Stereo frequencies
We now know how to assess our mix’s mono compatibility in relation to a ‘pro’ mix. What next? Well, you can now identify exactly what your mix is lacking in stereo, ‘holes’ in your track’s stereo field, and whether vital mix elements are present enough in both mono and stereo in comparison to your reference tracks.
Listen to how the frequency balance of stereo content changes when you sum to mono. If a bright stereo sound (ie, a reverb or delay return) suddenly becomes too dull in the mono mix, use an M/S EQ and add a gentle high-shelf boost to the mono signal, then an identical high-shelf cut to the side signal. Or, use an M/S utility plugin to simply turn down the side by a dB or two, then turn up the mono signal by a corresponding amount to rebalance.
When you listen to the side signal of your mix, listen out for ‘empty’ frequency ranges that can be filled with stereo content. You can visit a sound in the project, then ‘pocket’ some width into that missing frequency range with reverb, short delay, panning or stereoisation.
As discussed in 260’s Next-Level Mastering feature, bass frequencies are non-directional, so the frequency range below 100-200Hz should be kept in mono. However, modern producers often break this rule to a certain extent: the power of a dominating 808 bassline, for example, can be enhanced by pocketing stereo information in the low-mid area between about 150 and 400Hz.