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Post by Druid Hills Radio on Apr 19, 2017 14:20:03 GMT
FM Stereo is 56 Years Old Today!  |
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Post by Boomer on Apr 19, 2017 20:24:06 GMT
Maybe that's why I've been seeing more articles about FM radio.
I read in two separate places that a noisy system was implemented to give stereo to FM, and people believe it was a technical error at the time. That would be using double side band, an AM mode, for the stereo information, leading to high levels of noise, especially under weaker signal conditions.
I wonder what other form the stereo information could have taken that wouldn't cause the noise penalty?
Boomer
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Post by thelegacy on May 8, 2017 14:30:42 GMT
The only other form would have been the Harris format that CKLW experimented with and we had heard that on Youtube. That would have been an AM type format but with a sort of PCM coded Stereo I think.
Some people swear they can hear the 19 Khz pilot signal used to tell the receiver that there is a Stereo signal. I know we hear it as a hiss but some say they hear a sort of high pitched whistle in the background of an FM signal.
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Post by mark on May 8, 2017 15:44:25 GMT
According to experts, especially HI-FI experts, humans can hear from 20HZ to 20KLZ.
But according to audiologists that's only if you are under 25 years old.
They will tell you that the HI-FI experts are wrong and in music nothing is up there anyways that you would hear.
Audiologists have gone to school to study this so I will take what they say as true.
As for the 19klz tone a kid or maybe a teenager could hear it if loud enough.
But taking into consideration the curve of human hearing which is most acute between 500 and 5000 HZ, and at low volumes especially, drops off sharply at below 200HZ and above 10KLZ(A weighting on a sound level meter) so hearing 19KLZ at normal listening volume is not likely.
But the 15KLZ from the TV oscillator I remember I could hear when my head was at a certain angle when I was younger.
Mark
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Post by Boomer on May 9, 2017 1:19:37 GMT
From what I know, all of the working AM stereo systems use phase modulation, so that's probably what you heard about Harris, Legacy. The AM signal is sent out like any AM station, and it's both left and right channels combined, the stereo information is sent through phase modulation of the carrier, which the normal radio ignores, but the stereo AM radio uses the phase information to reconstruct the original stereo audio.
Have you gotten into SDR, software defined radio yet? I saw a demo video using the Funcube USB dongle on a Windows computer, picking up a stereo transmitter with perfect reception.
As for high frequencies, The Beatles recorded a tone on Sgt. Pepper's Lonely Hearts Club band after A Day In The Life, I think it was 15 khz, and designed for Dogs to hear, possibly for Paul's Sheepdog, Martha at the time (She looked like my icon). I think that's how the story goes, I've heard it for years.
When I came home from school, I could tell when mom had the living room TV on by the squeal, when I was standing outside the door. Since TVs have gone to flat screens I don't know if I'd still hear it. I hear 10 khz whistles on AM radio from adjacent channels though, on better receivers.
Boomer
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Post by Deleted on May 9, 2017 11:38:19 GMT
The Birthday of Stereo and Good Hearing
Mark looks into the ears: "According to experts, especially HI-FI experts, humans can hear from 20HZ to 20KLZ.
But according to audiologists that's only if you are under 25 years old.
They will tell you that the HI-FI experts are wrong and in music nothing is up there anyways that you would hear.
Audiologists have gone to school to study this so I will take what they say as true.
As for the 19klz tone a kid or maybe a teenager could hear it if loud enough.
But taking into consideration the curve of human hearing which is most acute between 500 and 5000 HZ, and at low volumes especially, drops off sharply at below 200HZ and above 10KLZ(A weighting on a sound level meter) so hearing 19KLZ at normal listening volume is not likely.
But the 15KLZ from the TV oscillator I remember I could hear when my head was at a certain angle when I was younger."
Learning about ears is very interesting territory.
A girlfriend of mine says she can hear radar. That seems impossible, but in a book I have called The Zapping of America, mainly about the health effects of electromagnetic radiation, there is a section about how some radar operators in the military have claimed they could "hear" radar. Sometime I will look that up and quote it directly.
I have also been surprised to learn that more people than we would think suffer from hearing impairments that may be going untreated. This has a huge effect on whether they like music or not, because to some of them music sounds irritating. In some cases all they need is to have their ears professionally cleaned of junk that's blocking the ear canals. I think exposure to loud sound has damaged a lot of people's hearing.
Ordinary things like operating power lawn equipment can damage hearing if ear plugs aren't used.
Super loud ear-buds and head-phones can cause damage.
Rock concerts so often have the deciBel levels of a military attack.
Free hearing tests at the next ALPB meeting.
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Post by thelegacy on May 10, 2017 16:39:20 GMT
I can remember using a tone generator to test the frequency response of a cassette recorder. If the meter falls after a certain frequency that was where the response began to fall off. The JVC's did quite nicely. I could get to 20Khz and still have the same reading.
It also worked when comparing the different brands of tape. When comparing a Cro2 tape to a metal one. I bring this up because I should be able to tell the frequency response of a transmitter as well if I was to once again obtain a tone generator.
In science class we put beans on top of the speaker and did a slow tone sweep. At a certain frequency those beans would pop up so high it was funny to do it.
The things I thought of after I read this.
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Post by Deleted on May 10, 2017 16:48:52 GMT
Jumping Beans As a Speaker Test
Absolutely, TheLegacy...
A tone generator can reveal the frequency response curve of a transmitter, but you would be viewing the audio meter off of a radio, which would confuse the result, because the frequency response of the radio would be part of the result.
Maybe there's a way to get a pure audio response reading from a transmitter, but I don't know.
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