I have a Focusrite Saffire PRO24 connected to my MacBook Pro 13" 2015 (10.12.2) as an external sound card. When using rekordbox I use the PC Master Out feature to send the audio to this sound card. I'm using current rekordbox software (5.2.2)
I have been using this setup for 4 months now and its been fine, but today the audio started distorting/crackling. It starts a few minutes into using software and gets worse over the next few minutes. If I click PC Master Out, off then back on again, it seems to reset, starts fine and then distorts again. This distorting hasn't happened with my built in speakers or Master Ouput from DDJ-SX.
The sound card works fine, as this doesn't happen when I use it with iTunes, only recordbox.
I haven't recently changed my buffering settings, as these are setup correctly.