Playback and Recording : Record Setup : Selecting a Record Input Monitoring Mode : Selecting a Record Monitor Mode

Selecting a Record Monitor Mode
For record-enabled tracks to use Auto Input Monitoring:
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Select Track > Auto Input Monitoring.
For record-enabled tracks to use Input Only Monitoring:
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Select Track > Input Only Monitoring.
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To toggle between Auto Input and Input Only monitoring, press Option+K (Mac) or Alt+K (Windows).