No one has "good" hearing above 16kHz; at least no one over the age of 10 or so. And if one has spent a lot of time listening to portable stereos through earbuds, turned up suitably above the ambient din - or worse, modern car stereos, commonly used (with pop, rock, metal, punk, rap and hip-hop) at sound pressure levels in excess of 120dB - their hearing is likely not very good at all above 12 kHz if they are age 20 or older.

Audiologists have been noting for some time that premature hearing loss is getting to be a widespread medical and social problem, at least in "advanced" countries, where large numbers of young people can afford these toys.

It is more likely that it is sub-harmonics (a nasty form of intermodulation distortion) of this ringing that are being heard, not actual frequencies above 16 kHz. In other words, while the frequency traces in Adobe Audition (nee Cooledit) may show ringing at over 16 kHz, I doubt very much that that is what people are actually hearing.

That being said, even if one cannot hear significantly above 16kHz, these frequencies can and do influence how one perceives sound. Research has shown that ultra-sonic information even up to 40kHz or so interacts with the frequency band we can hear, helping to convey the subtle spatial cues that high-end audio freaks (especially the die-hard analog Nazis) call "imaging."

That is why I "just say no" to any bit rate, with any codec, lower than 192kbs. With classical music and jazz anyway, I can often hear artifacts - usually subtle, but always annoying - below that rate. Violins can acquire a steely edge, cymbals acquire a "tearing paper" quality, brass become hard and glassy.

The problem is that I often play my encoded material through my good rig at home, and issues that are inaudible through an iPod - even with good phones - in the typical noisy coffee shop environment, are bothersome through good amplification and speakers in a quiet home setting.