Dolby noise reduction

September 5, 2022
 by Paul McGowan

Ray Dolby was a pioneering engineer.

While many folks would recognize the name as associated with multi-channel home theater—Dolby Atmos for example—the beginnings of Dolby were an attempt to reduce noise in tape recorders.

Tape recorders have hiss. It’s just part and parcel of their process of magnetizing the metal particles on plastic strips of tape.

What Ray Dolby did to reduce that tape hiss was pretty clever.

Dolby A (the first iteration of the Dolby noise reduction system) boosted the volume level of incoming audio when that audio signal was below a certain loudness threshold. On playback, the system reduced the level back again (signal plus noise), thus lowering noise. This system of pre-emphasis (as it was known) is quite similar to how more musical information is pressed into a vinyl record through the RIAA pre-equalization (though the RIAA curve is constant while Dolby is dynamic).

The reduction of tape hiss using Dolby was rather dramatic with up to 10dB of improvement.

The furor over sound quality was equally dramatic.

As with everything in the audio chain, when you manipulate the audio path as did Ray Dolby you change the sound quality. And according to many not for the better.

Soon there were battle lines drawn and the various camps gathered steam. One crowd did not wish their audio signal to be modified and were alright tolerating the tape hiss. The other camp either didn’t/couldn’t hear the differences or didn’t care, preferring the quiet of music without hiss.

When digital came around there was no longer any hiss to eliminate. Dolby Labs (as it had become known) pivoted from noise reduction to promoting multi-channel audio and the rest, as they say, is history.

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29 comments on “Dolby noise reduction”

  1. If a hard core audiophile never ever would accept any kind of manipulation of the audio path vinyl would be a no go and only direct master tape recordings (no mixing, no mastering) would be allowed. Indeed, mixing and mastering can do a lot of harm when made by non-experienced sound engineers. And in the end the enduser defines the biggest manipulation of the perceived sound quality by adding the footprints of his individual listening room acoustics and his more or less colored loudspeakers creating all kind of time smear from different drivers.

  2. Some even today digitize/declick their vinyl for getting rid of some dust noise, but suck out any life and ambiance instead (unless as in your Dolby example their setup isn’t capable of revealing the difference). This is something I will never get, especially when it concerns quite ordinary records, available without those extra losses from streaming services.

    Dolby I think was partly necessary in cassette decks, but nowhere else really. The bit of hiss was just another artifact, playing no dramatic role in overall sound quality, but sold to us dumb audio customers as an essential improvement, while its downsides were kept quiet for the most part.

    When as you mentioned, early digital came, it was certainly much better technically than a commercial Dolby cassette, but compared to the recordings on LP, it mostly also just removed some secondary artifacts but not rarely lost much more by at the time inferior transfers and or overly compressed masterings to the silver discs.

    I’d say audio customers are more frequently used to this than to groundbreaking innovations.

  3. Apparently Dolby’s first break with his noise reduction technology was for Stanley Kubrick on the soundtrack of A Clockwork Orange in 1971. SK was a great technological innovator. He had a house in Elstree, a boring small satellite town just north of London, from where he made all his films from the early 1960s until his death. Elstree just happens to have a big film studio (used extensively by him and the likes of Hitchcock, Spielberg and George Lucas), where my grandfather often worked as a set designer. I watched Full Metal Jacket last night, for which he turned an old factory in East London into a pretty realistic version of Vietnam. Apparently Ray Dolby had just set up business in London, having done his doctorate at Cambridge. Dolby noise reduction was used more extensively on SK’s next film (and my favourite) Barry Lyndon. I suspect Dolby NR would have been well suited to SK’s penchant for Baroque music, used in both of those films, Clockwork Orange’s main theme being Handel’s music for the funeral of Queen Mary, ironically the second performance being at his own funeral as he died a few months later.

    I read that the Dolby family have given something over $100m for a new national Physics laboratory as part of the rebuilt Cavendish Laboratory, where he did his doctorate, due to open next year. https://www.phy.cam.ac.uk/rdc
    The Cavendish is probably the most famous physics lab in the world, the first professor being Maxwell, and where the electron, neutron and DNA were discovered and the first controlled fusion carried out. So the Dolby name lives on for many years to come.

    What a great guy!

      1. … except for the silly mistake, it was Purcell who wrote the funeral music for Queen Mary and, inadvertently, himself, used in A Clockwork Orange, Handel Vivaldi, Back and others used in Barry Lyndon. Wikipedia hoped on a couple of things!

        The thing was, Dolby had rapid and widespread success in the film industry and digital recording actually started early in Dolby’s career. Barry Lyndon came out in 1975, I think the same year as the first digitally recorded albums were released by Denon.

  4. The Dire Straits album – ‘Love Over Gold’ (AAD) had so much tape hiss in the background of the music that I nearly cried every time that I tried to listen to it back in 1982/83.
    It reminded me of the annoying surface noise that my vinyl collection was plagued with, but this was on
    a CD, fGs!
    I hardly ever listened to it because the audible tape hiss just ruined it for me.
    I often imagined Mark Knopfler shooting the recording engineer dead with Dirty Harry’s 44 magnum.
    Thankfully a (re)mastering magician by the name of Bob Ludwig came along & with his magic wand managed to remove approximately 85% of the destructive tape hiss without ruining the music.
    Needless to remind everyone that the next Dire Straits album ‘Brothers In Arms’ was a ‘DDD’ release.

    In the late 70’s/early 80’s it was all about TDK-MA90 cassettes & Dolby ‘C’ but there was no way of getting rid of that vinyl surface noise.

    1. I’m a little younger than you at 41, but I shared the love and appreciation of Dolby C and those beautiful Metal TDK tapes! Fortunately they started to go on sale in 5 and 10 packs at Best Buy in the early 90s, so it was affordable on my paper route & shoe-shining salary.

  5. One thing that frequently puzzles me…. Why is it that music in a movie soundtrack frequently sounds better than it’s 2 channel format counterpart? This happens frequently, particularly on DTS or DTSX tracks, which I find superior to their Dolby counterparts.

    Is it because I’m listening differently, because more intelligent bass management is used, because of the extra channels, because of the format or some other reason? I was watching Jurassic Park Dominion yesterday and was really impressed with the orchestral part of the soundtrack.

    I think it has something to do with the enveloping sound of a mutli-channel experience. I recently picked up The 4K Atmos disc of “Eric Clapton: Lady in the Balcony”, which is an acoustic session he recorded in a church during the pandemic. He recorded it in Atmos, but it’s done correctly highlighting room ambiance vs. sounds coming from everywhere. I flipped between the 2 channel and Atmos sound track, as the disc has both. The 2 channel is unlistenable once you hear it in Atmos. However, the opposite is true when it it’s just sounds coming from everywhere.

    1. I hear you Reed.
      Just last week I was watching Guy Ritchie’s 2015 film ‘The Man from U.N.C.L.E.’ at home
      & I was blown away by the amazing clarity, mix & ‘snap’ of the soundtrack…goosebumps!

    2. If you look it up, the thing about JP Dominion is that, because of Covid19 issues it was recorded with a socially distanced orchestra using Abbey Road Studios 1 and 2 at the same time. That’s a huge amount of recording space. The mix was done in California.

  6. My first cassette deck of note was an Aiwa 6900. Being 3 head you could mess about with the eq and toggle between source and recorded. I personally didn’t like the hiss so used metal tapes and Dolby b, it never really got rid of the hiss but was largely music depending. Later we got c but hey, you have remember where we were in the 80s. I know it’s contentious but I so miss the vu meters!

  7. I never like or used Dolby. It seems to cut off the high end to my ears. I think dbx did it better with tape and vinyl. Dbx vinyl LPs sound amazing to me. If you never heard one you can’t hear the needle, drop or trial in/out. Home recording with dbx gave you a lot of options. The big drawback of dbx is you need their equipment to playback and record. As was not the case for Dolby so it came down to convenance and $$$.

    1. At least Dolby actually did something beneficial to the sound in lowering hiss on a well calibrated deck. According to many, the same can’t be said for MQA…LOL…Even Bob Carver said in a white paper only a bat might tell a very slight difference…

  8. To Dolby, or not to Dolby…that was the question…
    And if your system was somewhat lacking in top end, record with Dolby and play back with Dolby off for an extra treble boost!

    The 80s… It was buy an album, the virginal play was always recording it to cassette (I always preferred Maxell metal). That way, you got the least amount of #^&% record noise but with a new extra bit of added bonusssssssssssssssssss. Oh yes, the struggle was real. I’m pretty certain I wept joyously for weeks when digital arrived. Two noises killed off with one digital stone. Love Over Gold, The Color Of Spring & Brother Where You Bound were my pre-planned and severely anticipated first cd purchases. Insert more tears of joy. DIGITAL! This clean quiet dynamic noise free media would surely be the end of the turntable!! Ok, it’s hard to get thru the day without a jesticular poke at vinylheads… 😉

    ‘You might be an audiophile if’ secret reveal #7:
    My first year of university I got a $1800 student loan and a $1000 grant (Apparently I USED to be smrt unuff to qualify for free bonus $$$…). The grant was a cheque. A CHEQUE!! Idjuts. You simply do NOT give a cheque to a emerging broke wide eyed audiophile in training. The TOTL Pioneer CT-F1250 cassette deck was $999.99. Coincidence?? Yeah, I didn’t think so either.
    Sure ‘nuff, 40 years later, I still have that silver faced blue metered magnificent sound duplicating rack mount marvel of sound engineering beauty. That was the last year UBC entrusted grants to moro…idio….imbeci…students; they were subsequently applied directly to the debt. I’m certain local used car, audio, clothing, sports equipment and alcohol sales took a catastrophic hit over that.
    Dolby (and a life-long path of further misguided audio purchases) taught to me thru the benefits of higher edumacation.

    1. that was a good deck. Back in the Day, I ran into J Gordon Holt at a stereophile show.
      He was playing NICE DOLBY -S tapes from his Home/concert recordings. As well as Copies of CD’s. His comment was Most can’t hear the difference. Of course those are audiophile ‘fightin words’. I listened in show conditions…couldn’t tell. Heck I thought DAT was pretty good back then….so, grain of salt here.

  9. My neighbor, Dagmar Dolby(Ray died a few years ago) , bought my 30 year personal residence a year ago. I had a 40W by 50L living room with a 25ft. ceiling and log walls to prevent “slap” for sound. I was a recording enginer for the San Francisco Conservetory of music(graduates include Issac Stern, Yehudi Menuin and John Adams). We learned that tape bias permited our tube tape recorders to record 100+ db of dynamic range with no hiss. With an additional output to a Nakamichi with dolby C we had to lower the recording level to prevent overload. Done properly, no hiss. We used a Magnacord and Ampex MR-70. Lots of interesting stories.
    Do you still have my sampler disc?
    Jack Kenny

  10. Dolby made cassettes into the monster format they became. Without Dolby B I wonder if cassettes ever would have been more than for recording interviews and phone messages? Here in 2022 many forget or never knew that at one time tons of pre-recorded cassettes were sold and they were welcomed because they offered easy to use portability and could be played in cars and boomboxes something you couldn’t do with vinyl.

    I’ve read that no one much liked Dolby C because it was more temperamental in the calibration and head alignment of the decks, but later, Dolby S was so good (and could be played back “OK” in Dolby B) that most people couldn’t distinguish the tape from the source, even if that source was CD.

    For an analog format developed in the 1960s that was astounding. Sadly just when it seemed we had the best level of analog cassette recording possible along came lossy mp3 files which were widely adopted in the dial-up Internet days and the quality of music took a downturn that only now the masses are recovering from.

    I still have a few cassette decks with Dolby B and Dolby S and use them some just for fun to record vinyl albums.

    Hats off to Ray Dolby for creating the magic that made all this possible. Much of my youth was spend recording and I loved every minute of it.

      1. Yes indeed. My old Sony KE400S and KE500S decks might not be Nakamichi Dragons but they are still going strong and to me always sounded great. Used them back in the day to “seed” tape trees for Grateful Dead, Phish, and Widespread Panic to help distribute live shows to fans. It was all a labor of love…

  11. I found Dolby Noise Reduction unlistenable. Compansion never tracks. Compression is throwing away information, it can not be re-constructed without losses of transients and other dynamics, inter-modulation distortion and the 800 pound gorilla, TIME DISTORTION. Time distortions are rarely if ever measured, and 99% of speakers listeners are deaf to the universal time and transient distortions of the audio/music business.

    Better magnetic oxide formulations and milling help with tape hiss, but the real answer is wider tracks. Quarter inch half tracks gain 3+dB and wider tape gets above proportionate improvement. There are even 1″ and 2″ half tracks made for mastering machines. (the trade is vertical alignment gets tighter)

    Electronics and heads are also a factor. The Ampex ATR series, Studer Pro decks and even my Sony TC854-4 had better trade-off in SNR and HF response than nearly all consumer decks. The best was esoteric marque Stephens, famous for the 40 track 2″ machines used by Leon Russell and Cars/Queen producer Roy Thomas Baker. These had the same mixed SNR as contemporary 24 track 2″ machines from Ampex, 3M, and MCI. The sweetest multi-track I ever heard was a 16 tack 2″ Stephens. Mics, preamps and studio backgrond noise were louder – and this studio was in a basement in bedrock up Four Mile Canyon in the Rocky Mountains.

  12. I purchased a Dolby stand alone box connected to my reel to reel tape machines. It worked but I soon tired of it because of the breathing you could hear. The background noise went up and down with the dynamics of the music.

    Next I used a Burwin Noise Eliminator. It added about 20db of extra dynamic range but still there was the breathing.
    Lastly in the 1980s I got a dbx box that I still have. With my Crown SX724 and dbx I got some worderful recordings of music in Columbus Ohio. Its interesting becasue my recording buddy had a lot more money then I did so he purchased a Mark Levinson mixer board (back when Mark actually owned his namesake.) and some Shoops and bk microphones. It was heaven.

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