Harry Maynard in his program “Men of Hi-Fi” on WNYC interviews Adrian Horne of Dolby Laboratories, London.
------- Ray Dolby with an early unit.
Maynard: Good evening ladies and gentlemen.
We are going to revisit the Dolby noise reduction system. My guest this evening is Adrian Horne, who is the Licensing Manager for the Dolby Laboratories Incorporated. They are headquartered in London, England. I might add we are also going to play you two demonstration tapes for cassettes, one that is included with the 4760, the 3M machine that incorporates the Dolby circuit, and we are also going to play you an Advent Dolbyized cassette, and we are going to send them out still Dolbyized so you will have a chance to see how they sound with the Dolby characteristic. It seems to me, just a sort of superficial overview, that most manufacturers are using the B-system in cassette recorders. Is that right?
Horne: Certainly that is correct. The cassette has shown itself to be a very interesting product. It had very serious problems when first introduced but, as the major parameters of performance of the cassette machine have improved, it has shown itself to be capable of producing as good quality as almost any other recording medium used in consumer audio.
Maynard: Yes, as a matter of fact when I turn on the Wollensak 4760 and put on a Dolbyized cassette right now, I continually get up to see if it is running.
It is so quiet even when compared with a virgin disc or a good reel to reel tape. Why is that so? I think I know the answer, but .. .
Horne: The answer is that with a virgin disc, even new out of the sleeve, there are going to be some ticks and pops occurring from particles of dust that have been attracted by static electricity.
Any tape recorder is bound to produce some sort of noise from the tape unless you have the benefit of noise reduction to minimize this noise but then, even on the lead-in tape with which the cassette is beginning, the noise reduction circuit is working and lowering the level of the signal that comes out, so that you lose the basic hiss that would otherwise be present.
Maynard: I know a lot of our listeners probably know how Dolby equipment works, but I find that even when I am writing articles on it, I have to re-train myself to put this in the simplest understandable terms. What is your favorite current explanation, simple explanation, of how the Dolby system works?
Horne: For the simplest explanation the thing is first of all, I think, to understand clearly what the Dolby circuit is trying to do, and what it is doing is trying to reduce the effect of noise added by the recording process. Any recording process, or for that matter, transmission process, adds noise, but with a slow speed tape with narrow tracks, which is the case on cassettes in particular, the hiss generated by the tape becomes particularly obtrusive when the music is quiet. Now it is quite easy to design an electronic circuit which can take out that sort of quiet hiss, but such a circuit would not be able to differentiate between music and the hiss itself.
Maynard: So it lops off the highs.
Horne: It takes off anything that's there, when it's functioning. Now, to deal with this, we arrange that the music, as it is recorded, has the quiet sections recorded just a little bit louder than they would have been otherwise.
Maynard: That is what you mean when you use the word stretching. Is that it?
Horne: Yes, stretching is the word the professionals use, but we are now using, perhaps an easier word to understand because it has become commonly used with home equipment, the term "encoding", and when a Dolby tape is encoded the quiet high frequency sections, which are most disturbed by the presence of hiss, are made a little bit louder as they go on the tape.
When you play back through the Dolby circuit these sections are brought down as the hiss is brought down, and they are brought down to exactly the level they were before they entered the encoding Dolby circuit at the beginning of the whole process. So you get back the original program material, but you have this hiss missing.
Maynard: You sort of kick it out the back door. Is that right? How would you describe that kicking it out the back door principle?
Horne: That's technically described as a process of expansion, of making the quiet signals quieter in relationship to the loud signals, and that's why the hiss disappears.
Maynard: Now, other people before Dolby had expansion systems, didn't they?
Horne: Yes indeed.
Maynard: I can remember one person, who will go nameless, but he is quite famous in this business. When I invited Ray Dolby on my program, he said "Don't have that man on your program. That whole Dolby process is a fraud. This man is a phoney. It will never work". I found out, right after that, that he asked for the U.S. agency for Dolby equipment.
Horne: Now the Dolby system does have the advantage that it works, and it works because of a very important basic concept which Ray Dolby developed in the middle 1960's. The concept of compression and expansion has .. .
Maynard: It's been around for years.
Horne: It's been around since the 1930's.
Maynard: Well, I remember I had a FM tuner receiver called the "H.H. Scott" and it had, what I guess was a less sophisticated version of what, now, Philips call the DNL system, didn't it.
Sort of electronic gate, wasn't it?
Horne: That's right. This was another expansion system, as is the DNL system. The problem with both of these was that neither of them relied on encoding the signal first. The result, therefore, was that when the circuits operated you were bound to lose some of the signal with the noise, and this, we believe, is not as satisfactory an approach as to guarantee the listener that he gets the original program material back without any degradation.
Maynard: As hi-fi equipment gets better and better, and it seems to be getting better and better with Solid State; it's quieter, its signal to noise ratio is constantly being improved, all forms of distortion in better hi-fi equipment are minimized; it seems to me that this just gives you people a bigger and bigger market, or more reasons for using a Dolby circuit.
Is that a fair statement?
Horne: That's a very fair statement. It's an interesting thing that as you take the opportunity by use of the Dolby system to reduce noise, many other deficiencies become apparent which it is possible to remove with good engineering and there is the opportunity then to produce even better equipment. This is a constant process.
Maynard: Well there is another thing that I noticed in the very first records that were Dolbyized in the United States. The name of this record manufacturer will go nameless, but it showed up his record surfaces in a sense. I mean, it's like putting a microscope on a woman's face. Then what was coming through was no longer the high level hiss that is in the master tape, but record surface was beginning to come through. I remember when I interviewed Ray Dolby I brought up this point, and I said "Will this force the record manufacturers to make quieter records". What's your comment on that I bring the subject up again.
Horne: Well, we believe that that has happened, that recording techniques have improved because of the .. .
Maynard: In the record making .. .
Horne: Record making techniques, disc making techniques, and basic recording techniques also have improved because the blanket of quiet hiss that was present, even with professional recordings, concealed a lot of little errors in technique which, if you like, were unmasked by the use of noise reduction. The result is that recording techniques are vastly improved now. Looking now at the cassette, which is the primary medium with which the B-system is concerned, the companies which have been longest established in producing B-Type cassettes are producing much better cassettes than were available three years ago.
Maynard: Oh yes, and as a matter of fact we are going to demonstrate that in a very few moments, just how good cassettes now sound. And they're getting better and better. I heard that BASF chromium dioxide cassettes with special mechanics, and granted it is an extraordinarily expensive cassette, it still has a fantastic dynamic range.
Horne: It's exceptional and we believe, from our own experiments, that when cassettes of this type are used for duplicating-mass duplicating pre-recorded material-they will probably be, in all respects, better than the equivalent disc.
Maynard: Well now, there are basically two Dolby systems, aren't there? There is the A-system which the professionals, the record companies use for the master tape, isn't that right?
Horne: That is correct, yes.
Maynard: And then there is the B system which is what the consumer uses when he switches the Dolby circuit on let's say, the 4760, which is the one we are going to play all the demonstration material on this evening. He'll see a Dolby switch, won't he.
Horne: Right, and that actuates a B circuit.
Maynard: Now will you explain. Go ahead.
Horne: The A-system was the original system developed with the objective of dealing with the most important noise problem, if you like, and that was the noise generated in professional recording. This is a complex system. It divides the program material into four frequency bands and deals with each individually. As you can imagine, professional equipment built to the highest standards which does something as complex as this is expensive, $740 for a single channel, and a lot more when it was first introduced. Obviously such equipment was not a proposition for the consumer.
Maynard: I have heard it said that the development of solid state electronics made the Dolby system possible. Is that a fair statement? Could it have been done with tubes?
Horne: It could have been done with tubes. Interestingly, some of our first work was done using tubes, but what we now get on to a board which is 9" x 6" took up almost a rackful of equipment; imagine the difference. So, from a practical point of view, I think that the system could not really have been accepted widely if solid state technology were not available.
Maynard: I have also heard it said that the initial resistance to the Dolby was largely due to a misunderstanding of the way it worked. I can remember reading some of the critical questions that were asked. I understand that you have to have a de-stretcher that gives you a mirror image.
Horne: Right, it's a mirror image process. This is the essential characteristic of the Dolby system, if you like, and it is an encumbrance as well, because it means that if you have recorded a Dolby tape and then want to cut a disc from it, you have to have a Dolby noise reduction unit in the decode mode right next to the cutting lathe and it means that if you make a tape in one country and want to send it to another for cutting, you have to be sure that the company who is going to do the cutting overseas has Dolby equipment, so in the early days this was quite a restriction in getting the system established.
Maynard: Yes, I can remember one critic brought up the question that suppose somebody comes across these recordings in three or four hundred years when they are excavating our civilization and they are stretched and they don't have a de-stretcher, isn't this going to be a horrible predicament? I can remember a lot of resistance you ran into among major recording companies. You have enumerated some of this. Weren't there some other resistance to…
Horne: There were indeed. There is an interesting psycho-acoustic effect that we had to deal with here which works like this. If you take out hiss the listener, when comparing the same program material at the same level which has hiss with a Dolby decoded version of the signal which has had the hiss removed, suspects that the high frequency quality of the Dolby treated program has been degraded, that the highs are missing. This isn't in fact the case and it is quite easy to demonstrate this by adding tape hiss back into the decoded Dolby signal. Then, comparing the two again, (the decoded Dolby signal with the non-Dolby), the high frequencies appear to have come back again. This proves that it is your ear that is confused and not the actual circuit itself.
Maynard: The Dolby system takes advantage of certain, you might say, basic psycho-acoustic phenomena. Would you explain that to our listeners?
Horne: Sure, the most important of these is the concept of masking. If you have a loud signal, as a generalization you can say you will have difficulty in hearing a quiet signal at the same time.
However, that's too big a generalization, and the way it works when we describe it more precisely is that if you have got a loud low frequency signal you won't hear quiet low frequency signals, but you may still be able to hear quiet high frequency, signals.
You know this; that if you are talking to somebody near a jet taking off, there is a lot of low frequency noise as the engines work up, but if you whisper in a high pitched voice it I is quite easy for the other person to understand you. Now, in the recording business, you may well have music where there are low frequency sounds-somebody beating a bass drum-and yet no loud high frequencies. In that case, the masking effect is not going to protect you from the high frequency noise that is basically part of the recording process.
This is the reason why the Dolby system breaks into four bands in the professional system. The masking will look after noises in its own area in the presence of a loud signal which would switch off the noise reduction circuit, but in a distant area across the audio spectrum the noise reduction circuit must still work, and so must be in a separate frequency band.
Maynard: Dolby is an American, isn't he?
Horne: Ray Dolby is indeed an American.
Maynard: And he worked for Ampex?
Horne: That's right. He lived for quite a long time in the Bay area, and in fact the thing that first took him to England was winning a fellowship to Cambridge University where he took his Ph.D. and did some post-doctoral research back in the late 50's and early 60's.
Maynard: I'm still curious about early resistances to the Dolby system. From where I judged it, and this was as an outsider looking in, and somebody who is vitally interested in anything that will improve hi-fi, there were an awful lot of misunderstandings about Dolby noise reduction that we haven't discussed. I suppose it's that old phenomena--we're down on what we're up on. What were some of the early resistances that Ray ran into when he was trying to convince people, other than the ones that we have already discussed, on the use of the Dolby. I know several recording engineers at several major recording companies were sort of agin it, and now my spies tell me that they insist on the use of the Dolby, the very people who fought it originally.
Horne: The problem is that it seems to be magic, at the first glance flying in the face of the laws every recording engineer has known, that noise is one of the great hazards of recording which you have got to do everything you can to avoid, but that it is inevitable. Suddenly Ray Dolby appears with a big grey box under his arm and says this will take it away. It had happened before. There were five noise reduction systems on the market in 1967.
Maynard: Were they being widely used?
Horne: No. In some cases they were being used by the companies who had invented them and in another were being promoted alongside other audio equipment which had a good reputation and was widely used, made by the same company. But they all had some problem. Either they didn't really work, and that was perhaps the commonest thing, or else they were extravagant in tape, which is no solution really, or else they called for radical changes in recording techniques used in the studio. All of these, of course, are something the studio is going to resist, because it has worked very hard to establish really clear cut and firm recording techniques and practices in order to maintain the standards at the highest possible level. One of the advantages of the A-system, therefore, was that it didn't call for any changes, but it did uncover all sorts of things that just weren't noticeable, that engineers just weren't aware of, before they had the benefit of the noise reduction.
Maynard: Such as, for example.
Horne: There are certain noise modulation effects, that is to say, variations in the apparent level of noise on a tape which were inevitably there, when recording without the Dolby noise reduction system, which it helped remove and which therefore led some engineers to believe that the Dolby recording process was modifying the signal adversely.
What you find then, with careful comparison of a Dolby encoded and decoded signal with the original source materials is that, in fact, there has been no degrading, that it's the conventional, or what was the conventional recording technique, without noise reduction, which has been introducing the changes.
One of the most thorough checks, one that is most easy to get hold of, if you like, is one that was used by Columbia before they committed themselves in a very large way to use of Dolby noise reduction, here in New York. They hitched together 8 of the original A301 noise reduction units, first of all, one channel in encode and the second channel in decode, and then they encoded and decoded again, and they did this eight times. They then compared the signal that had been in and out and in and out through all these noise reduction systems with a signal that had just come down a wire alongside and they couldn't hear any difference.
Maynard: I think that when we played that last demonstration tape, you had some very interesting comments to make on it. Now we sent it out stretched. That's not the way the con sumer would hear it in his home if he had a Dolby system, it is?
Horne: Right.
Maynard: I want to make that very clear.
Horne: Sure. It would sound a little less bright in the quieter passages. You would not notice any difference in the loud passages because, remember, one of the main things about the Dolby circuit is that all the time there is one path that is open, that is just passing the signal through without any modification at all.
Maynard: Well, the Dolby system, the B-system for the cassette, was almost a necessity to put that old statement--necessity is the mother of invention. Because of the high signal to noise ratio of a cassette or .. .
Horne:... poor ratio.
Maynard: That's much better, poor signal to noise ratio or higher inherent noise. The tape companies have been working very hard to improve the quality of cassette tape. Most people don't understand that some of the world's best tape is going into a cassette. The problem is not so severe in the reel-to-reel situations, but now I notice that Revox has got a reel-to-reel recorder with Dolby facilities. What other manufacturers are putting Dolby in their reel-to-reel machines on a semi-professional product, a product that a consumer would be apt to buy? I know Tandberg has told me that they are going to be coming out with a Dolbyized reel-to-reel player. What are some of the other manufacturers?
Horne: Another one is Ferrograph.
Maynard: That's a British company?
Horne: Right. These are the three which are actually under way at present.
We are expecting that some of the Japanese manufacturers will as well, but they have universally elected to produce a cassette deck first.
Maynard: I can remember one reel-to-reel manufacturer who said that this tape player was so good-and he will go nameless-was so good that they didn't need the Dolby. What is your reaction to the statement?
Horne: I think we feel that it's a rich man that can throw away 10dB of improvement in signal-to-noise ratio.
Maynard: Yes. What about the dynamic range? What effect does Dolby have on the dynamic range of a recording?
Horne: Effectively, it allows you to increase it because it takes the noise further away from the maximum level that you can get on and so .. .
Maynard: You have more what? What do they call it? Horn: You have more headroom.
Maynard: More headroom. We will explain that to our listeners.
Horne: It's a very important concept when dealing with cassettes. It is not quite so important if your own recording is done on an open reel recorder running fairly fast, because in that case, if you overstep the mark a little bit, if you record a little too hot, the tape will distort a little bit; more than you would like, but it won't have a really disastrous effect.
Maynard: It won't saturate so quickly, because there is so much more headroom there, is this what you are saying?
Horne: That's right, there is more room available, but you know the cassette tape is very narrow, the oxide on the cassette itself is very thin and this means that if you record too loud, if you put on too much signal, you get really awful distortion, but always you've got down lurking below you this hiss level which you are trying to get away from. With noise reduction you can take the hiss level away down, 10dB down, equivalent to running the tape ten times as fast and this means that you don't have to be pushing against the ceiling, against the maximum level that will go on the tape, all the time. You can spare a little bit of extra room and the recordings aren't under such risk of overload then.
Maynard: WQXR in New York has been using the Dolby B-system, not the Dolby A-system. As a matter of fact we did an experimental broadcast using the Dolby A, but we didn't send it out stretched, we just used it to Dolbyize the actual recording of the broadcast we made, but we didn't send it out. But QXR has been sending out a Dolbyized signal, isn't that right?
Horne: That's right, and the most interesting thing of this perhaps is that they have, in doing this, demonstrated that a Dolby B-Type broadcast is fully compatible. There is no problem in listening to this if you don't have Dolby equipment at home.
Maynard: You mean it sound slightly brighter?
Horne: It will sound a little brighter, but it will sound fine. You just won't get any reduction in the level of background FM hiss which, incidentally, is very similar in quality to the hiss you get from a low speed tape, but you know that when WQXR were deciding to go ahead with Dolby broadcasting....
Maynard: Are they Dolbyizing all of their broadcasts?
Horne: Yes. They are Dolbyizing 100%, and they began to do this five weeks before the announcement, and do you know that they had absolutely no complaints whatsoever in that period of five weeks. Only two of their very many listeners even detected that it was a Dolby broadcast, and this only because once a week they had a one hour program which was announced as Dolbyized. It was a discussion of hi-fi and in the course of the discussion Dolby broadcasts were put out and a couple of guys, listening to this, noticed that the signal didn't change at the end of the program. That told them that it was still Dolby, but nobody else noticed.
Maynard: Then let's face it, most hi-fi systems probably need a slight high and boost anyway, wouldn't you say?
Horne: I think that's fair comment.
Maynard: I mean I have a feeling, I can't prove this and it's based on no engineering knowledge at all of these facts, but I think there is probably so much roll-off in the average, both in going out and coming back through the average system that you probably get a slightly improved signal from the listener's standpoint.
Horne: I think it's quite likely. It is certainly true on lower cost equipment, because one of the difficult things in life is to produce a good clean high frequency signal from a low cost speaker. So you can be sure that the majority of listeners, who don't have $500 or $1000 to spend on hi-fi equipment, are actually going to find that the Dolbyized signal is fine.
Maynard: What's your reaction to chromium dioxide?
Horne: We think that this is an excellent development. It does permit an even better performance than can be obtained on most of the iron oxide tape that is available to date. I don't think it is a fair thing at this time to debate whether some of the latest high energy iron oxide tapes are achieving the same benefits but, as compared with the typical iron oxide tapes, the typical high quality tape, even, chromium dioxide as recorded by Advent, will give you maybe 3 or 4 dB better signal-to-noise ratio, and better high frequency response, so that some of the most exciting music sounds just that little bit more exciting than it did before.
Maynard: You told me about the uses of Dolby noise reduction in motion picture making. Do you want to tell us something about that?
Horne: Sure. This is one of the things we have been getting very excited about over the last year. The system has been used in the movie industry in the way it is used, for instance, in making discs in recording studios, for quite some time, that is to say, in the sound divisions of the film studios they have been making A-type Dolby recordings and processing the audio for the films in A type form until they got to the point of putting the signal on to the soundtrack. Now we have the opportunity to put an A-type encoded soundtrack right there on the final print of the film and to decode it in the cinema, and this will give the opportunity to get vastly improved sound in the cinema with a significant reduction in noise.
Maynard: I imagine that down the road a piece, as we like to say in America, there are many other potential uses of the Dolby, uses in video systems, perhaps? What are some of the other potential uses?
Horne: Well, any situation where you are transmitting an electronic signal you are going to meet trouble with noise.
Maynard: But most people don't think of noise in connection with video. Explain that one.
Horne: Well, the problem there is lack of definition in greys, and if you think of an action replay and compare it with a news broadcast you understand what noise does to a video picture.
Maynard: So we have that to look forward to.
Horne: That's one thing that we are looking forward to and it will be coming along one of these days.
Maynard: Well good. I want to thank my guest, Adrian Horne. I hope you will come back. Maybe the next time we have him on he'll tell us what is happening to the hi-fi scene in England and also what the state of Dolbyized broadcasts are in England. Are you Dolbyizing any broadcasts in England?
Horne: A little experimental broadcasting has been done.
Maynard: Well, I want to thank my guest this evening. Revisiting the Dolby noise reduction system my guest has been Adrian Home, Licensing Manager of Dolby Laboratories Incorporated.
Thank you Adrian for being on this program.
Horne: Thank you Harry. I have enjoyed my evening with you.
(Audio magazine, Feb. 1973)
Also see:
Construct a Dynamic Noise Filter (June 1975)
A New Standard in Turntable Speed Constancy (June 1978)
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