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General Asylum General audio topics that don't fit into specific categories. |
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In Reply to: RE: Here's A More Direct Source posted by Dave_K on December 11, 2016 at 05:38:15:
"There is no sampling in FM radio."
Technically debatable. I know how it works. I guess what people say is that if it isn't quantized it isn't sampled. I call that semantics because even the analog stereoplexers chopped up the signal into pieces 1/38,000 th of a second long.
The technique of the modulation BTW used to be called double sideband suppressed carrier.
It still has its limitations. With more modern techniques such as pilot cancelling rather than a notch filter they could do 17 KHz, maybe a tad more, but it simply is not transmitted.
And with all the digital junk they transmit with it they probably simply can't. In fact some older tuners have a problem with all that digital crap and it comes out as noise even on the strongest of signals with more than ample limiting. There are people out there who modify older FM tuners to fix that. I believe, IIRC, the filter goes in the IF strip. I'm thinking but not sure that if you have a wide/narrow IF bandwidth switch, using narrow should eliminate the noise but then you get the increased distortion. Like, take your pick.
In the old days the other subcarrier was SCA, for store cast allocation and FM tuners started having filters for that. It ran at 67 KHz and I think it was frequency modulated. But not by much, the quality was not all that great because it was used for things like Muzak and maybe voice.
Now of course they got more in there. Your car radio reads out the name of the song that is playing, that is something new. And of course that is a source of noise for older tuners. And to tell you what, the newer tuners I have heard do not sound as good. But then many of them are on a circuit board about the size of a USB thumbdrive. theyy run on a new process, I forgot what it is called but somehow one chip does iit all. there is no IF strip, some don't even have anything that looks like a detector alignment. And the same 18 pin chip also does AM.
Now compare that to an old Revox.
I maintain my position that in most cases FM is good for the car, but not for serious listening. If you get a station without all the digital garbage on it maybe, but where do you find that ? And still, the 15 KHz limitation is still there. Most of you wouldn't put up with that in a cassette deck. At least not for hifi use.
" Then the modulator forms sum (L+R) and difference (L-R) signals."
A comparator did that. In a digital stereoplexer it simply switches between the channels. Much cheaper, no phase problems generating the pilot because a simple flip flop (astable mulitvibrator) does that. The system did make it a bit simpler, but better ? I doubt it. Just like the old redbook CDs speced out better than vinyl, sometimes the vinyl just sounds better.
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Follow Ups
- RE: Here's A More Direct Source - JURB 15:22:28 12/11/16 (2)
- RE: Here's A More Direct Source - Dave_K 08:36:53 12/13/16 (0)
- RE: Here's A More Direct Source - JURB 15:32:57 12/11/16 (0)
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