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Logic: freezing doesn't freeze! CPU save trick!

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Logic: freezing doesn't freeze! CPU save trick!

Postby Dr Huge Longjohns » Thu Sep 12, 2019 5:09 pm

I've been having lots of problems with high CPU in projects that at face value shouldn't be overly taxing for Logic on my well-specced Macbook (16gigs of ram etc). I've had projects recently where every track is frozen but still getting huge cpu spiking, to the extent that opening a new plugin window or switching to the mixer view would crash Logic instantly.

So I've been doing a load of experiments and discovered something new to me. This may be a 'of course it does that, you silly fool, Longjohns!' moment for all of you but just in case, I thought I'd post here.

So what I realised/discovered is this: if you freeze a track eg an EXS24 synth with a heavyweight plugin on, the synth and plugs carry on using loads of CPU even though you've rendered the audio. I couldn't understand why my projects were still using huge power even though literally every track was frozen. (And this is with the full green freeze before you jump in with 'you must be using the blue pre-plugs freeze, old boy!')

So what you have to do is you freeze the track then switch off the plugins and instrument and, bingo, super-low CPU usage. Alternatively you can bounce in place, of course, and then switch off the plugs and instruments on the original track or delete them completely.

As I say, if this is old news to everyone, Sorry! Game changer for me, though. (Although Abbey Road Chambers is still virtually unusable if you have it on a send. :roll: )
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Re: Logic: freezing doesn't freeze! CPU save trick!

Postby un_quantized » Mon Sep 16, 2019 9:33 am

Thanks, this is handy to know as I have had similar problems.

It doesn't completely help as I like to have the plug-ins active for further tweaks on the frozen audio.

Another trick I found that helped with CPU spikes is to move plug-ins from the actual track to a new bus, then route the track output to the bus. In the CPU meter you can see that the load is often on one or two cores, this trick seems to re-distribute the load.
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Re: Logic: freezing doesn't freeze! CPU save trick!

Postby Dr Huge Longjohns » Mon Sep 16, 2019 10:00 am

So you're using the track output rather than a send? That's interesting too, thanks!
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Re: Logic: freezing doesn't freeze! CPU save trick!

Postby un_quantized » Mon Sep 16, 2019 12:52 pm

Dr Huge Longjohns wrote:So you're using the track output rather than a send? That's interesting too, thanks!
No, not to replace sends.
When a track gets loaded with some thirsty in-line plug-ins in the Audio FX area, copy all of these to a new bus and send the output of the track to the bus. For some reason this shifts the load around the CPU cores.
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Re: Logic: freezing doesn't freeze! CPU save trick!

Postby desmond » Mon Sep 16, 2019 5:58 pm

Dr Huge Longjohns wrote:So what I realised/discovered is this: if you freeze a track eg an EXS24 synth with a heavyweight plugin on, the synth and plugs carry on using loads of CPU even though you've rendered the audio.

What OS and Logic versions are you running there?

The *whole point* of freezing is to turn off CPU processing, in favour of a rendered audio file. As soon as you freeze a channel (normal freeze mode), then all plugins on that channel will be turned off, and not consume CPU.

(They will still consume RAM, but the latest Logic versions offer some streamlining for this.)

Dr Huge Longjohns wrote:I couldn't understand why my projects were still using huge power even though literally every track was frozen. (And this is with the full green freeze before you jump in with 'you must be using the blue pre-plugs freeze, old boy!')

Can you provide a simple, reproducible example of this?

The only thing I can think of is that plugins on busses, inputs, and outputs remain live - these can't be frozen, so if you have tracks sending to multiple heavy AUX channels with lots of plugins, those will continue to use CPU.

Dr Huge Longjohns wrote:So what you have to do is you freeze the track then switch off the plugins and instrument and, bingo, super-low CPU usage.

I have never had to do this with any version of Logic since freeze was introduced to reduce CPU. And my first Mac version of Logic was on a PPC Powerbook - not exactly a machine known for it's abundant CPU - so I had to use freeze *a lot* with software instruments.

Also a giveaway here - you *can't* *switch off* plugins on a frozen track. Logic won't let you. So if you are able to switch off plugins *after* you've frozen a track on that channel, then you haven't frozen that track (or maybe have frozen the source-only) mode.

Dr Huge Longjohns wrote:Alternatively you can bounce in place, of course, and then switch off the plugs and instruments on the original track or delete them completely.

Sure.

Dr Huge Longjohns wrote:As I say, if this is old news to everyone, Sorry! Game changer for me, though. (Although Abbey Road Chambers is still virtually unusable if you have it on a send. :roll: )

Simple test to verify (I just checked with LPX 10.4.6)
- Load up an ES2, and chuck some additional plugins like a Space Designer and Step FX plugin.
- Record some chords.
- Select a different track than the ES2 track to get it out of Live mode. Watch the CPU meter during playback to confirm the CPU use.
- Now freeze the ES2 track (normal, Green pre-fader freeze)
- On the next playback, *no* CPU is consumed, as those plugins are no longer active - Logic is simply playing the freeze file. You'll see an increased Disk I/O as a result.
- Turn freeze off for that track, resume playback, and watch the CPU meters show CPU consumption again.

This is how Logic has always worked, and if you're not seeing this, then something strange is going on, or you're not describing the behaviour or setup somehow.
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