Talk:Dolby noise-reduction system

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You can always listen to a dolby tape on a not-dolby compatible (i.e. linear) tape deck - how is that possible? The material should sound awkward, but it doesn't. Is there something like backwards compatibility implemented in Dolby NR technology? Thanks, --Abdull 20:12, 10 Jun 2005 (UTC)

Dolby B simply compands the dynamic range of the audio to reduce noise. See Companding, if it's still unclear.

I also disagree with the use of Companding as a catch-all term for Dolby NR. Dolby is more of a pre-emphasis system while dbx is heavily companding based.

Actually, Dolby B isn't quite as simple as that. For one thing, it is frequency-dependent, operating principally above 5 kHz. It also doesn't really compress the dynamic range per se. By improving the signal-to-noise ratio during recording, the net effect is to more closely preserve the dynamic range of the original recording. Without decoding during playback, the signal will contain boosted high-frequency information (including tape hiss). It is still listenable—and may even sound better than decoded playback unless the Dolby tracking is accurate, which it often isn't—but it will contain surplus high frequencies and noise.Rivertorch 02:42, 7 October 2006 (UTC)[reply]

To the trained ear* a Dolby B recording played on non-Dolby B equipment would sound distorted, though people with trained ears would be using equipment with noise reduction, or more likely hand-tweaked record decks connected to industrial speakers via solid gold cables. *(probably if a normal person compared the playback with and without NR, they'd notice the difference as well as the extra noise) boffy_b 01:35, 6 January 2006 (UTC)[reply]

In my experience, a Dolby B recording, played back on non-Dolby B equipment, sounds a little bright - enough for the average listener to recognize if pointed out - and can be reasonably well corrected by reducing the treble tone control. However, a Dolby C recording, played back on non-Dolby equipment sounds painfully bright, with wildly variable levels of tape hiss breaking through. Tone controls cannot tame this result.David Clewlow (talk) 23:20, 4 January 2015 (UTC)[reply]

Can someone write a description of Dolby S noise reduction as used on domestic cassettes.

Dolby S was not used on US domesitc cassettes in the pre-recorded market. Lots of reasons behind it. Mostly because Dolby B was out first and was able to gain market acceptance, it was also the cheapest and easiest to implement. Dolby B tapes also didn't sound as bad when played on non Dolby playback systems, unlike C or S which tend to sound off without thier respective systems. Some places issued tapes in Dolby C and i imagine possibly Dolby S, but most of these were special orders from places specializing in audiophile releases, but they were never mass distributed. Most recordings using C or S are indviual recordings.DewDude 16:58 06 Oct 2006

Is Dolby SR noise-reduction (for professional audio recording) the same as the SR-encoding used on 35mm motion picture (film) prints? Can this be mentioned in the main article?

Before Dolby Digital, DTS, Sony SDDS, most "Dolby-Stereo" (cinema surround sound) soundtracks were distributed on the 35mm optical print, encoded in Dolby A (I think.) Sometime in the 1990s, Dolby upgraded their optical sound processors (for movie theaters) to support Dolby SR. —Preceding unsigned comment added by 67.127.228.164 (talk) 00:15, 19 October 2008 (UTC)[reply]

The description of Dolby HX Pro is inadequate, and describes tape bias more than Dolby HX Pro. Can someone expand please?

No, not really. The reason being that HX Pro was a system that dynmically modified the bias signal applied to the recording dependant of the incoming audio signal. Higher frequencies don't need as much bias to be recorded as they're almost liner to the tape already. It's not a noise reduction method by any means, just an improvement of the way the audio was recorded onto the tape which would have a positive effect when played back on ANY player. It's difficult to expand it any further. --DewDude 16:50 06 Oct 2006

The link "Commercializing the Dolby Noise Reduction System" is broken and I could not find the appropriate article on a search of the target website (or elsewhere). --87.114.10.157 16:17, 4 December 2006 (UTC)[reply]

This page should probably have a discussion of Dolby E, even thought it's not really a noise reduction system. jhawkinson 03:56, 24 September 2007 (UTC)[reply]

The following sentence in the dolby hx section does not make sense:

"With fixed frequency and amplitude high frequency strong signals the amount of bias signal needed is reduced."

What on Earth does that mean? No really, I can't even guess what is trying to be said in this sentence.

I can't edit the text myself because I have absolutely no clue what was supposed to be intended by this sentence. I don't think it's simply a case of missing punctuation - it's absolute gibberish.

I hope someone can rewrite it,

Thanks

Daniel —Preceding unsigned comment added by Dpolwarth (talk • contribs) 23:10, 17 April 2008 (UTC)[reply]

I fixed the sentence, but the entire article needs copyediting. I'll try to get to that later today, but I'm wondering whether the HX section really shouldn't have its own article. The article, which is misnamed in the first place because it's about systems (plural), has "noise reduction" in the title. Although HX and HX Pro can boost the S/N ratio slightly, they are not NR systems per se. Rivertorch (talk) 23:48, 17 April 2008 (UTC)[reply]

What makes even less sense is that HX Pro is not a noise reduction system (it even notes it at the start of its section!), yet it appears in a noise reduction article. Surely it should be split out? danno 19:54, 8 September 2009 (UTC)[reply]

Agreed to an extent. Dolby HX Pro isn't a noise reduction system, but it does help any 'flavour' of Dolby NR to track more accurately on playback, so I've amended the section accordingly. Although it's difficult to find any supporting citations, it's an inevitable consequence of the improved amplitude linearity that HX Pro brings to the tape itself during the recording phase. This effect is particularly noticeable (and very easily measurable) when trying to calibrate Dolby C on a non-HX Pro deck versus an HX Pro deck. All else being equal, an HX Pro deck will always outperform one without it in this respect, particularly when using Type-I or Type-II tapes. Gruntsplat (talk) 13:09, 14 December 2016 (UTC)[reply]

Yes, HX Pro probably deserves its own article. (Fwiw, while HX Pro isn't a noise reduction system per se, it does improve the S/N ratio by permitting higher recording levels.) Rivertorch (talk) 15:58, 2 April 2010 (UTC)[reply]

About 25 years ago when as the engineer for a radio station, I read an article in a technical magazine on the history of the Dolby noise reduction system. It mentioned that the reason why the Doors 1st record has such a bright high end sound is that the Dolby playback settings were accidentally not turned on after the tapes had been encoded. The explanation given was that it was new technology at the time and a secondary recording engineer was not familiar with it. Timeline wise this seems plausible. Has anyone found any verification of this?22yearswothanks (talk) 02:43, 21 March 2010 (UTC)[reply]

It is premature to say that analog recording is obsolete. Even some CDs are going back to analog remastering to try to improve their sound. Our latest auditions of music on Bluyray, mainly concert videos, indicate that there is still a wide gap between the actual music produced by real instruments and the digitally recorded rendition of these. Analog is still the most capable of the trueist reproduction of the music dynamics and spatial dimensionality, discounting the high SNR possible with digital recordings. Digital is mainly preferred for its convenience.(207.35.47.66 (talk) 00:01, 23 March 2011 (UTC)RVK, March 22, 2011)[reply]

The current version reads; In other words, Dolby NR is not becoming obsolete for analog recording, but analog recording itself is less prevalent as digital recording has become more widespread. This seems quite reasonable and factual without being POV or OR, regardless of one's opinion. Ubcule (talk) 12:29, 4 September 2013 (UTC)[reply]

The above cited current version surprised me when I got to the end of it and saw that its neutrality was questioned. I thought it was a very fair statement. Yes, some analog recording is still being done, but the mainstream uses of Dolby have more or less evaporated. Also, the people using analog tape are most often the die-hard purists many of whom did not embrace any noise reduction system to begin with. So, I think it is a fair statement. Rlhess (talk) 21:33, 22 April 2015 (UTC)[reply]

In reply to immediately above: That depends on a person's definition of "die-hard purists". True audiophiles nearly always embraced Dolby B and C as they'd usually have decks of sufficiently high quality for both to work entirely correctly thus improving the perceptual transparency of the medium. The improvement with Dolby C arguably brought cassette very close to CD-quality at sensible listening volumes with 20dB of noise reduction along with greatly extended reproducible frequency range at normal recording levels with the aid of spectral skewing. 20Hz to 20kHz (+/- 0.5dB) at 0dB record/playback level is a reality on some high-end cassette decks with Dolby C even with budget Type-II tapes. Nearly all of those who've ever complained about Dolby B or C colouring the sound in some way either haven't heard it working properly or have used suspect testing methodology. The problem of poorly performing decks crippling noise reduction transparency was the reason for Dolby themselves insisting that any deck to be installed with Dolby S must pass their own tests for meeting certain minimum performance criteria. GIGO. Gruntsplat (talk) 13:11, 13 December 2016 (UTC)[reply]

The neutrality of the claim made on this talk page of 'analog superiority' is also in dispute. Blind controlled studies where the listener has no knowledge of the actual sound source have proven time after time that current digital technology, when inserted into a channel, is audibly transparent compared to a single straight analog channel when playing a live performance in an isolated room at comfortable listening levels (actually the studies proved this with CD-audio digital technology that is 'inferior' to current technology). Claim of 'analog superiority' is only encyclopedic in the analog-vs-digital article on the (dying) controversy and is now widely recognized as fallacious.CherylJosie (talk) 20:56, 4 November 2013 (UTC)[reply]

The Dolby C section refers to audio 'spectral skewing' but links to a Wikipedia article on gas chromatography where spectral skewing refers to the change in detected mass spectrum due to the destruction of some (lighter?) components from the ionization(?) process. I suspect there may be another form of 'spectral skewing' that refers to audio spectrum or some similar term such as 'spectral masking' etc. but the link to mass spectrometry is obviously wrong. Does anyone know what the correct technical explanation is? CherylJosie (talk) 20:01, 4 November 2013 (UTC)[reply]

I removed the offending bit because the entire sentence was opaque and baffling. It was supposed to be informing the reader about the technical basis for Dolby C but it revealed nothing and just caused more questions. Binksternet (talk) 20:54, 4 November 2013 (UTC)[reply]

Spectral skewing was part of Dolby SR for professional use, not for Dolby C. 89.204.155.163 (talk) 03:27, 26 October 2015 (UTC)[reply]

The above statement is false. Spectral skewing is part of Dolby C and always has been. A quick read of any of the freely available datasheets for Dolby B-C NR devices makes this perfectly clear. Please check reputable sources to confirm statements before claiming them to be fact. ^[1] Gruntsplat (talk) 12:00, 13 December 2016 (UTC)[reply]

There is no discussion about the belief that Dolby B "dulled" the sound. About 30 years ago, I ran uncontrolled tests using a Nakamichi NR-200 simultaneous encode/decode Dolby B/C processor, and a similar dbx II processor, without a tape recorder in the path. I convinced myself that the claim was correct. Dolby B slightly "dulled" the sound, while dbx had no apparent effect. I have a theory as to why this occurred (Dolby's clipping of overshoots during recording caused incorrect playback decoding). Of course, now that Dolby and dbx are effectively obsolete for tape recording, what difference does it make? WilliamSommerwerck (talk) 20:57, 21 March 2014 (UTC)[reply]

If you wanted to add something about this issue then you would need to refer to previously published sources rather than your own experience. Unfortunately, much of the 1980s audio engineering literature is still not digitized, so you would have to study the magazines and journals in archives where they can be found. Coincidentally, Dolby Labs in San Francisco has a huge library of such magazines and if you make prior arrangements with them, you can spend a day reading there. You might not want to tell them exactly what you are after. Binksternet (talk) 23:09, 21 March 2014 (UTC)[reply]

Agreed. One person's opinion doesn't count for much. Dolby B's defenders suggested that reducing background his made the sound subjectively less-bright -- which is why I tested without a tape recorder in the path. It isn't practical to visit SF, and I have no idea where I would start searching. (I just did a quick Googling, and found the only references to Dolby B dulling the sound were related to incorrect setup -- which was common.) WilliamSommerwerck (talk) 13:50, 22 March 2014 (UTC)[reply]

Yes, Paul White wrote in 1997's The Sound On Sound Book of Home Recording Made Easy that "Dolby B is often accused of sounding dull on domestic hi-fi cassette decks, but I suspect this is largely due to poor machine alignment or a failure to both record and play back using Dolby B." My own experience of dull sound is from the alignment of the recorded cassette being a little bit different than the alignment of the playback deck, especially with Dolby C which was more finicky. This is supported by a 1994 review in Stereo Review magazine which said "All too often, response or azimuth variations between decks cause the Dolby systems to magnify or dull the highs..." I don't know the author or article name.

Getting back to your experiment, I don't think I've ever read a review of Dolby B in which the reviewer listened to a purely electrical signal path, without transduction to magnetic tape. Binksternet (talk) 17:24, 22 March 2014 (UTC)[reply]

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The description of Dolby C behaviour is entirely wrong. It has never been the same as two Dolby B chips 'bolted together' in terms of behaviour as the current description implies. I'd noticed this description being used all over the Internet and wondered where the misinformation was coming from. It would appear as though this Wiki article may be the source. I will attempt to rewrite this in a week or so unless anyone else has any objections. Gruntsplat (talk) 13:16, 14 December 2016 (UTC)[reply]

EDIT: Scrub that. I've just been issued a warning for not providing a reference to a minor edit I made that was an addition to someone else's accepted content where they'd provided no reference either. If one contributor is expected to provide a reference whilst another isn't, this clearly leads to biased content, so I have no interest in further involvement. Hopefully someone else will look at the linked datasheet and provide the necessary complete rewrite including a brief description of spectral skewing.Gruntsplat (talk) 17:16, 15 December 2016 (UTC)[reply]

Gruntsplat, I do hope you decide to stay and help out on this article. Sometimes valid edits are reverted, and while it's unfortunate it shouldn't turn you completely off from Wikipedia. You clearly know what is right and wrong with this article, so if you leave it will be one fewer person who can accurately update/change/fix/etc it. I'm happy to provide input and/or advice proceeding forward; if you have a question just ping me using {{u|Primefac}}. The first key is definitely finding sourcing for this stuff, which may be difficult if there is as much misinformation spreading as you claim (which I believe). Anyway, please give it a think. Primefac (talk) 17:42, 15 December 2016 (UTC)[reply]

Gruntsplat Concur with Primefac. Please stay. Allow me to mention that a lot of long-standing content on WP got there before we had more strict attention to referencing requirements. So it is not so much a matter of "other editor didn't have to provide refs" but rather "other editor is sort of grandfathered in, but not really." It is still the case btw that any unreferenced content may be challenged and removed (see WP:V), no matter how long it's been there. Jeh (talk) 19:31, 15 December 2016 (UTC)[reply]

I was about to say something about this. Dolby C isn't supposed to be the same as two Dolby B chips together. As well as I remember, Dolby C chips were slow to arrive, so some did it that way. Whether designed, authorized, or whatever by Dolby labs, I don't know. I am pretty sure the first Dolby C deck I bought had the C chip. (and also dbx, which I used more) Gah4 (talk) 20:39, 20 August 2020 (UTC)[reply]

isn't supposed to be... very well said. The decks with B/C NR made of pairs of B ICs (e.g. Akai GX-F91) were certified by Dolby, but they were not fully compatible with decks built around dedicated B/C ICs (different detector arrangements that couldn't be fixed with external components). However, at the very basic level "two Dolby B-style (sic) expanders plus an antisaturation reversal filter" is a fairly decent summary. Retired electrician (talk) 00:16, 13 November 2020 (UTC)[reply]

This article covers an extremely important area of audio technology and it has very poor references. The "How Dolby NR works", "Dolby A", "Dolby C", and the "Dolby B" sections are completely unreferenced, save for the description of Dolby FM in the latter!

As @Gruntsplat: notes above nearly all of the references are going to be found not online, because they predate the Internet. We may however have an "out" in the amazing collection of electronics magazines at http://www.americanradiohistory.com/ It has been OCRd and so is text searchable, although the OCR is often inaccurate, the actual scans are available on the site as well.

n.b.: I will help format references using the cite, etc., templates, if the raw data is provided. Jeh (talk) 20:13, 15 December 2016 (UTC)[reply]

• @Jeh:, purists can nail me for providing the link, but americanradiohistory.org has quite a lot of sources. You don't really need many sources, sometimes a single but very good article is enough. I used to write FAs on Dolby and dbx in ru:, and that was precisely the case - each topic had one easily accessible definitive source (unfortunately, in Russian). I'm sure that if you dig into Elektor and the AES Journal (which americanradiohistory doesn't have), they must have precisely such definitive articles. Retired electrician (talk) 14:05, 30 March 2020 (UTC)[reply]

Understanding this subject would be helped with appropriate graphics- equalization curves, even circuit diagrams.

Public-use graphics might be found in the various patent documents, if no one has the capability to re-do copyrighted drawings. 71.230.16.111 (talk) 22:33, 10 June 2020 (UTC)[reply]

I have updated the article to explain that compression occurs during recording and expansion occurs during playback. However, it may be useful to change the article to use the words Emphasis (telecommunications) and de-emphasis to better explain what is actually happening in Dolby NR. Please look at the article on emphasis and give me your thoughts. — Preceding unsigned comment added by 80.193.55.114 (talk) 22:41, 2 August 2020 (UTC)[reply]