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Dolbly NR. A qquestion I should have asked 30 years ago really.

Discussion in 'audio' started by kennyh, Aug 21, 2014.

  1. kennyh

    kennyh pfm Member

    ........but there was no PFM and the only computer in the house was a Spectrum 48k:D

    So Dolby NR, always an enigma for me.
    It was a switch they started fitting to cassette decks ,and when I bought my first deck with one on board I expected the earth.
    Got it home and blasted out Rebel Rebel by David Bowie and with huge anticipation hit NR. I was mortified, it made David sound as though he was locked in the bathroom with full face helmet on.

    As I went through various cassette decks until I stopped using them in the early nineties I tried all sorts to get this function to work, I had Dolby NR recorded cassettes, I bought stupidly priced metal/chrome tapes but to no avail...........you hit that switch and all goes tits up.

    Anyway I'd forgotton all about that disappointing feature until this week when I rescued a 40 year old tank like Technics cassette deck from oblivion.
    I cleaned its heads as recommended on here and spruced it up to as new condition.
    I then hooked it up to a system and it worked perfectly. Problem was it did sound very muffled and I just put it down to the old cassette media being worse than I remembered.
    I cleaned the heads one more time but it was still muffled.

    Eurika, I then saw its Dolby NR switch set to "ON" and the bad memories came flooding back.
    Switched to "OFF" and the deck bounced into life and sounded very decent indeed.

    So guys, quite serious here. Had I misunderstood what Dolby NR does? Had I not been using it right? Or is it indeed just a switch you flick that makes everything sound shit?

    Thanks.

    PS Keyboard probs whilst typing the title it seems
     
  2. Julf

    Julf Evil brother of Mark V Shaney

    Dolby (B & C) used a compression system that was divided in separate frequency bands. The idea was that if you used it on recording, it would compress and pre-emphasize the music, so that when it was "decoded" on replay, the music would be reduced back to the original, but any tape noise and hiss would be attenuated.

    If you play a Dolby-recorded tape without using the dolby encoder, you get an artificially "enhanced" sound.
     
  3. thebiglebowski

    thebiglebowski pfm Member

    Dolby NR = Patents = Lots of money for Dolby.
     
  4. kennyh

    kennyh pfm Member

    Probably true.
    I'd just to love to know if anyone used it successfully though. As I say on various and many decent specced decks I had way back when, if you pressed or flicked this switch it ruined everything. It must have had some use for people I'd assume, although I never found one.
     
  5. Werner

    Werner pfm Member

    No, not if the deck's record and replay levels were set correctly for the given tape.

    Of course, switching Dolby off would always result in a brighter (but wrong) sound.
     
  6. Stunsworth

    Stunsworth pfm Member

    I used Dolby B all the time. It made music with wide dynamic range listenable.
     
  7. whatsnext

    whatsnext Naimless

    Most people who had Dolby Filtering B and/or C and use it to record then play back found it did what it was designed for. Noise reduction to different extents. I found it could make the sound less hissy for example.

    Did you not read the the Cassette Deck manual were it told you about what each switch was for?

    You seem to have missed the boat on learning what it was for.
     
  8. kennyh

    kennyh pfm Member

    Interesting, many thanks for that.
     
  9. Steven Toy

    Steven Toy L3 Toy

    So David Bowie was singing with a full face helmet on then.
     
  10. kennyh

    kennyh pfm Member

    Cheers guys, just glad they don't put that switch on DACs as well :D

    I'll have a play with the deck over the weekend and see if I can work it out, albeit 30 odd years too late.
     
  11. James

    James Lord of the Erg\o/s

    Cheaper decks don't have a good HF response. When ferric tapes are recorded and played back without Dolby encoding/decoding, it generally sounded flat and dull. Encoding with Dolby but playing back without it artificially enhanced the HF.

    I discovered a proper deck with my first Nakamichi. Even a lowly TDK D cassette sounded pretty close to source when recorded and played back without Dolby, albeit a bit hissy. Encoded and played back with Dolby was marvellous. I'm still kicking myself for selling my Nak.
     
  12. whisky180

    whisky180 pfm Member

    used dolby c with a nakamichi 700zxl, and metal tapes worked absolutely fine
    till the deck went wrong and no-one could fix it
     
  13. Bradders

    Bradders The Pork Chop Express

    Everyone knows you don't do heavy metal in Dubly.
     
  14. Njb

    Njb pfm Member

    My experiences with hifi cassette decks were limited as the introduction of the cd made a cassette less important. My cassette deck was part of a cheap setup and so the failings were masked behind a suspect Dual receiver and a pair of Kef Coda II speakers. My recollections are that I spent a lot of time trying various exotic tapes; ferric, chrome etc. Dolby NR was more successful with the better quality tapes but cheap tapes plus NR was a disaster.
     
  15. krenzler

    krenzler pfm Member

    Dolby was never a good idea unless your tapedeck allowed for proper calibration of any given tape beforehand.
     
  16. Sue Pertwee-Tyr

    Sue Pertwee-Tyr pfm Member

    Cutting a long explanation short, Dolby boosted the treble frequencies during recording, then the Dolby on playback cut them back again, which also had the benefit of cutting back the tape hiss. So if you use Dolby wrongly, you'll mess up the frequency response of the playback.

    Playing back a non-Dolby using Dolby will sound dull, playing back a Dolby cassette without using Dolby will sound shrill.

    A short, simplistic user-guide:

    If you're recording onto cassette, you need to select Dolby when recording and also when playing back. If you didn't use Dolby when recording, don't use it on playback either.

    If you're playing back a pre-recorded cassette, if it was recorded using Dolby, you need to select Dolby again. If it wasn't, you don't select it.

    Most pre-recorded cassettes used Dolby 'B' - make sure you select the correct option for whatever treatment was applied to the cassette when recording. Later or more upmarket models had a Dolby 'C' option. Don't mix and match.

    Hope this helps.
     
  17. martin dawson

    martin dawson pfm Member

    I've just had my Nakamichi 581 and NR200 noise reduction unit serviced by John Chinnock the NR200 has Dolby B & C. He has 40 years experience on working on hi end audio.
    I've got my 2 units up for sale as now my new pre hasn't the facility for a tape deck. So PM me if your looking for a high end Nakamichi cassette deck.

    John number is 01883 743402

    He's based in Godstone Surrey

    Regards,

    Martin
     
  18. Julf

    Julf Evil brother of Mark V Shaney

    That is somewhat over-simplified.

    That, on the other hand, is spot on.
     
  19. Michael J

    Michael J pfm Member

    Now then, Dolby S...
     
  20. Zombie

    Zombie pfm Member

    Maybe you should demag the heads too.
     

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