Donning my good pro-sumer headphones with nothing else but power connected to the DDM4000, I proceeded to search every nook and cranny for internal noise like a bloodhound tracking game. As you might expect from something that touts itself as a 24-bit mixer, there isn’t much to be found within reasonable limits. With the headphone volume all the way up, I heard a slight constant whine around 13kHz (with a harmonic at 1kHz) even with everything turned down. It seems to be related to the microphone input because while the good news is that this whine is not persistently present in the master output, it appears when I enable the mics, and I can adjust the whine with the mic EQs. It’s not affected by the gain controls, which is interesting. There is also a really slight 50Hz (AC mains) buzz on channel 4 in line mode, which makes sense since it’s right next to the mains power input, but it’s so slight that you can just barely hear it, and that’s only after the gain and EQ knobs are all the way up on that channel as well.
The Line inputs have very little noise. I had to turn the gains and EQs all the way up to hear any, though the dedicated (non-switchable) line inputs are slightly quieter. The phono inputs are quite noisy by comparison, but that stands to reason considering the order-of-magnitude greater pre-amplification they must do. And to be fair, they quiet down a lot when they’re actually connected to a turntable.
Please take this noise analysis as more academic than anything, because in nearly all practical cases, these internal noise levels are lower than those of most DJ source equipment (unless you DJ from audiophile-grade CD players) so none of this is detectable in practice. (For example, when I connected and turned on my X^2s, the noise level on the line inputs rose almost to the unconnected-phono level, so the mixer’s internal noise floor was already way below that of my decks and therefore not a factor.)
The DDM4000 features pre-fader VU meters on each channel that have a good dynamic range represented by seven segments which go from -20dB to +9dB, and clipping occurs a little above that. It’s easily possible to clip the input stage with the gain range given to you, so set your levels carefully, and do it each time you change songs! (Basically, if you regularly see more than one red LED, the level is too high.) The channel VU meters are also pre-EQ, which is different from the DJM-500. (This might suggest that the EQ is done in the digital domain.)
The master VU meter shows a range of -24dB to +12dB plus dedicated Clip LEDs. (I think the dynamic range is the same as on the input stages, you just have more LEDs on the master output for detail.)
I covered usage notes for specific controls in the above section, but in general, the DDM4000 is pleasing and fun to use and it works reliably. The light faders and their caps feel great. The hard plastic buttons all have a distinct click so you can tell by feel if you’ve pressed one. The extra controls are intuitive, though the effects section takes a bit of time to figure out simply due to the sheer amount of customizability in the limited space. I was able to figure out most of the additional controls without having to look at the manual after several minutes of playing around with them. This, and the fact that there are eight user preset save slots should put club owners at ease if they choose this mixer for the installed system, as any DJ who has ever used a four-channel DJ mixer will already know their way around the essential features of this one, and resident/frequent DJs can each customize the settings as they wish. Of course I strongly encourage reading the manual in any case so you can get the most out of all of the extra features the DDM4000 brings.
While I was sniffing around for sound quality issues, I noticed that the headphone output clips well before the master output does. This might be a cost-conscious move, since you of course want the best sound on the floor and dynamic range doesn’t matter as much in the headphones, but it’s also handy to give you additional early warning that your channel gain levels are too high so you can fix them before the crowd hears the mess. (There’s no headphone clip indicator, it just starts to sound bad.)