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-RX3. Here are some more details:

・ You can record the sound to a USB flash drive or HDD connected to the USB 2 port.
・ 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 recorded file name will be “RECxxx.WAV” (xxx is a 3-digit number).
・ The maximum number of recorded files is 999.
・ Adjusting the MASTER LEVEL doesn't affect recording.

Note: Because this unit doesn’t have a clock, the recording time and date aren’t registered on the storage device (USB).