Editing : Edit Modes and Tools : Zoom Buttons : Audio and MIDI Zoom In and Out Buttons

Audio and MIDI Zoom In and Out Buttons
The Audio and MIDI Zoom buttons let you zoom in and out vertically on audio and MIDI data respectively.
 
 
To zoom in vertically for all audio tracks, do one of the following:
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Press Control+Alt+] (Windows) or Command+Option+] (Mac).
To zoom out vertically for all audio tracks, do one of the following:
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Press Control+Alt+[ or Control+Alt+] (Windows) or Command+Option+[ or Command+Option+] (Mac).
To zoom all audio vertically to show the default waveform height:
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Press Control+Alt+Start+[ (Windows) or Command+Option+Control+[ (Mac).
To zoom in vertically for all MIDI and Instrument tracks, do one of the following:
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– or – 
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To zoom out vertically for all MIDI and Instrument tracks, do one of the following:
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– or – 
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To zoom MIDI vertically to show all notes (lowest to highest) in MIDI and Instrument tracks:
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Press Control+Start+Shift+[ (Windows) or Command+Control+Shift+[ (Mac)
To zoom in or out vertically for a single MIDI or Instrument track:
1 Make sure the Track View is not set to Clips.
2 Select the Zoomer tool.
3 Hold Start (Windows) or Control (Mac) and drag upwards to zoom in, or downward to zoom out.