PreSonus Blog

The post on using mid-side processing with the CTC-1 garnered a good response, so let’s follow up with one of my favorite mid-side techniques: M-S reverb.

To recap, mid-side processing separates sounds in the center of a stereo file from sounds panned to the sides, processes them individually, then puts them back together again into stereo. It isn’t a perfect separation, because the mid is the sum of the left and right channels. Although this boosts the center somewhat, the mid still includes the sides. However, the side channel is quite precise, because it’s derived from putting the right and left channels out of phase—so the center cancels.

Applying Mid-Side Reverb

Before getting into how to make M-S reverb, here’s why it’s useful. Some productions have an overall reverb to provide ambiance, and a second reverb (often plate) dedicated to the vocal. The vocal is usually mixed to center, so it’s competing for space with the bass, snare, and kick. If they’re contributing to the overall reverb, and the vocal is creating its own reverb, that’s a lot of reverb in the center.

One popular fix is adding a highpass filter prior to the overall reverb, set to around 300 Hz. This keeps the bass and kick from muddying the reverb. However, it doesn’t take care of midrange or high-frequency sounds that are panned to center, like snare. These can compete even more with the vocal if they’re in the same frequency range.

While some reverbs let you tailor high- and low-frequency reverb times with a crossover, this doesn’t cover all the processing you might want to do, nor does Studio One’s Room Reverb include these parameters. Mid-side reverb, with different reverbs on the mid and sides, is a more flexible solution for customizing an overall reverb ambiance.

Assembling the Mid-Side Reverb

Download the FX Chain, or if you want to roll your own, start by dragging the MS-Transform FX Chain into a bus (of course, this also works for individual channels). Then drag a Room Reverb into each split (Fig. 1). The default reverb preset is a good place to start, but if the FX Chain is in a bus, remember to set the Mix controls for 100% wet sound. I also like to insert a Binaural Pan after the second MixTool to widen the overall stereo image.

Figure 1: Mid-Side Reverb FX Chain, which adds two Room Reverbs and a Binaural Pan to the MS-Transform FX Chain.

The reverb on the left handles the center, while the reverb on the right processes the sides. Lower the fader after the left reverb; Fig. 1 shows -6 dB, but adjust to taste. This alone will open up some space in the center for your vocal and its reverb. However, where this effect really comes into its own is when you tweak the reverb parameters for each reverb. For example…

• If you still want reverb on the kick and low end, vary the mid reverb’s Length parameter. Shorter lengths tighten the kick more, while longer lengths give that Kick of Doom reverb sound.
• Increase Length on the sides for a more atmospheric reverb sound.
• Increase pre-delay on the sides, to make space for attacks on the vocal track. Consonants benefit from the extra clarity.
• For this application, Eco mode sounds fine but try HQ as well.
• Turn up the Binaural Pan after the second Mixtool. I often turn it up all the way, because it sounds great in stereo, and there aren’t any phasey issues of the output collapses to mono.

By adjusting the two reverbs, you can sculpt them to give the desired overall reverb sound. If you then place a vocal in the center with a sweet plate, I think you’ll find that the vocal and overall reverb create a smooth, differentiated, and conflict-free reverb effect.