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What is Dolby Noise Reduction? Dolby's Humble Beginning technology connections

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In this video we discuss the Dolby Noise Reduction systems found in consumer cassettes decks and how they work. Though technically very simple, Dolby B noise reduction provides a very effective means of reducing audible tape noise, and was ubiquitous throughout the cassette’s life.

Dolby noise reduction was such an important part of their legacy that the company still pays homage to it in their logo. The “D”s in the Dolby Double D logo are really the shape of audio tape heads.

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Hypnothis by Kevin MacLeod is licensed under a Creative Commons Attribution license (
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What is Dolby Noise Reduction? Dolby's Humble Beginning

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45 thoughts on “What is Dolby Noise Reduction? Dolby's Humble Beginning technology connections”

  1. Frate, de unde ai gasit camasa aia? Nu se mai poarta de 15 ani. Acum se poarta slim (cambrat). Esti tanar. Poartat haine pt varsta ta… daca vrei sa dai bine pe sticla (ecran). Arati ca si cum te-ai imbracat cu hainele bunicului. Un inginer trebuie sa stie pe ce lume traieste. Sa aiba simtul realitatii.

  2. I want to record this video on to VHS and mail it to my 90s self to watch so I would have known what all those weird options were for on my nice tape deck.

  3. It always got rid of the higher notes, and I never use it. It was shit. Yet another goo…ish scam. Sure, believe what you want. Oh how about Dolby C ? Crap shit of the past. Only idiots still use this crap.

  4. A simpler form of this, pre-emphasis, was also commonly used on LPs to reduce high frequency noise. You could probably do multiple videos on the format wars around LP equalization curves and pre-emphasis, but it eventually settled out with a standardized "RIAA curve". CD later included a pre-emphasis option as a workaround for high frequency quantization noise caused by early encoders and poor playback equipment, but it was inconsistently implemented and rarely used. Speaking of which, if you haven't done a video on HDCD and how it revolutionized CD premastering, that's definitely a worthy topic.

  5. Dolby invariably sounded horrible, cutting off a lot of the sounds between transients and sometimes giving a weird muffled underwater vibe depending on the dynamics of the music and the volume at any particular time. Often it was more comfortable just to reduce the treble to compensate for the boosted high frequencies on a Dolby encoded cassette. In the days of Walkmans there was never a completely satisfactory sound quality from cassettes in my experience

  6. Noise reduction is also why some old recordings with low budget recording followed by low budget digital transfers sound terrible. A lot of old bluegrass (and I assume other niche musical styles) was recorded without any noise reduction reduction, but the digital "remasters" are sloppy with the stuff. I often just boost the treble on them until I hear enough hiss to make the music sound right. I wish there were better tape transfers of a lot of these classic albums. Of course there are also occasionally albums transferred without the RIAA curve. I wish Dolby would write a software plug in to add/remove noise reduction in a daw so some of these old transfers could be fixed.

  7. Although your explanation was pretty well spot on, the reality of living with cassette tapes was quite different at the time. Dolby wasn't by any means ubiquitous in all playback equipment, and even when it was there it was largely ignored. This might have been because the end result was never really what you would have expected from an untouched recording. Many people, myself included, just ignored the Dolby to what extent was possible. Some friends and I actually did some digging, and found that the whole noise reduction process was highly dependent on the tape itself, as well as the calibration of the electronics. What we found was that the best you could expect on any given playback machine was for the response curve to be more or less correct only for one oxide formulation. In later days, tape quality improved dramatically, and so did output level. This meant that because of the much higher output for the same recording level, the noise floor was automatically lowered to produce much better noise performance without using the Dolby at all than it was previously with it. The upshot is that millions of recordings were made with built-in distortion, which couldn't really be fixed. Living with this situation caused a smouldering resentment among those who were sufficiently aware, although much of the listening public had no idea anything was wrong, and anyway, so much of the commonly used equipment either didn't have Dolby or the user just ignored it. In later days, tape formulation had improved so much that an unadulterated recording was almost indistinguishable from a CD. The end result was that we got decades of ruined cassette recordings for no good reason. Dolby made tons of money and ended up in the undeserved position of being the default audio codec when the DVD came along.

    Taking everything into account, including hindsight, having cassette tapes as your normal means of consuming music was a decidedly disappointing experience. So, the Dolby Distortion was only a relatively small component of the unhappy situation. People today have no idea how lucky they are.

  8. When I got a my first cassette player with Dolby noise reduction I was pretty sure it was the same as lowering the treble . Furthermore your S alliteration was hotter than a urinary tract infection . Thanks for some sweet ass content .

  9. Great content … but the combination of the white shirt and naïve use of chroma key, made the red watch, microphone, and peculiar bow-tie very distracting to watch. Listening to this rather than watching, is the best way to get the most out of this posting.

  10. Dolby A didn't go over too well because many people held the opinion that it tended to give things a "harsh" sound. Part of this, I think, is probably a misunderstanding of how to utilize the system. I admit that as a young kid, I never liked the sound of Dolby but then I never had quality equipment to listen on and since "brighter" tends to sound better in many cases, I only rarely used my boom box's Dolby processor, not fully comprehending what it was trying to do.

    One fun fact is that the Dolby boost did some interesting things that engineers sometimes decided to take advantage of during mix down. So as a way to give lift to some sounds, they'd be run through the Dolby boost and then mixed into the recording as they were.

    Audio SNR is still an issue but mostly only within the recording studio and there the issue is microphone sensitivity vs the source relative to ambient noise and self-noise from any outboard equipment processing the sound. (Like turning a speaker way up with no signal. The "hissing" sound is the self-noise of the amplifier.)

  11. Not sure if you have already done this and I have somehow missed it, but I would like to see new microphones versus older microphones (the ones they use to look good in films of a certain age!!!) Love your stuff, Thank you

  12. Unfortunately, the explanation in this presentation is flawed in a way that cannot go uncorrected.
    The author conflates spectral recording pre-emphasis and reproducing de-emphasis with “companding” when actually they are two different but complementary processes.
    Companding (which Ray Dolby did not invent, but improved upon) is not spectral – or frequency related – but purely amplitude encoding. By compressing the signal in amplitude mode, we are able to place the entire signal at a level well above the noise floor of the tape hiss, then re-expand the signal on reproduction to relegate the tape noise to an almost inaudible level. Dolby improved upon this by introducing a four—band “sliding band” differentiator, which did allow different spectral components to receive differing compression and subsequent expansion ratios. High-frequency pre-emphasis in recording, and complimentary de-emphasis in reproduction are complimentary techniques, but in no way fundamental to the companding process, as this author appears to suggest.
    In an interesting anecdote, Dolby (who began his illustrious career developing tape-based video recorders for Ampex) applied this A-Type noise reduction to optical motion picture film, to develop Dolby Stereo, however it proved relatively inefficacious in reducing the impulse noise induced by dust particles on the optical soundtracks of film, and the Dolby “magic” was really never perceived beyond the Hollywood screening rooms that received pristine film prints, straight from the lab. Improvement would await the introduction of Dolby’s “SR” (Spectral Recording) process, which did solve the problem, but alas by the time this was launched Kodak and ORC had already launched CDS – the first truly digital sound format for motion pictures, which was quickly followed by the dual-support DTS format, both of which blew Dolby-SR out of the water before it even hit the theatres – forcing Dolby to precipitously develop the technically inferior SR-D format just to remain in the game at all.

  13. Then, when the early CDs were created, the producers of them often didn't remaster the audio for CDs, and they used that same, heavily treble-boosted master for many of the CDs. Thus, the 1990s had tons of excessive treble, which made people want to boost the base more. The CDs even tended to have markings to indicate what stages were done digitally or as analog. That gave people a bit of a hint as to whether they were paying for a product that deserved to charge the normal CD price, or if it was a minimal effort to reuse a master with no alteration and overcharge everyone as if it was done from scratch.

    But I will say it's a good explanation of dubly…I mean Dolby.

  14. Dolby B only operated in the high frequency range. As most of the noticeable tape noise was in this range, it allowed the system to still be reasonably effective.

  15. "The Dolby chip inside the cassette player…" No, my friend, true Dolby NR was implemented with discrete transistors. Today, you systematically reach for the word "chip" to represent electronic circuits. In 1974, analog (audio) integrated circuits, although very complex and useful, were still in their infancy, and did not have as good a noise performance as discrete transistors. I have 2 cassette decks from the 1970' + 80's. A Sansui, and a Pioneer ( the Pioneer with the Omega tuning fork logo, not the new Chinese Pioneer crapany). Both have discrete transistor circuitry exclusively on the PC boards ( and it's a LOT of circuitry). Integrated circuits that could surpass discrete performance in noise and distortion didn't come to market until after 2000. And by then, virtually all audio component manufacturers had moved over to digital due to digital's inherent ability to reduce/remove noise and distortion, as well as to the efficiency and low cost of automated surface-mount PCB fabrication, virtually all of which is done in China.

  16. Maybe it's because I was a kid when Dolby noise reduction became common, and because kids love treble, but I never liked how music sounded with Dolby turned on. To me the hiss in the background of a cassette was a bit like the paper on an easel before the paint/music was added to it. The hiss sort of provided a reference point to let you know how intense the sounds of some songs were compared to others. Or at least that's how my adolescent brain analyzed it. I probably just wanted more treble.

  17. RIAA Equalization for vinyl recordings is a similar process, boosting high frequencies during recording to minimize treble noise while cutting low frequencies to keep the grooves narrow for maximum play time on a disc.

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