mid-sides processing is a powerful (if at times underused) tool. it primarily allows you to widen or narrow the width of stereo sounds, but it also can function as a kind of multidimensional dry/wet that makes it possible to be at once generous with the application of an effect while still maintaining subtlety. in other words, have your cake & eat it too. if you're not totally familiar with the concept of M/S vs L/R, we put together this video to demonstrate what these terms mean both visually & sonically:

 
 

these ableton racks are designed to provide you with simple tools to affect the mid & sides of your sounds separately in various ways. below you'll find an explanation of each rack, its possible uses, & an associated audio demo (recorded by evan of MAZ Blanko). each rack will turn on about halfway through the sample to give you an idea of its properties.

download here
 

 
 

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.

 
 
 
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ms eq shelves

high passing the sides is a standard technique for cleaning up stereo sounds as low frequency content risks phase issues & is better off being solidly centered anyway. shelves for highs & lows for both sides & mids make it extremely easy to dial in the exact settings you're looking for without any of the fuss of fandangling the eq device. I find this rack particularly useful & I think you will too.

 
 
 
 

ms saturation

similar in idea to eq shelving, saturating the mids will bring more fullness while preserving the air of the sides, while saturating the sides works as a widening technique to give them more presence. all the while, you'll find you can be much more generous with the effect & wallow in its transparency. 

 
 
 
 

ms delay

ms delay is a little more unusual, but the idea is the same as all the other racks - effects need not overwhelm your sounds. sides are often associated with ambience, so you could use this rack's included  delay & reverb to experiment with widening sounds by increasing the "atmosphere" in the side channel.

 
 
 
 

ms utility

just a utility, but every bit as useful as any of the other racks. sometimes all you need to widen your sounds is to add a little gain to the sides, sometimes you need to flip the phase to make your sounds jive, & sometimes you need to pan to get them out of one another's way. with the mids & sides isolated, these standard operations can become very interesting, but don't expect everything this can do to be particularly suitable to your track (especially the phase options).

 
 
 
 

so that's it - hope you find these useful! they should either speed up your workflow or encourage you to use more advanced processing techniques. again, download here.