Dolby FM D-Emphasis
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steerpike2
Super Member
'Normal ' deemphasis in the US is 75uS, in Europe 50uS.
Dolby deemphasis is 25uS.
I don't think any Dolby encoded broadcasts exist anywhere anymore; on a normal broadcast 25us deemphasis will distort the treble response, so ought to be left in the 'normal' or 'off' position. Unless you LIKE the odd sound. It will do no harm - except to sanity.
Dolby deemphasis is 25uS.
I don't think any Dolby encoded broadcasts exist anywhere anymore; on a normal broadcast 25us deemphasis will distort the treble response, so ought to be left in the 'normal' or 'off' position. Unless you LIKE the odd sound. It will do no harm - except to sanity.
What measurement is "uS"?
mhardy6647
Lunatic Member
it's meant to represent microseconds... it's the time constant of the de-emphasis filter.
It should, technically, be μs or μsec. "S" is the SI abbreviation for "Siemens", the unit of conductivity.
It should, technically, be μs or μsec. "S" is the SI abbreviation for "Siemens", the unit of conductivity.
Thanks! :thmbsp:
Old_Tech
Yer-isn't!
I will check tonight but I am sure the best sound is with it off or button out. One of the positions has rich full sound and the other has high treble and a noisy background. Sorry I cannot remember which it is though. Pretty sure off is where its set at. If they are not broadcasting in Dolby Stereo, what has replaced that technology if anything? And why is the switch having an affect at all of the encoding is not there anymore?
Thanks for the .EDU :yes:
Thanks for the .EDU :yes:
mhardy6647
Lunatic Member
It is, in effect, a tone control.
Nothing replaced "Dolby FM" technology. It just went away (it never caught on).
Nothing replaced "Dolby FM" technology. It just went away (it never caught on).
jhoyt
Incomprehensible space llama
The Dolby system, whether for tape or for FM worked to reduce high-frequency noise and hiss, and extend HF range, by preemphasising high frequencies on one end, and deemphasising the same frequencies on the other end. The net effect (in theory) would be a flat frequency response, with a much lower noise floor. So as mhardy said, it is nothing more than a tone filter.
AnalogDigit
Realistic fan.
High treble is when the D-Emphasis is on. It is supposed to work if the station is broadcasting in Dolby FM. Some cassette decks in the late 70's had a Dolby FM switch that would decode the station. It was supposed to boost the dynamic range of FM broadcasts. I remember only one station in the Chicago area broadcasting in Dolby. It was FM100 which broadcast elevator music. :thumbsdn: Why that station, I don't know! It died out suddenly because it never caught on. Nothing never replaced it.
steerpike2
Super Member
Does this Sansui actually have the Dolby decoder installed? It may have been a retro-fittable option, as with some other brands.
Old_Tech
Yer-isn't!
I don't think so
I cannot find the double D emblem or mention of Dolby labs on the unit. De-Emphasis is off on my G-6000 unit for rich sound. If it is engaged it sounds tinny. Come to think of it I really never remember there being "Dolby broadcast" stations where I live. When I started seeing the emblem on receivers I thought it was something the stations were already using. Not so I guess it did not catch on. It probably cost a fortune to implement and radio stations being cheap to start with never invested in it.
I cannot find the double D emblem or mention of Dolby labs on the unit. De-Emphasis is off on my G-6000 unit for rich sound. If it is engaged it sounds tinny. Come to think of it I really never remember there being "Dolby broadcast" stations where I live. When I started seeing the emblem on receivers I thought it was something the stations were already using. Not so I guess it did not catch on. It probably cost a fortune to implement and radio stations being cheap to start with never invested in it.
Why Dolby FM failed
Just in case anyone cares....
From an engineer on arclist discussion "FM reception way back when"
"Stereo FM signal to noise was not very good because of the issues mentioned. In the early 1970s Dolby came on the scene with their noise reduction systems. These were used in studio audio, consumer B formats, and Dolby film improvements. Dolby also wanted to improve FM stereo and came out with their model 334 Dolby B FM encoder to clean up FM stereo noise issues.
I was involved in getting the first NPR FM station converted over to Dolby B FM. When everything was done right it worked very well. We measured about 94 DB SN in Stereo and 104 DB SN in mono FM. Rather impressive improved performance, which could be made even better if one later switched over to the newer and better Dolby C and Dolby S systems, that would have made the SN about 10 DB better.
Dolby FM failed in the marketplace and the Dolby FM 334 system had to be taken out. Why the failure? On the transmission side, there was more audible noise found in the Modulator, STL Link, Audio Console, and music program sources that compromised Dolby FM performance as the Dolby would show up their noise shortcomings. Many stations would not change their other equipment or level practices, but had to engage in the loudness wars to keep listeners.
The Dolby FM Encoder also changed the transmitter pre-emphasis from 75 microseconds down to 25 microseconds which technically was a good improvement to allow more high level high frequency signals without over modulation violations. But FM receivers also needed a switch to change their de-emphasis back and forth from 75 microseconds for non Dolby stations to 25 microseconds for Dolby Stations. One also had to line up signal levels to Dolby standards and have a Dolby B decoder at the audio line output of the tuner or the receiver. All this was all just too much for the general public. Listeners did not usually hear programs of master tapes of wide range classical music. Their taste was for other music types with little dynamic range. Most did not have wide range hi-fi stereo systems either, but instead listened on car radios and table top radios. Dolby FM sounded worse to them with its lower modulation levels and changed pre-emphasis. It sounded duller to them as a result. There were no radio or tuners that would automatically and simultaneously do three things.
1. Change the De-emphasis between 75 and 25 microseconds.
2. Turn the Dolby B decoder on and off, and
3. align the signal levels for proper tracking of the tuner's Dolby decoder to the Dolby FM station.
When tuning to a non dolby station, the above had to revert to the old standard FM settings. Many listeners also thought loud was good and powerful. Some did have reception problems that chronic high modulation levels and various processing helped solve.
Thus Dolby B FM stations lost listeners with Dolby B FM, so they pulled the plug on it. Accordingly, it is hard to actually improve FM on air broadcasting unless one can address and fix all issues at the same time in a systematic way. The marketplace, bad technical compromises, government, and consumers were just not willing to do what it took to make things better for the long term good of FM Broadcasting in a comprehensive rational orderly way. A familiar story.
Anyone want to go back to Crosby stereo or Dolby B or Dolby S FM today? With new low noise quiet analog and digital radio station program sources it would sound fantastic, but no one will fight all the battles to do the job right as it must be done. Adding Surround Sound would cause other headaches and problems.
So over the air FM is, by its market place, standards, technicalities, and FCC rules, limited and stuck where it is as to its sonic performance. Satellite, cable, fiber, internet, etc get around FM broadcast's old obsolete standards and limitations, so they largely take the market.
Hope this helps you. Charlie Richardson"
Just in case anyone cares....
From an engineer on arclist discussion "FM reception way back when"
"Stereo FM signal to noise was not very good because of the issues mentioned. In the early 1970s Dolby came on the scene with their noise reduction systems. These were used in studio audio, consumer B formats, and Dolby film improvements. Dolby also wanted to improve FM stereo and came out with their model 334 Dolby B FM encoder to clean up FM stereo noise issues.
I was involved in getting the first NPR FM station converted over to Dolby B FM. When everything was done right it worked very well. We measured about 94 DB SN in Stereo and 104 DB SN in mono FM. Rather impressive improved performance, which could be made even better if one later switched over to the newer and better Dolby C and Dolby S systems, that would have made the SN about 10 DB better.
Dolby FM failed in the marketplace and the Dolby FM 334 system had to be taken out. Why the failure? On the transmission side, there was more audible noise found in the Modulator, STL Link, Audio Console, and music program sources that compromised Dolby FM performance as the Dolby would show up their noise shortcomings. Many stations would not change their other equipment or level practices, but had to engage in the loudness wars to keep listeners.
The Dolby FM Encoder also changed the transmitter pre-emphasis from 75 microseconds down to 25 microseconds which technically was a good improvement to allow more high level high frequency signals without over modulation violations. But FM receivers also needed a switch to change their de-emphasis back and forth from 75 microseconds for non Dolby stations to 25 microseconds for Dolby Stations. One also had to line up signal levels to Dolby standards and have a Dolby B decoder at the audio line output of the tuner or the receiver. All this was all just too much for the general public. Listeners did not usually hear programs of master tapes of wide range classical music. Their taste was for other music types with little dynamic range. Most did not have wide range hi-fi stereo systems either, but instead listened on car radios and table top radios. Dolby FM sounded worse to them with its lower modulation levels and changed pre-emphasis. It sounded duller to them as a result. There were no radio or tuners that would automatically and simultaneously do three things.
1. Change the De-emphasis between 75 and 25 microseconds.
2. Turn the Dolby B decoder on and off, and
3. align the signal levels for proper tracking of the tuner's Dolby decoder to the Dolby FM station.
When tuning to a non dolby station, the above had to revert to the old standard FM settings. Many listeners also thought loud was good and powerful. Some did have reception problems that chronic high modulation levels and various processing helped solve.
Thus Dolby B FM stations lost listeners with Dolby B FM, so they pulled the plug on it. Accordingly, it is hard to actually improve FM on air broadcasting unless one can address and fix all issues at the same time in a systematic way. The marketplace, bad technical compromises, government, and consumers were just not willing to do what it took to make things better for the long term good of FM Broadcasting in a comprehensive rational orderly way. A familiar story.
Anyone want to go back to Crosby stereo or Dolby B or Dolby S FM today? With new low noise quiet analog and digital radio station program sources it would sound fantastic, but no one will fight all the battles to do the job right as it must be done. Adding Surround Sound would cause other headaches and problems.
So over the air FM is, by its market place, standards, technicalities, and FCC rules, limited and stuck where it is as to its sonic performance. Satellite, cable, fiber, internet, etc get around FM broadcast's old obsolete standards and limitations, so they largely take the market.
Hope this helps you. Charlie Richardson"
musichal
poet emeritus
AKAIer, thanks for the post - very interesting. I always noticed, back then, that many receivers included a switch on the rear panel and/or a jack for adding an outboard Dolby decoder. However, I never saw one of these fabled decoders, nor did I ever once hear of a Dolby encoded signal being broadcast anywhere within my receiver's reach - actually I never heard of any anywhere - and was always a bit mystified about the subject. Mainly, I wondered where it was being used. Thanks to your post, I am now fully demystified about one of life's more arcane mysteries...now, if only I could understand politics, religion and her. 
Really, thanks for the post.
Really, thanks for the post.
uxwbill
Lurking in the Shadows
Was Dolby S actually considered for use with FM broadcasts?
vwestlife
Super Member
No, but an alternative FM noise reduction scheme, known as "FMX", was tried in the late '80s. FMX applied the CBS Labs CX noise reduction system (as used on some LPs and LaserDiscs) to the L-R stereo difference component.
Some FMX-equipped receivers were sold, but there were questions about how well the system actually worked, so most stations and radio manufacturers didn't consider it to be a worthwhile investment, and FMX died off after a few years, just like Dolby FM.
KentTeffeteller
Gimpus Stereophilus!
In Europe, the de-emphasis is different. 25 us. Not a loudness curve. Dolby FM is no longer used and didn't catch on. Dolby S was never considered for FM. And too little, too late for mass adoption for cassettes.
vwestlife
Super Member
Europe, and most of the world outside of the Western Hemisphere except for a few Pacific Rim countries, uses 50 uS de-emphasis on their FM tuners. Therefore if you bring a European or Japanese-market tuner over to North America, where we use 75 uS pre-emphasis, it will sound too bright (and the channel spacing on AM will be wrong). The 50 uS curve tops out at around 13 dB at 15 kHz, whereas the 75 uS curve is at 16 dB at 15 kHz, so that's a 3 dB difference at the top end of analog FM's audio response.
On the other hand, if you bring an American FM tuner over to Europe, it will sound too dull, and will be smoking, until its transformer either burns out or catches on fire due to the difference between 120V and 230V AC power!
It is actually the opposite. Using a EUR/JPN transmitter in USA would yield duller sounding whereas using a USA transmitter in EUR/JPN would be duller. The numbers does not reflect to the sound and they can be the inverse of another format. According to Wilhelm, it has little or nothing to do with time, they are the RCs.
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