SD> use compression... for those in the dark, it's where the radio
SD> station lowers the bass and treble sounds and emphasizes the
SD> midrange so it can sound "louder" at the limited range that sounds
The compression I'm familiar with deals with signal amplitude, not 
frequency. FM stations commonly use compression so that the transmitted 
signal amplitude remains reasonably constant, thereby maximizing the 
range at which the signal can be received acceptably. Observe the signal 
level on your stereo (on the receiver, if it has one, otherwise run 
everything through a tape deck and use its meters) while listening to an 
FM station, a CD, and a tape deck and/or turntable. You'll find that the 
FM station will be virtually the same level pretty much all the time. 
The tape deck or turntable will be next, with some variation, and the CD 
(depending on source material) will have the widest range of levels. 
Analog storage media (tapes and records) had limits on the range of 
signals they could handle. Too low, and the signal was swamped by 
background noise inherent to analog (vinyl surface noise, tape hiss, 
etc.). Too high and the media saturated, distorting the signal. One of 
the most notable improvements offered by CD is the wider dynamic range 
it offers.
Of course, FM stations do also clip the frequency response to remain 
within their allotted channel. Top end is 15 MHz, as I recall. And it 
wouldn't surprise me if the midrange was emphasized, since that's the 
most easily heard part of the spectrum.
kabrams@erols.com
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