Even though your tapes won’t be damaged if you do this, are
there any benefits of using Dolby B noise reduction on Dolby C and Dolby S
encoded cassette tape audio recordings?
By: Ringo Bones
Fortunately, doing so will not result in a damaged cassette
tape or tape deck, but the practice gained popularity back in the late 1980s
and early 1990s – or whenever time Dolby C and Dolby S encoded prerecorded cassette
tapes became widely available. I mean I even heard of one audiophile back in
1993 praising the sound quality of Gen. H. Norman Schwarzkopf’s spoken word
album after playing a Dolby S encoded cassette copy of on a car stereo that’s
only equipped with a Dolby B noise reduction system. But first, here’s a brief
review of the Dolby C and Dolby S noise reduction systems.
Dolby B reduces tape noise at frequencies starting at 500-Hz
and achieves a noise reduction of 8 to 10 dB while Dolby C starts to work at
150-Hz and above and achieves a noise reduction of 18 to 20 dB, But Dolby S is
a simplified domestic use version of the Dolby SR – a professional signal
processing scheme and not just a mere noise reduction strategy. Dolby S
consists of a number of circuits operating together to reduce tape noise right
across the 20-Hz to 20K-Hz audio band, not just in the high frequencies where
Dolby B and Dolby C operate – and Dolby S will do this with minimum possible
audible intrusion.
But given that doing so – fortunately will not damage both
tape and deck – why is it then that this scheme results in an inexplicably
improved subjective sound quality? Well, it could be the resulting “treble lift”
due to the different playback curve of Dolby B compared to Dolby C and Dolby S
noise reduction systems and the resulting treble lift compensated for the
inherently noisy automotive environment. And the different playback curves of
the various Dolby noise reduction systems also resulted in lifting the
mid-range portion of the audio spectrum that resulted in a vacuum-tube like
warmth in tonality of a solid state car tape deck. Which, unfortunately,
resulted in car stereos – especially those models made by Alpine – target number
one for car break ins. Using Dolby B noise reduction on Dolby C and Dolby S
encoded cassettes also benefitted Walkman / portable cassette tape players
during the late 1980s and early 1990s because most affordable Walkman models at
the time are only Dolby B noise reduction capable - all of this proving Philip's claims that the Dolby C and Dolby S noise reduction systems are "backwards compatible".
