dolby b and c

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dolby b and c

Permanent link to this post Posted by misja » Fri Jul 23, 2010 9:22 pm

hi,
i want to use audacity to digitise my audio cassettes. i recorded them in the past on a nakamichi cr-3e deck with dolby-c enabled.
the nakamichi is not working any more sadly and as all the tapes are over 10 years old i do not expect incredible high quality after digitising but want to do it as good as possible.
i want to use a ion tape express which is a cheap player with usb interface but this player has no provisions to set the tape and dolby characteristics.
has anyone ever tried to make a filter to compensate for things like this? i do realise that dolby-c is more complicated then a simple filter but maybe it is possible to do some improvements or do i need to search for a working deck with dolby-c?
any help and suggestions welcome,
thanks.
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Re: dolby b and c

Permanent link to this post Posted by billw58 » Fri Jul 23, 2010 11:50 pm

Find a good used deck that has Dolby C. The Dolby NR system uses dynamic compression of the high frequencies.

http://en.wikipedia.org/wiki/Dolby_nois ... ion_system

I can't think of a straightforward way of implementing Dolby decode in Audacity.

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Re: dolby b and c

Permanent link to this post Posted by Trebor » Sat Jul 24, 2010 1:15 am

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Re: dolby b and c

Permanent link to this post Posted by steve » Sat Jul 24, 2010 1:23 am

Unlike Dolby B, Dolby C is in my experience much more forgiving of playback without Dolby decoding.
For Dolby B the encoding/decoding was heavily biased on the "pre-emphasis/de-emphasis" of high frequencies, (but also dependant on the level). The result is that playback without decoding always sounds a bit wrong. With Dolby C, the bias seems to be more on the compression/decompression side, (but also frequency dependant). The result (in my experience) is that playback without decoding sounds a bit "flat" in terms of dynamics, and a bit overly bright, but not so "wrong". Tapes tend to loose top end with age, and the noise floor gradually rises, so old tapes that have been recorded with Dolby C may actually sound better if they are not decoded. If you know anyone that has a reasonable quality cassette playe it would be worth testing some of your tapes to see how they sound (after 10 years of ageing) with vs. without Dolby C. This will depend in part on the type/quality of tape that was used. (I have some recordings made with Dolby S on expensive metal tape that now sound terrible no matter what I play them on :( )

Unfortunately with tape, high quality recording or playback cannot be done cheaply. The materials and manufacturing quality of components such as the tape heads make a big difference to the sound quality and cassette players of the quality of some of the old Nakamichi decks are just not available these days at any price.
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Re: dolby b and c

Permanent link to this post Posted by misja » Wed Jul 28, 2010 2:16 pm

thanks for the replies to my question,

i have not yet been able to compare with or without dolby c playback as i do not have access to a working deck with dolby c but i did a few loads into audacity ignoring the dolby c and i think i agree with steve that it actually sound reasonable good.

i will have to do dolby b tapes too and they might be more problematic but on the other hand it might be easier to find a dolby b player.

thanks so far.

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Re: dolby b and c

Permanent link to this post Posted by whomper » Wed Jul 28, 2010 4:55 pm

not likely to find a dolby cassette these days

my deck died
used one without the feature and just copied the tapes
sounded good
if they sound off then tweak the highs with eq to suit

could be my ears
but i never really heard a difference with it in/out on my deck
(maybe it was a switch that did nothing but toggle to fool users)

on the other hand
i was one of the few people at work who could hear the whine
on the crts connected to the computer (about 15Kcps)

try copying the tapes with anything
before you obsess about finding a dolby box to use
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Re: dolby b and c

Permanent link to this post Posted by steve » Wed Jul 28, 2010 11:23 pm

whomper wrote:not likely to find a dolby cassette these days

See here: http://www.google.com/products?q=cassette%20deck

If a person is unable to distinguish the difference between playback with/without Dolby B, they have a major problem, either with their hearing or with their equipment or their listening environment.
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Re: dolby b and c

Permanent link to this post Posted by whomper » Thu Jul 29, 2010 1:58 am

they *are* available
but most of the cassette gear does not have dolby
or a lot of other features these days

i still have my outboard dolby boxes should i care enough to use them

i am not a golden eared stereophile type that thinks something that sounds different means it sounds better

i listen for enjoyment
either i like it or i dont
and i dont obsess if it sounds different only if it sounds bad
if it sounds good i dont even think about other issues like dolby
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Re: dolby b and c

Permanent link to this post Posted by billw58 » Thu Jul 29, 2010 2:01 am

misja wrote:i have not yet been able to compare with or without dolby c playback as i do not have access to a working deck with dolby c but i did a few loads into audacity ignoring the dolby c and i think i agree with steve that it actually sound reasonable good.


I'm afraid I disagree with Steve. Dolby C is much more aggressive than Dobly B (it is essentially two Dolby B stages in series, with some tweaks), and playback of Dolby C encoded tapes without Dolby C decoding will result is audible pumping of the high frequencies. The transfer will sound artificially "bright", and may sound "better", but will become fatiguing to listen to for extended periods.

Misja, you don't say where in the world you are, but it would be worth your while, if possible, to check out eBay, Craigslist and Kijiji for a good used deck. You may have to do some research or contact the seller to find out if the deck has Dolby C. This is your one chance to do these transfers and you might as well do the best job you can.

This article on the Audacity wiki has lots of good information on recording from cassette: http://wiki.audacityteam.org/wiki/Recor ... m_Cassette

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Re: dolby b and c

Permanent link to this post Posted by steve » Thu Jul 29, 2010 2:23 am

billw58 wrote:I'm afraid I disagree with Steve.... The transfer will sound artificially "bright", and may sound "better", but will become fatiguing to listen to for extended periods.

That's OK Bill, we're in the area of subjective appraisal so I would expect different opinions :) but to be clear, I was speaking specifically with reference to very old tapes. With new / good condition tapes recorded with Dolby C I would agree with you entirely.

BTW, most of the search results from the previous Google link were cassette players with both Dolby B and Dolby C.
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