Soloing tracks
Located next to the Mute button, the Solo button ( 
) allows you isolate tracks in a project during playback. When you click this button during playback, the corresponding track remains audible and all other tracks are muted. Clicking the Solo button a second time returns all tracks to their original levels in the mix.
You can also press X to solo a track or group of tracks.
Tip: Press Ctrl and click the Solo button to solo only the selected track (and restore any other soloed tracks). If the selected track is already soloed, press Ctrl and click the Solo button to restore all tracks.
Choosing a track’s input/recording device
The Record Device Selector button 
in a track header chooses the audio input that will be used to record to a track. You can click the Record Device Selector button to turn input monitoring on or off and choose a recording device:
For more information, see Recording Audio on page 179.
Monitoring track output levels
During playback, a responsive meter is displayed in the track header to monitor the track's output.
Horizontal meter
Vertical meter
Use Vertical Meters
from the shortcut menu)
When clipping is detected, the peak meter displays a red Clip indicator.
Working with groups of tracks
Select a group of tracks by holding the Ctrl key while you click the track header of the desired tracks. Now you can adjust the volume, panning, track color, and other track attributes simultaneously.
Using undo and redo
You have unlimited undo and redo capabilities in ACID. Each edit you perform in the project is added to an undo history, which allows you to quickly restore the project to any of its previous states. In addition, undoing an edit automatically places it in the project’s redo history where it can be quickly
Note: The undo and redo histories are cleared when you close the project or exit the application.
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