DRAG a blue disc AND DROP it on the turntable to get your base ready to play. Alternatively you can TAP on the turntable (this can be only done if there's no disc placed on the turntable)
Then you can start using your turntable. These are the available actions you can perform on the turntable by touching the disc placed on it:
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You can interact with both turntables at the same time if the device supports multi touch