I'd like to know more about the MASTER REC feature.

Using MASTER REC, you can record the audio coming from the MASTER OUT of the XDJ-XZ. Here are some more details:

・ You can record the sound to a USB flash drive or HDD connected to the USB2 slot.
・ You can't record to a mobile device, such as an iPhone or Android device.
・ The recorded sound is saved in the [PIONEER REC] folder as a WAV (44.1 kHz/16 bit) file.
・ You can record approximately 90 minutes of audio for every available GB on a USB device.
・ The recorded file will be split after every three hours of recording.
・ The maximum number of recorded files is 999.
・ Adjusting the MASTER LEVEL and MASTER EQ knobs doesn't affect recording.