Operation is possible with rekordbox but the sound is not output (The DDJ-400 is not recognized as the audio device).

(1) Check whether or not the TRIM control, channel fader, crossfader, MASTER LEVEL control, EQ control, and FILTER control are at appropriate positions.
For details, refer to the FAQ “Troubleshooting -No audio”

(2) If multiple USB devices (mouse, keyboard, etc.) are connected to the same USB bus system on the computer or to a USB hub, correct operation may not be possible due to problems of the USB bus' band or compatibility between USB devices.
In this case, the problem can sometimes be solved by changing the connected USB port.

(3) Are this unit and the computer connected properly with a USB cable?
This unit and the computer need to be connected properly.

(4) Is the rekordbox software latest version?
If you are using rekordbox Ver.4.x or earlier, download latest rekordbox from rekordbox.com.
If rekordbox Ver.5.x is already installed, update rekordbox to the latest version using the Update Manager which is shown when starting rekordbox.

For the most recent information on the supported operating systems, check rekordbox.com.
http://rekordbox.com

For details, refer to “Installing rekordbox” in the Operating Instructions.

(5) Are terminals or plugs dirty? Wipe any dirt off terminals and plugs before making connections.