When using the SL 1 or TTM 57SL on Mac, Scratch Live does not work with a USB buffer setting of 1 (the minimum). This issue is due to limitations of Mac OS X and how it handles USB 1.1 audio devices.
Note: This problem does not effect the SL 2, SL 3, SL 4 and Sixty-Eight, as they are USB 2.0 devices.