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FM Radio transmitters broadcast a continuous 19 KHz pilot tone to indicate that it's a stereo broadcast. If it's present, then there's also a 38 KHz AM modulat
by CliffStoll 2y ago
FM Radio transmitters broadcast a continuous 19 KHz pilot tone to indicate that it's a stereo broadcast. If it's present, then there's also a 38 KHz AM modulated carrier, which has the stereo information.
The main FM modulation is (Left + Right) audio channels - the baseband. The 38 KHz subcarrier is (Left - Right). Notice that the stereo information is likely to be higher noise, being AM and without a lot of power. So on weak FM broadcast signals, you're often better off setting your tuner to mono.
Some cruddy FM tuners don't properly filter out the 19Khz pilot tone, resulting in ear-ringing in the listener.
- LeoPanthera 2y agoThe unfiltered pilot tone was a problem when recording FM radio onto tape, beating against the bias tone and confusing Dolby NR into thinking there was constant sound. High-end cassette decks had an "MPX Filter" which was a sharp 19kHz filter before the recording system.
- CliffStoll 2y agoYou betcha! And FM broadcasts have a high-frequency pre-emphasis, which adds something like 10dB of boost to audio high frequencies. This is to reduce high frequency noise that occurs in analog FM systems. Radio receivers have a matching de-emphasis high-frequency cut. Indeed, both vinyl phonographs and audio tape systems employ similar pre-emphasis and de-emphasis. It's the RIAA curve for phonographs. Not sure what the standard is for mag tape.
- bux93 2y agoFor mag tape, it's different Dolby NR schemes.
- egorfine 2y ago> confusing Dolby NR Accidental DRM even before the "D" came to be.