment with Logic Pro Audio Preferences (IO Buffer size, Recording Delay, Processing Threads, etc...) but have not found anything to reliably solve this problem. At one point I even had the Soundcraft team investigate (they were responsive and did some testing, but no smoking gun - so I upgraded from MacAir to MacBook Pro).

Disconnecting the Soundcraft USB audio interface, and reconnecting it will reset things back to normal. As I am producing live music for livestream, this is not really an option.

Last week I paid special attention to the Processing Threads & Drive I/O during our performance. Processing threads were utilized between 25 - 80%. I found it interesting that only 8 of 16 cores were utilized. Maybe this is normal. Drive IO was almost 0% (not surprising since I am not recording - only mixing).

I am curious if anyone has a similar use case or setup with good results. Any suggestions to troubleshoot? Any best practices on using Logic Pro to produce a livestream mix?
 

fuzzfilth

Logician
What you describe is hinting at short periods of processor overload, which you might not even see on the performance meter, yet it is enough to accumulate over a long period of time.

Mixing 50 channels, with plugins, in 'real'time is taxing on any system, even just the attempt to do this on an Air is crazy. What's the data on the Macbook Pro ?

Autotune, AdLimiter, Multipressor and any phase linear stuff add lots of latency for lookahead, which will tempt you to turn the buffer down, thus taxing the processor even more, (good) reverbs will add even more load.

Using USB for audio is also not a low latency solution like Thunderbolt is. Quite possibly the USB device is class compliant, as in you didn't have to install extra drivers for it, so it's not optimized towards highest performance/shortest latency, however, it should be reliable, yet here we are.

A few things to try:
- remove all plugins so only the bare channel/bus/aux/mix rounting is left. Does this run fine ? If yes, you're using the wrong, too many and/or too heavy plugins.
- set the IO buffer to 512 or 1024. Does this run fine ? If yes, set up a video delay in the streaming software to compensate the high (but constant) latency you will be getting.
 
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logicuser

New Member
fuzzfilth... Thanks for the tips and quick response.

MacBook Pro (16 in)
16GB memory
8-Core Intel i9 2.3 GHz
256k L2 Cache, 16MB L3 Cache
Hyper-Treading Enabled
macOS Big Sur 11.2.3

First I will experiment with the plugins. Does it make a difference if I remove the plug-in vs disabling it?

I will also check the IO buffer.

I'll report back in a few weeks as we have a few weeks off.
 
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fuzzfilth

Logician
Basic troubleshooting rule: simplify as much as possible unless you want to keep guessing.

If you can make your routing and number of channels work without any plugins, then good, that's a very solid starting point, and it proves that indeed the plugins were the cause of the problem. Now you can cautiously add plugins back in, a couple at a time and see how far you can safely take it without popping the balloon.
 
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