Switching between USB/PC and CD modes is straightforward enough using the dedicated Source Select buttons. I tested the CDJ-400 with a couple of different USB keys, an iPod video, several MP3 CD-ROM disks and some standard audio CDs, and it performed without a hitch. I did experience slightly longer start-up times when using a USB device, typically between 10-15 seconds, compared to around four seconds for CDs, but overall the unit felt very responsive in use. And as we've come to expect from Pioneer, sound quality from the CDJ-400 is excellent with kicking tracks like Armand Van Helden's U Don't Know Me sounding dynamic and punchy without any harshness at the top end.
The other main controls are all where you'd expect them to be. The Tempo slider on the right hand side has a lovely smooth feel to it with a nice centre click. Its range can be toggled through ±6, ±10, ±16 and ±100% (the latter strangely referred to as WIDE) using the Tempo button, although if you're using MP3s the WIDE option isn't available. The Master Tempo button, which maintains the original key of the music regardless of the Tempo setting, can also be found just above the main slider. The sound quality of the Master Tempo is first rate, with no obvious digital artefacts within the ±10% range at least.
Tempo resolution is also very good, with steps of 0.02% at ±6% range which is ideal for keeping those long beat mixes in sync. Otherwise the slider moves in steps of 0.05% when set to ±10 or ±16%, and steps of 0.5% when set to WIDE. One function that is missing is a ‘brake' effect that simulates the slow wind-down and start-up sound on a vinyl turntable, but you can always improvise using the Tempo slider in the WIDE mode.
To the left of the jog dial are the familiar Play/Pause, Cue, Search, Track Search and Reverse controls found on other Pioneer CDJ players. Turning the jog dial while holding down the search or track search buttons allows you to search much faster than normal. With the Auto Cue function enabled, the player automatically skips any silence at the start of a track and enters stand-by mode at the point when the music actually starts.