Adding here that you can indeed overdrive a mixbus while your master is green: if you don’t keep an eye on your inputs, let them run in the red and or are summing a whole lot of tracks, the mixer will distort before the master: running the master at, say, -30dB, will still output a distorted signal.
Good topic guys! Helpful stuff for beginners, instead of rant about features 
When you are still below 0dB and mixing a lot of tracks together, the distortion that occurs is caused by oversaturation. This is when a lot of frequencies start filling up the whole spectrum or a bigger portion of it in same volume, so the usable audio information gets lost, and whole mix starts to distort.
Yeah I can agree with that, when there’s a lot of frequencies filling up the whole spectrum. I never was a audio programmer in DSP related topic and disassembly engineer for audio hardware but it’s true that Everything that is stored within audio Spectrum has own memory space and/or codes that decode incoming tracks signal have own hardware specs?
I am not talking about the digital audio, I am talking about analog audio spectrum.
If I would have 2 exactly the same mixers, it means 2 separated Masters like multiple masters playing per one track can fix this issue?
No, the amount of frequencies overlapping and sitting right next to each other will be the same. From the sound design and mastering point of view when you mix certain parts of your track, you make space in audio spectrum for some instruments, by eq’ing and filtering certain parts in a way, to have transparent and clear sounding mix of all instruments. Otherwise the mix is oversaturated and muddy. With EQ You can lower the gain of certain frequency (or group of frequencies) to lower down the distortion and oversaturation in that part of the spectrum. Or You can filter out the overlapping frequencies and this way also avoid oversaturation and distortion.
Been following this topic a bit, but the topic title and first post doesn’t seem to be “on-topic” anymore.
Fine of course, as it is Hypnoza’s own topic, just thought I would mention it when someone comes across this topic in the future.
No, it doesn’t matter, even if it’s digital or analog. At one point or another you are summing two tracks, 2 signals, together. If it’s analog, then 2 voltages are summed. So two times 1V (peak or RMS) equals 2V, which is a 6dB rise. If the input of the next device can’t handle 2V, it clips. In the digital world 2 samples are summed. So ie 1111 1111 1111 1111 + 1111 1111 1111 1111 = 1 1111 1111 1111 1110. That result is more than 16 bits, so your sample is saturated and clips. With a floating point mixer this is less of a problem on the mixbus, but on the way out it still can.
Because bass needs the most energy, and thus causes the highest voltage swing, or bit value, it is advised to at least drop the bass frequency from one of 2 tracks. Chances of distortion are then lessened.
On top you need some clarity in your mix. Just as a sound engineer will put high pass filters on everything except kick and bass, and will drop the mids on electric guitar to make room for the vocals, you as a DJ will also have to play with your EQ to let the part of a track you want stand out, preferable by cutting instead of boosting.
It’s simple audio physics, and it will roar its head in DJing, live sound, studio work, cover bands, and even orchestras. Learn to use EQ, keep an eye on the VUs, and keep an ear on the mix. This is the most often forgotten skill in DJing, but back in the day you could ruin speaker systems if you forgot to do it (now everything is superprotected with limiters, but that just keeps you from blowing drivers, not from sounding bad)…