THE CONTROLLER IS
MAKING NO SOUND

Open your DJ software's preferences and look at the audio page. The controller has to be selected there, and the master and headphone outputs have to be pointed at its own master and headphone channels. If the box is showing your laptop's built-in output, or a pair of headphones you plugged in last week, the controller is silent and there is nothing wrong with it.

This is also the reason the same controller works at home and not at the venue. Plugging in an HDMI screen, a dock or a USB headset can hand the software a new default audio device without saying so.

This is the part that is repeated wrongly nearly everywhere. The standard advice for a silent controller is to reinstall the audio driver. On a lot of modern units there is no driver to reinstall, and a DJ who spends the evening looking for one is chasing something that does not exist.

AlphaTheta publish it as two separate procedures in the same document.

• Units with no driver. AlphaTheta publish this as two different procedures, and the difference is whether the unit uses a driver at all. For the DDJ-FLX4 on Windows there is nothing to install: "Select DDJ-FLX4 (DDJ-FLX4 WASAPI) connected to your PC", with "Master Output :DDJ-FLX4 WASAPI:MASTER" and "Headphones Output :DDJ-FLX4 WASAPI:PHONES".
• Units with a driver. For a unit that does use a dedicated driver, the same document names it explicitly: "Select the driver software for the DDJ-FLX10 (DDJ-FLX10 ASIO) connected to your PC", with "Master Output :DDJ-FLX10 ASIO:MASTER" and "Headphones Output :DDJ-FLX10 ASIO:PHONES". If that entry is missing from the list, AlphaTheta send you to Device Manager to check the driver installed at all.

So before you download anything, find out which of those two your unit is. Your model's page in this catalogue, and the download page on the maker's own site, will tell you whether a driver exists for it at all. If none is published, the driver is not your problem.

All four are AlphaTheta's own, and all four look normal from the front of the unit.

• The master attenuator, which lives in software. One of AlphaTheta’s causes for silence lives in software rather than on the unit, and almost nobody looks there: "Is the master output attenuator level set to -6 DB? Switch the master output attenuator level in [Preferences] of rekordbox."
• The input selector on the channel. The mixer section of a controller has an input selector per channel and it can be pointed away from the computer: AlphaTheta ask "Isn’t the input selector switch in the mixer section set to [LINE] or [PHONO/LINE]? Set it to [USB A] or [USB B]".
• Two gain controls inside the software. Two software levels can silence a controller that is otherwise perfect, and AlphaTheta name both: "Aren’t [Track Gain Adjust] and [Master Output Level Adjust] on rekordbox set to the minimum position? Adjust them to the appropriate position."
• The dirty terminal, last on their list and last on yours. AlphaTheta finish where a DJ would never start: "Are terminals or plugs dirty? Wipe any dirt off terminals and plugs before connecting."

And set your levels by the light, not by the position. AlphaTheta tie both level controls to an indicator rather than a position, which is the only way to check them in the dark: set TRIM "so that the orange indicator of the channel level indicator lights", and set MASTER LEVEL "so that the orange indicator of the master level indicator lights". That is a check you can do in a dark booth, which is more than can be said for twelve o'clock.

If the controller plays fine into headphones or speakers but the laptop itself has gone silent for everything, including video and music outside your DJ software, the controller is the cause and it is not broken.

A laptop that has gone silent everywhere, not only in rekordbox, has a documented cause and it is the controller. AlphaTheta ask you to open "Control Panel" - "Hardware and Sound" - "Sound", check whether the unit is selected as the default device, and if it is, "click a sound device other than the DDJ-400" and set that as default instead.

And if you are using the feature that sends the master to the laptop's own speaker, there is a second thing worth knowing before you decide it is faulty. PC MASTER OUT sends the master to the computer’s own speaker, and AlphaTheta answer the complaint that follows it plainly: the MASTER LEVEL knob does not govern that output. "Please adjust the volume of the computer built-in speaker at the computer’s volume setting."

Practising through laptop speakers is fine. Playing a gig through them is not, and the reason is not volume: you cannot hear a cue in headphones and a master on the same speaker at the same time.

If the unit is making no sound and the jog wheels and faders do nothing in the software either, stop looking at audio settings. This is a different fault and AlphaTheta ask three questions in order.

When the unit is silent and also unresponsive, AlphaTheta ask three things in order, and the second is the one a laptop DJ never thinks of: check the startup illumination when the controller is powered on, then "Check the power supply shortage of the controller. Connect an AC power cable to your PC if it is a laptop", then "change USB ports on the PC or replace the USB cable and reconnect it".

The middle one is the one to read twice. A laptop running on battery throttles what it delivers over USB, and a bus powered controller is the first thing to suffer. It presents as a unit that worked yesterday and is dead today, and the fix is a mains cable in the laptop.

The third one is worth doing properly too: the cable that came in the box is the first suspect, and a USB hub between the two is the second. Plug the controller straight into the computer.

Two things, in this order, and both take under a minute.

One. Open the audio preferences and confirm the controller is the selected device. That is the fault about three quarters of the time and it is a two click fix.

Two. Put the laptop on mains power, take out any USB hub, and use a different port. That covers the whole power and cable family in one move.

If neither works, the controller is not coming back in the next ten minutes. Every venue with a booth has an input you can reach: a laptop headphone output into a spare channel gets you playing, with no cue and no EQ, while you sort it out. It is an ugly set and it is a set.