Dolby FM - why?!

[stevehertz]

Dolby FM was introduced in the late 70s as a noise reduction system for use with FM radio. Despite quite few high end receivers and tuners including the facility, the system failed to take off and died a death shortly afterwards.

So, something I have often pondered is, why was Dolby FM introduced at all? FM broadcasts are by their very nature and design pretty noise free. Right up until the present day, hard core audio/hifi fans cite FM as an excellent source of listening material. By and large, FM broadcasts don't need a noise reduction system, especially when there is built in pre-emphasis anyway. So why have a Dolby FM noise reduction system? The fact that it failed commercially seems to answer the question (it wasn't needed), but nonetheless there must have been some thinking behind it for it to be introduced in the first place - a reason.

To kind of answer my own question, my own view is that apart from Mr Dolby hoping to expand his then burgeoning sales of noise reduction systems into areas other than cassette decks and studios ( I can't blame him!), the system could have some merit for those trying to listen to fringe FM stereo broadcasts where otherwise it may be better to switch to mono reception. In other words an opportunity to listen to a stereo broadcast that without Dolby FM, you would have to listen to in mono. That's about the only situation where I think it would have provided anywhere near a useful contribution. Riding on the back of that, there weren't so many FM stations around in those days so it would probably have been more likely that people were (unknowingly) DXing in order to listen to a stereo station that they liked.

[paulsherwin]

I don't think it was ever used in the UK even on an experimental basis. Quite a few US stations used it for a few years to aid fringe reception, but the main problem with it was that almost no hifi FM tuners were fitted with decoders so sound quality was adversely affected.

Once FM stations started using Optimods in a big way then the few advantages disappeared.

[bluepilot]

I used to know some of the engineers at Capital Radio and they experimented with it in the late 1970s. The problem was that after Dolby processing the sound was quite tinny so they had to cut the treble to make it sound acceptable. I guess the net result is that instead of boosting the quiet sounds you end up cutting the loud ones which rather defeats the object of it. Dolby FM used modified pre-emphasis to overcome that problem so maybe the Capital people were just playing with Dolby B. I can't remember all the details now.

[Hartley118]

Steve, I think that you have an optimistic view of the typical performance of FM stereo when you state:

'FM broadcasts are by their very nature and design pretty noise free. Right up until the present day, hard core audio/hifi fans cite FM as an excellent source of listening material. By and large, FM broadcasts don't need a noise reduction system, especially when there is built in pre-emphasis anyway. So why have a Dolby FM noise reduction system?'

It really depends on your criterion for assessing audibility of background noise. These days, I guess that CDs are the criterion with their quiet background. Only DAB radio can compete with CD. Mono FM is pretty good, but the stereo multiplex process is very inefficient, with its requirement for mono compatibility plus provision for 'Muzak' storecasting on a subcarrier. Unless you have a first class antenna signal (typically millivolts), then switching a tuner from mono to stereo will result in a very audible 20dB increase in background noise. So Dolby noise reduction could have been a useful improvement in its day.

Today, though, with such a crowded FM band, random background noise tends to be mixed in with co-channel birdies which Dolby would struggle to reduce.

Martin

[stevehertz]

Originally Posted by Hartley118

Steve, I think that you have an optimistic view of the typical performance of FM stereo when you state:

'FM broadcasts are by their very nature and design pretty noise free. Right up until the present day, hard core audio/hifi fans cite FM as an excellent source of listening material. By and large, FM broadcasts don't need a noise reduction system, especially when there is built in pre-emphasis anyway. So why have a Dolby FM noise reduction system?'

Well, let me put it another way then, on a strong station it's perfectly quiet enough for me. And that's my criterion, 'good enough'. Once a certain (good) noise level is achieved that does not detract from my listening pleasure, then anything better than that is - to some extent - academic. The noise floors of CD players is ridiculously low. Not saying anything against it, but an FM broadcast is an FM broadcast; a different source of material for a different 'style' of listening, and to me, the noise floor is fine. There's no optimism or 'hope' in that statement, it's a fact, it's how I feel.

[stevehertz]

Originally Posted by bluepilot

I used to know some of the engineers at Capital Radio and they experimented with it in the late 1970s. The problem was that after Dolby processing the sound was quite tinny so they had to cut the treble to make it sound acceptable. I guess the net result is that instead of boosting the quiet sounds you end up cutting the loud ones which rather defeats the object of it. Dolby FM used modified pre-emphasis to overcome that problem so maybe the Capital people were just playing with Dolby B. I can't remember all the details now.

After Dolby processing the processed sound will be tinny if not 'de-processed' at the receiver end? Surely the system worked in such a way that owners of sets with, and owners of sets without Dolby could choose accordingly ? (or it would work automatically). So I'm not getting how the use of Dolby caused tinny sounds when processed and decoded correctly. I dunno, maybe Dolby FM encoded broadcasts were only for use with compatible receivers? It sounds like that was the case! No wonder it failed then!

[paulsherwin]

Proper Dolby FM used modified pre-emphasis and the overall effect was supposed to be neutral on receivers without a decoder, but the encoder still produced effects which serious listeners didn't like.

When received using a decoder it didn't have any obvious effects, but there weren't many of those around, and simple Dolby B does subtly mess up the sound even when decoded correctly, as with cassette tapes. The very people who would be expected to splash out on a Dolby tuner would have been most likely to object to the process on sound quality grounds.

[Grubhead]

I must say I have never heard of Dolby FM before. It sounds like a Radio Station name to me!
I remember Radio Four doing binaural stereo transmissions. I think I still have a tape recording of the Mastermind presenter out in the countryside with great sound effects. If you did not have a set with it built in you could use headphones and it really spaced out the sound.
Would Dolby FM get rid of the birdy type whistles you would get with FM?
I would have thought that it would have benefited classical stations. But Dolby on pop not needed I would have thought.

[Nuvistor]

I could not see it getting rid of birdies, these I understand are interactions between stations on our crowded FM band, not something we had when FM first started.
Classical, Jazz, Pop, its all music and those who like each type would probably want the best.
I have not heard of Dolby FM and looking at the basic explanation of how it works looks like a waste of time, bet the sales person didn't say that though.

Frank

[paulsherwin]

It just improved the signal to noise ratio, particularly background hiss, but the general opinion was that it was more trouble than it was worth. Dolby did lobby hard for it in the US for a while.

[stevehertz]

Originally Posted by paulsherwin

It just improved the signal to noise ratio, particularly background hiss, but the general opinion was that it was more trouble than it was worth.

I think that just about sums it up then Paul.

[Hartley118]

The background hiss level on stereo FM with a middling kind of signal strength is not unlike that on a compact cassette, so it's interesting to ponder the failure of Dolby's entirely logical and sensible drive to improve it.

I guess it may be something to do with the fact that Dolby's success started with tape and not radio. Around 1970, professional studios had a clear need to reduce the noise level of analogue tape, particularly in the way that hiss could build up over multiple generations of recording. Dolby A turned out to be the ideal solution to the customer's problem and was a huge commercial success - the perfect business school case study.

It's perhaps more of a puzzle that Dolby B was such a success with compact cassettes. Many of the arguments used in this thread about FM stereo radio's adequacy would have applied equally to Compact Cassettes - to the average listener in their early days they were 'Good Enough', so why bother with Dolby?

I suspect that it was Ray Dolby's personal charm and persistence with the influential record companies that persuaded them that Dolby B could enable the cassette to approach the quality available from vinyl record - but without the pops and clicks.

Subsequently of course, high quality cassette players from the likes of Nakamichi did exploit the available quality, but maybe it was really the Walkman that exploited Dolby B for the masses. Signal to noise ratio does tend to be more critical for headphone listening, and maybe the Walkman wouldn't have succeeded at all without Dolby B.

Martin

[paulsherwin]

As it happens, the arrival of Dolby B on cassette decks coincided with the arrival of dramatically quieter tape formulations, particularly from Japan. It's arguable that Dolby B would never have taken off if these formulations had been available a couple of years earlier.

The hiss level on early 70s cassette recordings was really bad, and much worse than typical FM stereo hiss.

[Grubhead]

I suspect that it was just a question of adding the Dolby circuit to the cassette recorders. When the Dolby IC's were made it would have cut the cost no end. It was then marketed as a hi-fi improvement for the sound. Dolby logo's were as often as big as the brand name! Which tells you something.
Recorded cassettes also carried a note with the Dolby recorded cassette, saying on none Dolby equipment it would sound brighter and clearer. Since many people used cassettes for recording sticking on the Dolby meant the recordings were all done with Dolby encoded. Whereas it required the Radio engineers to install and maintain the Dolby on FM radio. The cost of installing it would eat into the station's budget, so I can't see why they would install it.
If you were recording an FM Radio transmission with the Dolby on, then surely that would have killed some of the station hiss?

[vidjoman]

Originally Posted by Grubhead

If you were recording an FM Radio transmission with the Dolby on, then surely that would have killed some of the station hiss?

If the Dolby circuit was correctly set up on a cassette recorder than it will not cut FM station hiss - it should playback exactly what was recorded, hiss and all.

[paulsherwin]

Dolby reduces noise from the tape and won't affect the material being recorded. Some manufacturers did offer noise gates before Dolby became universal - Philips had a design called DNR (Dynamic Noise Reduction) which only operated on playback and chopped off all the HF when the signal fell to a certain level. Unfortunately noise gates are very intrusive so result in a poor listening experience - most people preferred to turn them off and let their brains adjust to the hiss.

[stevehertz]

Originally Posted by paulsherwin

As it happens, the arrival of Dolby B on cassette decks coincided with the arrival of dramatically quieter tape formulations, particularly from Japan. It's arguable that Dolby B would never have taken off if these formulations had been available a couple of years earlier.

The hiss level on early 70s cassette recordings was really bad, and much worse than typical FM stereo hiss.

I think we're talking about the migration of the cassette deck/player from being a fun, convenient way of 'tape recording' (often pop material from the radio) to becoming a valued hifi component. In the former, the amount of hiss didn't really bother the average person, they were so grateful to get that week's top 20 for free. But the dedicated hifi man was a different animal, he wanted hifi performance, and the Japanese cassette deck and tape manufacturers fought hard to raise the performance of the genre, and they succeeded admirably, certainly at the high end.

Ironically, the quality of video tape formulations also became very good at about the time that video recorders were being overtaken by DVD.

It just improved the signal to noise ratio

So would a good aerial, cheaper and it works with non Dolby stations too.

[Andrew2]

Originally Posted by paulsherwin

Dolby reduces noise from the tape and won't affect the material being recorded. Some manufacturers did offer noise gates before Dolby became universal - Philips had a design called DNR (Dynamic Noise Reduction) which only operated on playback and chopped off all the HF when the signal fell to a certain level. Unfortunately noise gates are very intrusive so result in a poor listening experience - most people preferred to turn them off and let their brains adjust to the hiss.

I remember (sometime in the early 80's I think) repairing a Philips music centre which had DNR on the cassette deck. I was most impressed! I was expecting it to be a very noticeable, heavy-handed thing, but in use it was quite subtle. Even with my 'engineer's ears' and my knowledge of what it was doing I could only just detect the system in action. Yer average punter would not have been aware of the jiggery-pokery at all.
At the other end of the scale, my first experience of DBX was not happy. It seemed to make the sound 'thick', and this time my engineer's ears were not pleased. Same with Dolby C, which had the same effect.

[stevehertz]

Originally Posted by merlinmaxwell

So would a good aerial, cheaper and it works with non Dolby stations too.

Good point - and another reason why it failed commercially!