If your mixes and tracks sound poor quality, this might be why. We get sent a lot of tracks and mixes that have this problem, but there is a very simple solution to avoid it in future.
This applies to recording (DJ mixes, vocals, instruments) and producing. If your volume goes above 0db it can distort which will ruin the quality of your sound. All you need to do is turn your volumes down a little so that nothing goes above 0bd. You should have a volume meter / indicator on your recording software that will show you if your levels are too high. You can also do a test recording and look at the waveform to see if there is enough headroom (see image below).
As you can see in the top image there is no space at all and the sound has gone over 0db so can sound harsh and fuzzy in places.
The 2nd image shows audio that has been recorded at a lower volume so has plenty of space and nothing exceeds 0db. This audio will have no distortion and sound much cleaner.
Of course, if you record at lower volume your audio will be quieter but when you have finished recording you can 'Normalize' your audio to get it back to full volume (one click of a button in most recording software), or get it mastered by a professional.
Its easy to make a recording louder if it it has been recorded at low volume. It's not easy to remove distortion if you have recorded too loud.