Native Instruments MASCHINE MK3 Getting Started page 168

Using Advanced Features
Using Other Sound Sources
4. Make sure that Maschine In 1 L and Maschine In 1 R in the left column are assigned to
the pair of inputs 1: Input Left and 2: Input Right of your controller in the right column
— this is the case by default.
MASCHINE - Getting Started - 168