[Mike Rivers[_2_]]

On 12/22/2014 2:14 PM, wrote:
Thanks Mike R, excuse my dyslexia. So the expansion during Dolby NR
in playback of cassette 'pushes down' the noise floor?

No. Forget "noise floor" and think "tape hiss." They're not the same.
Dolby noise reduction does nothing for the noise coming in with the
source, it only affects the noise introduced by the recording process.

The incoming signal is emphasized (high frequency boost) and compressed.
The level coming out of the Dolby processor and actually going to the
tape head is raised to achieve the standard ("Dolby") level of magnetism
on tape. The playback is expanded to restore the dynamic range, the
de-emphasized to bring down the high frequency boost (with some hiss
along with it), and that's what you hear.

Some people liked to listen to an unprocessed Dolby B recording,
particularly in a car, because it's compressed and has some top end
added to it, both of which make it easier to hear the recorded content
in the presence of a high ambient noise level. Not accurately, of
course, but less gets covered up by road noise and screaming kids in the
back seat.

And some people say "Dolby dulls the high end" because they can hear the
de-emphasis taking place when they switch in in when the music is playing.

Dolby B isn't the greatest, but it does what it's supposed to do. Dolby
C does it a little better.

--
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