arsclist Dolby and unintended consequences

["Richard L. Hess" <arclists@xxxxxxxxxxxxxxx>]

Hi,

A couple of weeks ago, Jim Wheeler pointed me to an article by Dave Moulton 
in TV Technology 
http://www.tvtechnology.com/features/Inside-Audio/f-dm-badaudio.shtml that 
addressed some "bad audio" problems related to Dolby noise reduction.

The article specifically addressed Dolby C encoding on Beta video decks. 
According to the article, the early Beta decks had a switch to turn the 
Dolby on and off (much like most cassette recorders). Further, the article 
states that with the advent of BetaSP, that switch was eliminated and 
permanently wired "on."

I'm sending this email out just in case someone doesn't realize that the 
Dolby and dbx noise reduction processes are double-ended and a 
fully-functional unit is required to properly reproduce the encoded tape.

There are no plug-ins to DAW software (to the best of my knowledge) that 
will decode any of these noise reduction systems. You're stuck either with 
the hardware built into the player or with the outboard decoders.

These processes will sometimes magnify errors if the tapes or playback 
machines are not in great condition. In addition, it is possible to have 
defective decoders (don't ask me how I know). In all cases, trust your 
ears. If you think you're hearing a noise reduction problem, try and get to 
the bottom of it sooner rather than later.

Dolby C is built into Sony's Beta decks as well as Panasonic's MII decks. 
Dolby A was optional on 1-inch Type C videotape. I suspect that a few quad 
tapes might have been recorded with Dolby A, and that Dolby A might have 
been used on other formats as well in limited quantities.

As to audio-only recordings, perhaps this would be a good time to just 
mention the different flavors of noise reduction companding that have 
existed. I may even have missed one or two:

  DOLBY
    A-the first studio standard (interrupted tone)
    SR-the second studio standard (noise reference)
    B-the first consumer standard (widely used on cassettes)
         also used on FM broadcasts
    C-the second consumer standard
        also used on some semi-pro multi-tracks and video formats
    S-the third consumer standard (used on some cassettes
        and some semi-pro multi-tracks

  DBX
    I - the pro standard
    II - the consumer standard also used on discs, FM broadcasts,
         and in the stereo TV standard for the difference and pro channels.

  BURWEN
    Although noted for his single-ended noise reduction products
    they also produced for a time a 3:1 linear compander.

  TELEFUNKEN
     C4D ? this was yet another, incompatible, compander system with
     some penetration into Europe.

FYI, I have multiple copies of processors for Dolby A, SR, and B, and dbx 
I, and II. I don't have any for Dolby C (other than on cassette) or Dolby S 
nor the Burwen nor Telefunken systems.

Remember, the metadata on the tape box about the noise processing MIGHT BE 
WRONG. (I've had that happen more than once).

Good luck.

Any questions, please email or post to the list.

Cheers,

Richard

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