Hi,
Dolby A (etc.) decode. Would it not be possible to to do this with
convolution ?? Find a working unit, record its impulse response, use
that in one of the many convolution reverb/filter plug-ins. While
doing that record the encode impulse response for those who want to
use it as an effect (e.g. on backing vocals).
Obviously the Dolby reference level would have to be taken into account.
Apologies if this is a completely hare-brained idea.
Dave Hunt
Date: Mon, 29 Apr 2013 21:56:30 -0500
From: David Pickett <d...@fugato.com>
Subject: Re: [Sursound] Sony PCM? (was Re: DTS Headphone:X)
A standalone Windows app that would decode Dolby-A encoded wavefiles
and output a restored non-Dolby 24-bit wavefile would be most
useful. I have several recordings that I have had transfer to hi-res
files still in Dolby-A format.
... even if such a program were command line only and needed to be
left overnight to cook!
David
Date: Tue, 30 Apr 2013 10:18:37 +0100
From: Dave Malham <dave.mal...@york.ac.uk>
Subject: Re: [Sursound] Sony PCM? (was Re: DTS Headphone:X)
<snip>
One possibility would be to use Spice to model the circuit and just
process
the sound files through the model. Slower than a directly written
program,
but probably usable for archival work.
Dave
------------------------------
Date: Tue, 30 Apr 2013 10:39:27 +0100
From: Dave Malham <dave.mal...@york.ac.uk>
Subject: [Sursound] Dolby A (was Re: Sony PCM? (was Re: DTS
Headphone:X))
Dolby A used sided chained compression of signals on record (and
corresponding expansion on replay) so only low level signals where
affected
- over the Dolby Level there was essentially no affect on the
signals and
they passed straight through. A good deal of psychoacoustic work
was done
to ensure that artefacts such as noise pumping were well hidden,
including
splitting up the signal into several frequency bands so that
signals in one
band didn't affect others and time constants could be optimised.
Telecom C4
also split into bands (for the same reasons) but didn't sidechain so
compression was applied at all signal levels. This meant you got more
noise reduction but also more artefacts, though not as much as DBX
which
used neither sidechain nor bands. Dolby A, because of its
sidechains had to
be aligned to within half a dB of the correct level or the process
went
wrong because the compression thresholds went out but neither C4
nor DBX
needed anything other than aligning to optimise machine dynamic
range as
they had no thresholds. This would seem to make Dolby A more
difficult to
use but as every Dolby A unit incorporated a proper Dolby Tone
generator
which produced a unique warbling test tone that all Dolby A tapes
should
have on them, this shouldn't be a problem.
Dave
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