Mid- Side Processing Techniques
Splitting sound into Mid and Side (M/S) channels is a very effective method for processing the image and width of your productions. The Mid channel essentially being the mono and centered information, while the Sides represent the edges of a stereo sound. We can use this type of processing to increase the perceived width of our productions, or even redefine the center image. Most commonly found in (but not limited to) EQ plugins, M/S processing can be used for some very effective and creative mixing techniques.
Mono the Low
A very common mixing technique when using M/S processing is to sweep away any side information from your main low-frequency elements. Dealing with some kick drums or bass sounds, you may not want to collapse the whole sound to mono, for instance, your kick drum sample is layered with a hi-hat that has some stereo width you want to keep, or you’re working with a bass that has strong low and mid range elements. Using an M/S EQ, you could sweep away the low frequency from the Sides only, redefining the low end in your sound.
Another one of the most common applications of M/S processing is to boost the top end of your Sides. Using your M/S EQ, apply a high shelf to boost high frequencies on the Sides only. This gives the impression of a bright and wide sound, and works great with leads, pads, white noise and spot FX, and is also a common technique used in mastering for a bright and wide sounding master.
In contrast to the previous technique, an excessively spread sound can sometimes be a little overbearing in a mix. Using M/S processing, we can bring the focus back into overly wide sounds. Sometimes something as simple as Voxengo’s MSED is perfect for this technique, as it features a MID GAIN and SIDE GAIN, so we can simply turn down the Sides slightly, and if necessary apply a small boost to the Mids.
Centering the sub frequencies with Mid processing, or pushing mid/high frequencies out wide with some Side processing, are both effective ways to deal with some bass and lead sounds. However, this can sometimes lead to a lack of warmth or weaken the signal. If you experience this problem, try using some Mid processing on the lower mids to bring some definition back into sounds. Try boosting the Mid EQ just after where your kick drum is peaking, to provide some nice separation and clarity with your low-frequency elements.
Bus Send M/S Processing
A nice trick for clean and wide reverb sends is to apply an M/S EQ after the reverb effect on your bus channel. While a normal EQ plugin can cut a muddy low end from a reverb, sweeping too much away can leave an unnaturally thin sounding effect. Using M/S EQ here, we can cut the mud away from the Side channel only, by sweeping away the low end and dipping some of the low mids, while retaining those frequencies on the Mid channel. We can always boost some lower mids back on the Mid channel if the effect sounds unbalanced. Simultaneously, we can boost some high frequencies on the Side channel, for a wide and spacious reverb.
Try automating some M/S processing to draw attention to the main sections of a track. Working with a vocal, you could automate out the Sides of your lead for chorus or drop sections, to give a big wide sound for those highlight moments. Or you could try some M/S EQ automation to deal with frequency masking, for example, you have a big wide lead sound and when your introduce your pads the two sounds fight for attention in the higher mids. Set up some Side processing on one sound to dip the high frequencies when the other sound plays, to simplify this process set up the M/S EQ and automate the on/off for the plug in.
M/S processing isn’t limited to your EQ plugins; some compressors are capable of processing the Mid and Side channels independently. A hugely powerful mixing tool, you could compress your Mids to push them back in a mix, giving a wider effect, or equally, compress the Sides for a more defined and centered sound. You could even use your M/S compressor as a sidechain, ducking only the mid and low frequencies on your lead when the kick sounds, provided your kick is centered it’s these frequencies in the Mid channel where they’ll be fighting for space. Or try using some M/S sidechain compression to duck the sides on your lead when your vocal sounds, to give the vocal more space and presence.
For a different technique, try some M/S processing using an exciter. This will give a similar effect as when EQ’ing, however, an exciter will process frequencies slightly differently, adding a pleasant saturation. Try exciting the Sides of the 10k and above region on your drum group or master, adding some wide air and crispness to your mix. Likewise, try exciting the low end of your mid channel for a warmer and deeper sound.
Some distortion plugins can operate in M/S mode, which leads a whole realm of creative possibilities. One technique would be to distort your sides signals quite heavily, leaving the Mid channel untouched, adding some crunchy width. Or, add some subtle saturation to your low-mid range on the Mid channel for a warm center.
To apply M/S processing using any plugin you can think of, you could completely split your signal into two channels. Using something like Voxengo’s MSED, duplicate your part and mute the Mid on one and the Side on the other. You could also use an EQ, sweeping away all the Sides on one channel and the Mid on the other. Now you have separate Mid and Side channels for your part, so you could apply a chorus plugin to the Side only, or add some transient shaping to the Mid channel only.