For Best Results:

Make sure your signal has NO DISTORTION.

Make sure your output levels are not too LOUD.

Check your playback meters to see that they are not constantly on the red.

If using software, output levels should not be over-clipping excessively throughout the mix.

High peaks should be ideally at -0.5 db and lower.

This example shows 3 stereo mix signal levels. Our focus is on levels.

The first signal (1) on the left, peaks at about -11 db which is plenty of headroom for us to apply our mastering magic.

The second signal (2) from the center, peaks at -0.5 db. We can work with it, but for best results peak levels should be between -3 and -6db .

The third signal (3) on the right, peaks at above 0 db and clips the meter. That's not ideal for professional mastering, specially if it's not the peak but the average sum levels (of the L + R channels). We don't recommend you submit mixes like that.