Is there a way to arm a track from the keyboard in Cakewalk Sonar?

Yes, you can assign a key binding for this function. Here's how:

Go to Options - Key Bindings, select the keyboard key (on the left) to assign to Track | Arm for Recording (about 3/5 of the way down the list on the right), and click Bind.

Sonar will now record-enable or un-record-enable whatever track is selected in yellow when you press the assigned key.

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