[guygee]

I was trying to figure out the significance of the spike at 19KHz. I was wondering if the way that stereo signals transmitted by FM might have something to do with it:

A stereo FM broadcast consists two signals are mixed in such a way that two output signals are produced, one is (L + R) and the other is (L - R). In turn, these two signals are processed to produce FM signals, one at the carrier frequency and the other at the carrier frequency plus 19kHz, that are transmitted from the station. When you tune to the station, de-modulation in your radio receiver recovers the two signals, (L + R) and (L - R). To get the individual L and R channels these two signals are added to produce:

(L + R) + (L - R) => 2L

i.e., the original left signal, and subtracted to produce:

(L + R) - (L - R) => 2R

i.e., the original right signal.

Could the 19KHz spike be an artifact of some problem with the reproduction of an FM stereo signal? I'm really not sure if I am on the right track...I would be interested in anybody else's thoughts on this.