Tonight I visited a meeting with presentations, organized by the Dutch Guild of Multimedia Engineers and the Audio Engineering Society (AES). Most of it covered DAB+ (Digital Audio Broadcast), but there was one brief talk (a much longer one will follow) about FM and loudness.
It turns out that there's one Dutch company that created the FM reception chips that are used in 75% of all car radios sold worldwide. And they are using some very specific tricks to handle bad reception.
Say we want to receive the green (weak) station. As you can see the much stronger (red) stations' RF signal will cause big disturbances.
Solution: Make the 'window' at which we look less wide (the black image). BUT... If the green station is broadcasting a very loud signal with a wide RF image, we cannot make the window smaller because it will cause distortion.
Claim: If the green station would lower its level, reception would be greatly improved, and signal vs. noise (incl. the signal from the other station) could theoretically be improved by upto 40 dB (!).
It kinda seems to make sense. What I don't get though is this: If the effect is THIS big, someone should have noticed it?
yeah my radio does this shit. if the signal goes below 50 db-uv it goes mono. The other interesting stuff is how well it can separate signals. i tested one time with two transmitters on the same freqvency and it switches between them as you would switch between two stations in memory with no impurities or overlaping sounds. if you encrease the modulation past 100 khz it goes to mono automatic and some times even shows decreased receiving signal.