At 7:48 AM -0700 4/25/02, Paul Gibian wrote:
>Sorry for the NDC, I've always been curious about Dolby decoding and several
>fellow travelers are talking about how this might be done for Dead shows.
>Could someone send a link to or a "not-to-technical" explanation of the
>decoding of cassettes with Dolby? My basic question: is Dolby decoding done
>in analog or the digital realm?
It may be possible to do it in the digital realm -- writing an
algorithm for the Dolby B curve wouldn't be all that hard -- but the
way it was done was to pre-emphasize certain frequencies (where the
hiss occurs) as you record and then de-emphasizing those same
frequencies on playback, reducing the added hiss along with the
affected audio frequencies.
It was calibration-dependent, which is why recordings made on one
deck might not have been properly decoded when played back on
another. Ideally, there would be a Dolby level tone on the tape so
you can calibrate playback. But most cassette recorders just had a
fixed Dolby level in and out.
There are outboard Dolby units (I have one made by Advent), which
make it possible to play back a Dolby B-encoded tape and adjust the
levels until it sounds right. (We did this with the soundboard
cassette of the Elvis Costello performance of "Ship of Fools" and "It
Must Have Been the Roses" for _Stolen Roses_).
--
David Gans [EMAIL PROTECTED]
Truth and Fun, Inc., 484 Lake Park Ave #102, Oakland CA 94610-2730
New CD: "Solo Acoustic" - info at http://www.trufun.com/perfectible
