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wrote:

I was wondering how a music signal gets compromised when it is
transmitted via FM radio. Other than squash-it-to-death broadcast
limiters, is there something about FM that reduces signal quality (less
stereo separation, distortion, less bass, less dynamic range).

just wondering what gets compromised and why...

The IF bandwidth in the rx is often limited to around 300Khz which causes
some distortion.

Transmitter audio bandwidth is limited to 15Khz to protect the pilot at 19K.

The Preemp can be a issue if you are driving the transmitter hard, but it IS
possible to have very good sounding FM radio, just not very LOUD at the
same time!

For compatability with mono receivers, the signal is transmitted as L+R in
the 30Hz-15Khz region, with L+R suppressed carrier modulated onto a
subcarrier at 38K. A 19K pilot is used to both signal the presence of a
stereo broadcast and to sync the 38Khz carrier at the rx end.

Now one of the properties of a band limited FM signal in a noisy channel is
that the noise spectrum of the demodulated signal rises with frequency.
Thus the recovered L-R signal has a much worse SNR under weak signal
conditions then the L+R (mono) signal does.

The rx can use this to degrade gracefully under weak signal conditions by
reducing stereo separation to maintain noise performance. This is good
engineering and makes for a more robust system, however if you want to be
heard on car radios (and in fact on mono portables), then you had better
make sure that your signal is mono compatible! Some modern music
(particularly some drum machines) put out out signals which while
essentially mono are inverted between the left and right outputs. Obviously
a mono rx (or one that has degraded to mono due to weak signal) will
completely fail to reproduce this bass.
Dance music producers, this means you need to watch the jellyfish meters!

FM in built up areas suffers from multipath distortion which is its major
weak point, good aerial positioning helps with this, and it is possible to
detect it by looking for ripple on the pilot.

HTH.

Regards, Dan.