I thought this reponse to the original question here might be of interest. This response was received from John Wood at Inovonics and it explains the process very well.
> The 222 does not create asymmetry, nor should any processor. If it
> does, it is, by definition, introducing 2nd harmonic distortion. Any
> sound, save a pure sine-wave tone, is generally asymmetrical... a
> trumpet note, the human voice, even a 'blended' orchestra. The 222
> simply allows naturally-occurring positive-going program peaks to
> assume a value up to 125% of the negative ones, as allowed by the FCC
> in AM broadcasting practice. The advantage, in terms of a perceived
> loudness increase, depends somewhat on the asymmetrical source, but
> it's on the order of 1dB. Big deal, eh?
Full Thread Here: http://www.broadcastengineering.info/viewtopic.php?t=2585
Thanks John WDCX for setting straight what is and has been, I agree, a continuing misunderstanding about what the 222 actually does.
Amid your explanation is the (also) little realized fact that acoustic musical instruments as well as the human voice naturally produce asymetrical sounds, which I believe is where computer synthesized music comes short on quality because computer DSP audio chips produce symetrical sound waves which are not easy on the ear.
In regard to digital recordings taken from live acoustic performance, I'm not sure how much of the natural asymetry is retained, but it is an important companion issue alongside the 222 topic.
ANY improvement to a miniscule Part 15 signal is better than nothing (1 db corresponds to about a 25% power increase). I do have a 222, and found that it made a noticeable difference, particularly in my fringe range (that is, the area in which I could hear my signal with noticeable noise).