RE: Dead FM Broadcasting Technologies

[Garrett Wollman <wollman@lcs.mit.edu>]

<<On Fri, 29 Nov 2002 16:01:21 -0500, "Larry Lovering" <larry.lovering@cox.net> said:

> It's been a long time, but I believe the premise was to eliminate or reduce
> noise, making a quieter signal at greater differences.

The Dolby B system for audiotape worked like this:

1) Boost the high-frequency range (where tape hiss is most noticeable)
of the original source by a few dB.

2) On playback, attenuate the same range by the same amount.  The
noise, which (being a playback artifact) was never amplified, drops
down to inaudible levels.

That was the theory, anyhow.  In practice, it didn't always work so
well.  Later came Dolby C and Dolby S noise-reduction mechanisms,
neither of which gained much popularity.  I think that the patent on
``B'' expired just in time for digital recording to take over and
introduce other sources of noise that are (by design) less
perceptible.

-GAWollman