Stereo Tool

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?

As you say Hans, is interesting, but also something strange.
In FM always preached that the signal processing while maintaining a high level audio noise ratio improvement. And this improves the range and reception of a station. Now it comes with something that promises too many dB's advantage, and no one has noticed this?

I have not read anything about this, if you have a link I spend? I'd like to read something that explains a little more about it.

Thanks for the news!

_________________
by GAP
"Less is More" (Bob Katz)

Are we talking about IF filters here?

I know that some car radio receivers reduce side signal in M/S (partial "monoize") when RF reception is weaker.. so that is a kind of "reducing bandwidth". At the edge of coverage, it switches to mono, so no MPX signal is demodulated anymore..

I indeed have a problem with the fact that no-one would have noticed this. The claim is that what happens is not so much mono blending, but actually making the reception filters steeper. Which would indeed remove a lot of noise coming from nearby stations.

Without that, putting more sound in the same bandwidth should indeed improve signal/noise ratio (where I put any disruptions from other stations under noise).

I suspect what the guy says is true, but...

Not a great idea. If everybody decreased their deviation, it wouldn't sound as distorted on narrow banded receivers, but what do you gain? Nothing. Most listeners get a crappy signal and a few people on the fringe get a slight improvement in interference. It would only work if everybody did it and that would take government action. Maybe he gets to sell a few more receivers...

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.

if some of you have VAG (vw,skoda,seat) newer vehicles try keeping the setup or sound button for longer then 5 seconds and you will enter diagnostig menu of the fm receiver and you will see a lot of details.

Capture effect maybe?