More is better always?
"I have noticed on many stereo systems a switch for "stereo enhance". Flipping this switch does exactly what the name says; the stereo width becomes much wider and sounds much more open and expansive. How does this switch work? Is there a way I can apply it when I'm doing my own mixdowns?"
A stereo signal can be thought of as two main components: the Left + Right component and the Left - Right component. The L + R is a mono signal, as if the left and right are summed together. Anything panned to the center (such as a lead vocal) is found primarily in the L + R component. The L - R component is all of the "difference" information that makes up the stereo part of the signal, basically all of the stuff panned to either side. As a general rule stereo enhancers work by increasing the ratio of L - R material with respect to the L + R material. This is accomplished in a variety of ways depending upon the system, but it is sometimes as simple as summing the stereo signal to mono and then mixing a polarity reversed version of it back into the mix while raising the overall volume to compensate for the lost level. This effectively "turns down" the L + R component relative to the L - R stereo component. The harder something is panned one way or the other the louder it will get relative to things more near the center, which creates the illusion that the stereo field is wider. This is also a rudimentary look at how many vocal eliminators do their trick. Some devices are much more sophisticated than this simple explanation, but they pretty much all accomplish their magic by inserting out-of-phase components of some part(s) of the signal back into the main mix.
This effect can be interesting to use on a mix and you can try it by running your mix through such a stereo and back to your tape deck (or whatever you use), but beware that what may sound cool to you today may sound utterly ridiculous in a few weeks. More stereo is not always better. Playing such tricks with the phase coherency of your material can cause it to sound radically different (usually worse) on other playback systems. It is easy to create a mix that almost completely disappears when played back on a mono system (remember you are reducing the level of the mono L + R component). The effect is often more useful when judiciously applied to one or two tracks of your mix you want to call attention to in this way. There are software plug-ins and lots of hardware boxes that can provide this effect, and many of them will do a much better job than a switch on a stereo. Some have very sophisticated algorithms that manipulate the audio in careful ways so as to minimize unpredictable anomalies playing back the material on other systems.
