Dolby vs. pre-Dolby

Dolby A?
A Dolby noise-reduction system, or Dolby NR, is one of a series of noise reduction systems developed by Dolby Laboratories for use in analog audio tape recording. The first was Dolby A, a professional broadband noise reduction system for recording studios in 1965, but the best-known is Dolby B (introduced in 1968), a sliding band system for the consumer market, which helped make high fidelity practical on cassette tapes, which used a relatively noisy tape size and speed. It is common on high fidelity stereo tape player…

I’m speaking of analog LP’s produced by record companies in the late ‘50’s and early ‘60’s whose tapes were recorded NOT USING the Dolby A process. which had not yet been invented. And those master tapes were often used in the making of modern CDS.


Cleeds— I think your referring to the modern use of Dolby..

yogiboy == You’re exactly right, but your not addressing what I’m talking about.

What I’m talking about is a real phenomenon that many classical music listeners and others have heard and commented on.  The early pre-Dolby recordings do have a different tonal signature to those made with Dolby.
(When I say recordings of course I’m referring to the master tapes from which the records are made. Let’s not quibble over terminology.)

rvpiano

I’m speaking of analog LP’s produced by record companies in the late ‘50’s and early ‘60’s whose tapes were recorded NOT USING the Dolby A process. which had not yet been invented. And those master tapes were often used in the making of modern CDS.

How would you know which original recordings from the 60s were made with Dolby 'A', and which ones were made without any NR, or were made using a competing compression/expansion system?

As the 60s evolved, multitrack recording became the norm, so that may explain the difference you hear in SQ between the decades.

In any event, none of the Dolby circuits (A, B, C, SR ...) work by "cutting off of the highest frequencies" which are then "electronically replaced."

Hi RVPiano ...

I think I can help you here in a way few other A’goners can. :) I used to work in motion picture sound, and Dolby-A was the noise reduction system used for Dolby Surround. I’ve taken those cards apart, and reverse engineered other bits of Dolby gear from the purely analog era.

I wouldn’t call Dolby audiophiles at all, certainly not back then. They were into effects, and noise and distortion was not high on their agenda to prevent, let alone "microdynamics" or anything close to that. While I believe the idea behind Dolby-A was a good one, to compress high frequency content so it would put less of a strain on tape, and later film, they always implemented their circuits with a huge amount of parts without particular care for anything besides the main goal. They also weren’t very quick to update their products with modern integrated parts which would have given them lower noise, lower distortion results for less cash. Their product cycles lasted a good long time.  Even using purely analog parts, Dolby A would be absolutely trivial to implement today with a handful of IC's, but back then was an electronics store of discrete parts.

We’d have to get a hold of those cards, of course, and attempt an encoding and decoding cycle to see exactly what was going on, but in general, based on the circuits I got to see and the performance I measured in the pro gear, I’d say it’s most likely that the problem wasn’t the idea of Dolby-A but the way Dolby would implement their circuits, going all the way back to the power supplies.

There were a number of poor choices in their film gear, which absolutely left too much noise and blurred too much detail which was in the tracks, so I can easily see how this could have been in the tape recording products.

While we can implement Dolby-A decoding digitally today and spare ourselves some of these problems, we can’t go backwards in time and remove the original encoding and what that must have done to the sound.

Best,


Erik