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TR-Rec is short for TR Recording. One of the Roland Corporation TR-Series drum machines, like Roland TR-808 and Roland TR-909 had these control features. TR-REC mode lets you turn the desired notes on and off using the PADS on the Roland MC-303, Roland MC-307, Roland MC-505, Roland D2, Roland MC-909 and the new Roland MC-808. You can see the notes onscreen or on the pads as you work.