[Tig] dolby A

Philip Mendelson pmendelson
Thu Aug 8 19:55:15 BST 2002

I'm searching back into my audio past.
Beta SP uses, I think Dolby C (maybe it's B??) on its LINEAR tracks.  Those
codecs are not compatible with Dolby A, which is a 4 band complementary
process. To make matters worse, an undecoded Dolby A signal into a Beta SP
will then be encoded AGAIN in the Beta SP's format.  The only thing the Beta
SP playback will decode would be the complement of its own Dolby encode.
The original Dolby A encode profile will still be there, and most likely in
a mangled, clipped at the top end, form.  Bad idea.
Best to either decode Dolby A on the way in to the Beta SP, or use the AFM
tracks and decode Dolby A on the way out.


-----Original Message-----
From: Rob Lingelbach [mailto:robling at ucla.edu]
Sent: Thursday, August 08, 2002 11:45 AM
To: tig at emsh.calarts.edu
Subject: Re: [Tig] dolby A

On Thu, Aug 08, 2002 at 11:36:33AM -0700, Potter, Stephen wrote:
> Dolby A can be transferred without decode-re-encode like you describe
provided that the levels are perfectly matched between the machines and
reference tones are transferred from the original source to the copy. The
copy must be decoded using the reference tones transferred from the original
source. Otherwise mistracking in the decoder from the copy can occur and be
audible in the form of "pumping" and frequency response errors. 

thank you Stephen.  In my case I need to make some dubs and I
think it would be better for me to decode the Dolby A.  Does
anyone know of any Dolby A decoders available?

Rob Lingelbach   Senior Colorist, UCLA Film and Television Archive
robling at ucla.edu      http://www.alegria.com       rob at alegria.com

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