Dual mono versus stereo compression

Should I compress the dual mono or the stereo way? Really, what kind of compression should you use on a stereo source? Like for example when you put the compressor across the master bus, so you can compress the whole mix? Well, my friend, it depends, as usual.

Duality – why compression envelope matters

In the case of the stereo compressor, the envelope of the gain reduction will be the same in both the left and the right channels. It’s because – depending on the unit – the key signal will be either the sum of both side signals, or the loudest side of the two will be the one triggering the compressor. It’s all cool and dandy, as long as you don’t mind that it will make the resulting stereo sound a bit narrower than it originally was. Why? Because the compressor will not listen to the two channels separately. If the louder side gets compressed by a certain amount, the other, quieter side will receive the same amount of compression. That way, it will try to sort of bring the level of the two channels closer to each other, eliminating their differences somewhat. It also means that your true stereo elements, or mono elements that are not hard panned to one side or in the center, will be perceived like they have been moved towards the center.

Now if we use a dual mono compressor, the gain reduction envelopes will be different, because the two channels are independent from each other. In this case, the left and right side signals trigger their own channels. That sounds awesome, right? Your stereo and soft panned (somewhere else than center, hard left or hard right) elements will stay where they are, and you’ll have a nice wide stereo sound, right? Well, not quite. The center in a stereo sound system is an imaginary thing. We only have left and right, so the center doesn’t really exist, it gets created by the signals on the two sides. Why is that a problem, you may ask. It’s because if you put that nice, powerful lead vocal in the center, and a loud and rather obnoxious electric guitar starts riffing on the left side like there’s no tomorrow, well, the left side will get compressed harder… and that will compress the left side of your lead vocal track just as hard! Only the left side of it. So the sucker will be moved to the right somewhat.

So in this battle between stereo and dual mono, it really depends on what you want to avoid: the above mentioned center drift or some shrinkage of the stereo width. Many compressors come with both functions available. It’s good cause you can freely decide between both the stereo or dual mono operation. This way you can pick the optimal, best sounding kind of compression. These units can be used either the dual mono way, or with linking the two channels, they can be used as stereo compressors. In the plug-in world, you can download the newly released ThrillseekerVBL for free, that can operate both ways as well.

So, should I go with dual mono or use stereo compression? Make artistic decisions and choose the one you like the best!