ms compressor

compressing the mids of a stereo signal is a standard operation & it's easy to see why. the principle is not unlike that of multiband dynamics - a strong fundamental in a kick drum would cause the whole drum kit to duck if compression settings are applied unilaterally to its frequency spectrum. sometimes this is desirable (see: sidechain compression), but often times it is "unfair" to affect the dynamics of the hihats because you want to control the kick. in this case, it is appropriate to syphon off the fundamental of the kick & apply the desired strong compression while leaving the volume of the upper band unchanged.

think about how this concept applies to mid-sides - most sounds are very dense in the mids & delicate in the sides & you may not want to penalize the width of your track based on the dominating center. instead, try isolating the channels & controlling the dynamics separately. note that while this rack makes the whole process easier, it does not have gain control & you may need to manually adjust the chain volume if you apply a lot of compression.