Avid, the maker of Pro Tools, have introduced Track Freeze in Pro Tools 12.4, this enables a one button freeze of the track and its contents to free up CPU power. With the same 'snowflake' button you can simply unfreeze the track and return it to its original state.

There's been a lot of questions about Track Freeze in Pro Tools 12.4 so here's everything you want to know.

What Gets Frozen?

Plug-ins and automation for all plug-ins(except for any plug-ins remaining active when using Freeze to Insert)
Clip Gain
HEAT(if set to pre-insert)
Elastic audio

However the following track controls are maintained and are not rendered with track freeze:

Volume
VolumeTrim
Mute
Pan
SendLevel
SendLeveltrim
SendMute
Plug-in automation for plug-ins that are not frozen (when using Freeze to Insert)

Editing Restrictions on Frozen Tracks In Pro Tools 12.4

Most editing functions on frozen tracks are restricted. If you want to edit a frozen track simply unfreeze edit and refreeze.

The following editing actions are not allowed on frozen tracks:

Editing clips or clip contents
Elastic Audio
AudioSuite rendering is disallowed on frozen tracks.
Tempo changes, Song Start changes, and enabling or disabling the Conductor Track are not allowed when there are frozen tracks in the session.
Insert and Cut Time operations are disallowed in a session if there are frozen tracks.
HEAT is unavailable for frozen AuxiliaryInput and Instrument tracks.
Instrument Tracks are removed from the MIDI Editor window while frozen and MIDI parameters including Real Time Quantize settings can- not be adjusted until the track is unfrozen.
Clips used on a source play list for a frozen track cannot be removed from the session until the track is unfrozen.

The Following Editing Actions Are Allowed On Frozen Tracks:

Editing and writing of all basic track automation parameters including sends.
Editing and writing of automation on unfrozen plug-ins as well as addition and removal of plug-ins on unfrozen inserts (when using the Freeze Up to This Insert functionality)
Changing the track output path.

Track Freeze Compatibility With Earlier Versions Of Pro Tools

Any frozen tracks opened in an earlier version of Pro Tools will return to their native state, in other words an instrument track will open with the VI and the MIDI data. See the images below.

The session in Pro Tools 12.4

The session in Pro Tools 11.3

Furthermore the files are created and kept in the Rendered Files folder.

Other Useful Things To Know About Track Freeze In Pro Tools 12.4

Track Freeze can work on Groups in Pro Tools so if you have a group selection made then Track Freeze will affect all tracks in the group. You can also select multiple tracks and freeze them at the same time.

What About External Hardware?

External hardware cannot be frozen using the Freeze feature, it shows itself as available on the track but as Freeze is using an offline bounce process then it simply freezes silence. To be honest as the point of freeze is to reduce or free up CPU load the need to freeze external hardware is not really going to help. Your best option if you want to print the external hardware is to use bounce in real time.

Freeze Or Commit?

The simple answer is that if you want to send your tracks to anyone else then the safest option is to Commit the audio of those tracks effectively making audio stems. These tracks do not rely on the user having the correct version of Pro Tools or the plugins you own.

Freeze is a simple and effective way to free up CPU power in Pro Tools, for example if you need to record a vocal on a session with 80 tracks of VIs and the buffer is set high then freeze all tracks, set the buffer low to record at low latency and then simply unfreeze the tracks to continue with the session.

You could of course freeze tracks as you built a session and then have almost 'unlimited' CPU power depending on your computer.