[paddington]

He's asking about HD Radio broadcasting. Radio stations in the US (and maybe Canada? not sure if the standard has been adopted yet there) are putting "side channels" on the air that carry the normal programing as well as other, more niched programming. The standard is called IBOC (In-Band, On-Channel) broadcasting and the frq range is 20-20kHz of digital audio. It allows for two extra audio bands for every FM analog signal.

Is is not linear, but is is a much higher quality than FM (which is means it's better than satellite radio, too since XM / Sirius' audio compression is worse than Real Audio was over the internet in 1997...)

I'm thinking we should allow IBOC broadcasts as they are about to become extremely common over the next 15 months (you can get HD-Radio signals in over 100 cities now days) and, though it isn't linear, the quality is high - like DVDs aren't linear, but MPEG2 is considered acceptable.