As with many mix processes, though, a common challenge is to achieve sufficient width enhancement without incurring unwanted side-effects. For example, using stereo reverb for widening purposes can distance the vocal; stereo modulation and pitch-shift treatments can easily sound artificial and/or dated; and hard-panned delays can introduce catastrophic mono-compatibility problems.
Within this context, what impresses me most about Nugen Audio's Stereoizer Elements is its negligible processing side-effects. First of all, it only distances the vocal very slightly. It's more like it helps the vocal glue itself to the track, which I actually consider an advantage. (It's something I actively look for in a widening effect, in fact.) Also, it's very difficult to get Stereoizer Elements to sound unnatural — even at its strongest setting the main side-effect seems to be a bit of midrange tonal emphasis, which is relatively easy to compensate for using EQ if it bothers you. And as for mono compatibility, that's exceptionally good: bypass the plug-in with your mono button down and the sonic difference is negligible.
Despite Stereoizer Elements working so well 'out of the box', I do nonetheless have a few tips to help you get the best out of it. The first thing to say is that this plug-in is designed to be used as an insert effect. If you try to use it in a send-return configuration, the dry signal it passes will effectively mess with your dry signal's mix balance as you adjust your effects-send level. Secondly, it's important to realise that, by its very nature, the Stereoizer Elements algorithm will make the processed sound appear louder in stereo, because it adds level to the stereo signal's Sides component while maintaining the level of the Middle component. So when you're toggling the plug-in's bypass button to evaluate the appropriateness of its settings for your mix, do make sure to take advantage of the Trim control to match the subjective loudness of the processed and unprocessed sounds. If you don't, you're likely to overprocess, because a louder signal will almost always sound subjectively 'better', regardless of whether it really is!
Be sure to balance the subjective levels of the processed and unprocessed signals using the plug-in's Trim control to steer clear of loudness bias when evaluating your stereo-widening settings.
Finally, don't restrict your use of Stereoizer Elements just to the main tracks in your mix, because it's also great for inserting into effects returns to adjust the width of modulation, delay, and reverb treatments. This is particularly useful where you want to incorporate vintage-style mono devices such as spring/plate reverbs, guitar-pedal delays, or tape echoes into a modern stereo mix presentation. What's more, you'll find that you can usually crank up the width enhancement all the way under those circumstances without any tonal concerns, simply because the effect will inherently be more recessed in the mix. And don't forget that you can also narrow over-wide effects using negative Width values, as well as rebalancing off-centre reverbs by dragging the little Balance arrow at the top of the main Analysis display.
The stereo Balance control above the plug-in's main Analysis display can help centre lop-sided reverb effects.