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

[Dr Huge Longjohns]

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. )

[un_quantized]

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.

[Dr Huge Longjohns]

So you're using the track output rather than a send? That's interesting too, thanks!

[un_quantized]

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.

[muzines]

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.)

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.

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.

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.

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. )

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.

[Dr Huge Longjohns]

You are of course right, D! (I'm on 10.4.6 on High Sierra.)

Simple test to verify (I just checked with LPX 10.4.6)

I did this and, as you say, the CPU usage goes to zero.

So I'm at a loss to know how my experiments gave me such a clear result, but as you say, it may simply be that I had so many heavy duty send effects in place and fooled myself somehow with the freezing process on individual tracks.

What is interesting, though, and it was Waves Abbey Road Chambers that started this quest in many ways, is that even with no playback running, ARC is still using a massive amount of CPU. All tracks frozen, nothing playing, CPU is still huge. Using the Activity Monitor utility you can see Logic's CPU jump to 45 odd per cent when ARC is actually doing anything other than sitting there on an aux channel, and making it virtually unusable. Why is this?

The irony is, of course, that I now know I can bung it on every track as an insert and not use any CPU at all, in theory!

Also a giveaway here - you *can't* *switch off* plugins on a frozen track.

Actually, you can. You can deactivate them, remove them, or insert new ones while the track is frozen. Just hover over the plug in when it's in dark, frozen mode and you can turn them on or off or delete them. When the track is unfrozen the changes you made take effect. If you add a new one you get the 'plug in will be activated when needed' or whatever the message is. This is probably another reason I got confused????

Thanks for your help as ever D. Have no idea what gave me such an erroneous steer. Cheers

[muzines]

So I'm at a loss to know how my experiments gave me such a clear result, but as you say, it may simply be that I had so many heavy duty send effects in place and fooled myself somehow with the freezing process on individual tracks.

Yes maybe. It's certainly less than obvious what may be going in complicated projects - which is why if in doubt, it's best to start with an empty project and test there first.

What is interesting, though, and it was Waves Abbey Road Chambers that started this quest in many ways, is that even with no playback running, ARC is still using a massive amount of CPU. All tracks frozen, nothing playing, CPU is still huge. Using the Activity Monitor utility you can see Logic's CPU jump to 45 odd per cent when ARC is actually doing anything other than sitting there on an aux channel, and making it virtually unusable. Why is this?

Likely because some plugins will be running all the time. A plugin on a bus channel might have incoming audio at any moment, regardless of whether Logic is in playback mode. You could hit a note on a software instrument track, or feed in live audio from an input channel, or a record-enabled track, or Rewire etc.

I don't have that plugin - does the CPU performance behaviour differ if you put it on a regular audio track, as opposed to an aux channel?

Also a giveaway here - you *can't* *switch off* plugins on a frozen track.

Actually, you can. You can deactivate them, remove them, or insert new ones while the track is frozen. Just hover over the plug in when it's in dark, frozen mode and you can turn them on or off or delete them.

Ah Ok, that behaviour changed somewhere along the line, I just never noticed as I had ten years of knowing the previous behaviour, which was if you tried, Logic complained and wouldn't let you do anything. Hence I don't bother trying!

[Dr Huge Longjohns]

does the CPU performance behaviour differ if you put it on a regular audio track, as opposed to an aux channel?

Not really as far as I can see. Total mac cpu drain is around 52% with it on either a track or an aux. Two instances of ARC, either on two tracks or a track plus an aux crashes Logic instantly with CPU up to 106% at least. There's a lot of chatter on the net about its CPU drain, AR Plates too which I don't have.

But it sounds amazing, especially as I got it for $29 in a Waves sale!

[muzines]

does the CPU performance behaviour differ if you put it on a regular audio track, as opposed to an aux channel?

Not really as far as I can see. Total mac cpu drain is around 52% with it on either a track or an aux.

It's using half a core on an audio track, even with Logic stopped? This shouldn't happen - unlike auxes/outputs, Logic knows when audio is coming through or not on an audio track, and intelligently turns plugins on or off.

Of course, when processing, the CPU load would be the same (it's doing the same work), but the difference is that auxes/outputs are using CPU all the time, but an audio track should only use it when something is actively being processed (ie, Logic is in playback, and there is audio data in the track at that point - or you are input monitoring a live input).

Two instances of ARC, either on two tracks or a track plus an aux crashes Logic instantly with CPU up to 106% at least.

I don't see why that should crash Logic, as long as each instance gets assigned to different cores. You may though have a problem in live mode as stuff may be smooshed onto one core in this case, so you can use low latency mode to keep this under control while tracking...

[Dr Huge Longjohns]

Well it's pretty clear! So here's Logic with both instances of ARC switched off, see CPU and Activity Monitor.



Switch on ARC on both, NO audio playing, Logic stopped. As you can see ARC is using massive CPU even though it's not even processing anything.

[muzines]

Yes, but you're switching on the bus version as well in the second pic, so of course CPU will be consumed - you're seeing the CPU use from the bus instance.

As we've said, bus plugins will generally consume CPU all the time, regardless of whether Logic is playing, but audio tracks won't - they'll only process in playback and while there is audio to process. In your second example, with Logic stopped, if you'd only enabled the instance on the audio track, *not* the aux channel, you shouldn't see the CPU rise.

[Dr Huge Longjohns]

Here you go. ARC just on track, no playback, big CPU usage.

[muzines]

Here you go. ARC just on track, no playback, big CPU usage.

Hmm...

And relating to points made above - does it still do this in a blank project with one ARC on an audio track, no playback or input monitoring?

[Dr Huge Longjohns]

Short answer, yes. BUT, and this is progress I guess, I've discovered it ONLY does it on midi tracks, not audio.

[muzines]

Short answer, yes. BUT, and this is progress I guess, I've discovered it ONLY does it on midi tracks, not audio.

Software instrument tracks are a little different. When not selected, they behave like audio tracks, and only process audio (during playback) when there is stuff to process.

However, when selected, the instrument track is put in live mode, and all plugins on that channel, and any auxes it feeds, are all shifted onto one core and activated (as you can play a note at any time.)

So, it all seems like Logic is acting normally, which is reassuring!

[Dr Huge Longjohns]

So is this normal? Play midi track with ARC, loads of CPU hit. As you say, track active but not playing, loads of CPU. Track not active, CPU drops away. Switch track to active, no CPU until you hit play?

[muzines]

So is this normal? Play midi track with ARC, loads of CPU hit. As you say, track active but not playing, loads of CPU. Track not active, CPU drops away. Switch track to active, no CPU until you hit play?

Plugins on tracks in Logic only consume CPU for plugins when they are actively processing audio. This means either in playback, where there are MIDI notes or audio data on the track, and/or when the track is actively doing something (eg, a software instrument track is selected for live real time playing, or an audio channel is in input monitor mode or recording).

Auxes, outputs, input channels etc are always active and so plugins on them will always be processing and therefore consuming CPU.

Logic tries hard to optimise CPU use, to deactivate plugins where they are not required, but at the end of the day, if you are whacking on heavy CPU plugins, then when that processing is required, it's going to be a heavy CPU hit.

The biggest factor is software instruments when the track is selected, as for efficiency and latency reasons this forces all the plugins on that track, *and* other plugins in use (eg, plugins on any auxes that the software track feeds, and outputs), get forced onto the *same* CPU core. Depending on your plugins and projects, this can require more processing than a single core can provide (even though you may well have other cores completely inactive). In these cases, you can turn off plugins temporarily, and/or use Low Latency Mode.

[Dr Huge Longjohns]

this forces all the plugins on that track, *and* other plugins in use (eg, plugins on any auxes that the software track feeds, and outputs), get forced onto the *same* CPU core.

So does Unquantized's suggestion earlier in the thread move the plugin processing to two different cores? ie sending the track to a new track via its outputs?

[muzines]

So does Unquantized's suggestion earlier in the thread move the plugin processing to two different cores? ie sending the track to a new track via its outputs?

As previously said, in Live mode, *all* plugins that the live track requires are moved onto one core.

If you've split your plugin processing up into three tracks and auxes to help distribute the load across cores in playback, *all* those plugins will come back onto one core in Live mode. This is why I said that it can be problematic if you have channels that require more processing than one core alone can handle, because in Live mode you'll likely CPU overload Logic which will complain.

When you deselect the track, it comes out of Live mode, and plugins on different channels are distributed among other cores as Logic decides.

[Dr Huge Longjohns]

OK, I'm with you. Thanks for all your input, very interesting thread, for me at least!

[ManFromGlass]

Interesting for me as well. I was having a similar problem with some of the patches from the Kepler instrument. It appears that my old tower with maxed out ram and 12 cores just can’t handle some of the demands of some of the new generation plugs and instruments.
The Spitfire people were very helpful in getting me sorted.