Re: arsclist Dolby and unintended consequences

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

At 11:59 PM 06/25/2002 -0700, Mike Richter wrote on the ARSC list:

> I believe Dolby FM used the standard Dolby B but worked on the signal 
> before de-emphasis. That may be the difference Joe thought of. Note that 
> calibration was particularly critical; if the broadcaster did not provide 
> a reference tone regularly and the listener did not use it (in particular, 
> record it with the program), the sound degraded markedly.

Yes, I do recall something about that. I think I modified one of my Dynaco 
FM-5s to have a front panel switch to change the deemphasis. Perhaps it was 
a change from 75 to 25 µs deemphasis pre-Dolby?

It's starting to come back to me. A look in Google confirmed this:

From http://www.dolby.com/company/chronology1970_1979.html

> February 1974
> ·       Dolby FM system combining B-type noise reduction and 25 
> microsecond pre-emphasis demonstrated to Federal Communication Commission 
> (FCC).
>
> June 1974
> ·       25 microsecond Dolby FM broadcasts approved for U.S. by FCC.
>
> August 1975
> ·       100 US stations broadcasting in Dolby FM.
>
> October 1975
> ·       Dolby FM broadcasting approved for Canada by Canadian Department 
> of Communications.



Cheers,

Richard

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