By Dave Crane
Plug-In Power: Separating Mono and Stereo Elements Using Mid-Side Techniques
In past articles, we’ve talked about the benefits of Mid-Side recording, as well as the physics behind it. But did you know that you can apply the same principles to mastering a stereo file (also know as “program material”)? You may have a track that cannot be remixed and has a vocal (or some other mono element) that is too loud or too soft. Or all the mono components of a mix are too loud, and you want to bring up the stereo elements like the reverb. The way Mid-Side mastering achieves this is to separate the mono elements from the stereo elements of your mix. This then allows you to change the gain and EQ, or to compress the mono or stereo elements separately.
The stereo file goes through a process called Mid-Side encoding. This can be done in some DAWs via the mixer and phase reverse switches, although I had the best luck in Pro Tools and Samplitude. The encoding separates the mono and stereo elements onto different tracks, which can then be adjusted relative to each other. Then they are fed to another set of aux tracks and “decoded” back into a stereo file. There are dedicated mastering hardware boxes and consoles for this, and some DAWs offer easy ways to do this as well.
To isolate the mono element of a mix, combine both channels together into a mono file. Mathematically, the Mid signal is represented by M = L+R/2. To isolate the stereo element of a mix, combine the left channel with a right channel, but flip the phase of the right channel 180º. Doing this removes the elements of the stereo field that are common between the two channels (which would be the mono signal), leaving only the stereo portion of the signal. Mathematically, the Side signal is represented by S = L-R/2.
Did you know that you can apply the same [mid-side recording] principles to mastering a stereo file?
You might be wondering what the “/2” means. It simply means “divided by two,” because when you sum the left and right tracks, the result will be louder. Rather than get into more mathematics, once you have the Mid and Side tracks isolated, you’ll need to decrease them by 6 dB each. This will ensure that they will not clip, and that the result will have the same amplitude as the original stereo track.
You’ll need to decode your M-S stereo track back into a stereo track to monitor it. You can do this with three aux tracks in a DAW. First, send the Mid signal to Aux 1 and pan it center. Then send the Side signal to Aux 2 and pan that far left. Then send the Side signal again to Aux 3 with the polarity reversed and pan it far right.
Once the mono and stereo tracks are separated, they can be compressed and/or EQ’d separately. For example, let’s say the cymbals sounds dull on a stereo program track you’re mastering. If the cymbals were recorded in stereo, you can run the program track through a Mid-Side encoder, and then just apply some "air" with the Precision EQ to the Side signal. Or, you can compress the Mid signal if the mono elements in the mix seem to have too much dynamic range. You can even use a the Precision Multiband compressor on the Mid signal to compress the kick, for example, without affecting the vocal.
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UAD Precision Equalizer |
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UAD Precision Multiband Compressor |
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UAD Fairchild 670 Compressor |
The Fairchild 670 can actually function as a Mid-Side compressor. Most people don’t know this, even those who have messed around with the Mid-Side elements (usually to achieve a spacey effect). Try loading the preset “Lat Vert,” and play a stereo piano, or some other dynamic, dual-miked stereo track though it. It almost makes you dizzy.
But you can use this mode of the Fairchild to achieve Mid-Side compression. In Lat Vert mode, the Fairchild compresses the Mid (mono) and Side (stereo) signals separately,A either bringing out or reducing the mono or stereo elements of stereo tracks.
In the videos below, I demonstrate using the Fairchild 670 plug-in to compress the mono and stereo elements separately in the mix. I suggest you listen to the example with headphones, or with high-quality monitors placed in the correct monitoring position to get the full effect. While this example is somewhat extreme for a mastering job, mastering tweaks like this tend to be subtle, so good monitoring is essential. Also, be sure to download the presets and try them on your own tracks.
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| Download the Presets | |||
If you’re in a hurry, you can watch the movie on our Universal Audio You Tube Channel.