<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body>
<p>Hi, Tim,</p>
<p>Ah, another difficult-to-deal-with format. Someone gave me a
wooden carving of a person sitting in the lotus position with his
head in his hands...and I was told that was me when another format
was announced. <br>
</p>
<p>I kind-of knew what AC-2 and AC-3 are/were, but did a little bit
of research. By way of introduction (from
<a class="moz-txt-link-freetext" href="https://www.sweetwater.com/insync/ac-2/">https://www.sweetwater.com/insync/ac-2/</a> ),</p>
<p>
<blockquote type="cite">Another of <a
href="https://www.sweetwater.com/insync/dolby-2/">Dolby Labs’</a>
sound encoding schemes. Dolby AC-2 is a perceptually based
adaptive transform coding algorithm that combines very high
audio quality with a low bit rate, thus substantially reducing
the data capacity required in such applications as satellite and
terrestrial links and digital audio storage media. The digital
algorithm developed by Dolby uses a multi-band approach to take
advantage of psychoacoustic masking. A bit allocation scheme
based on 80% fixed allocation and 20% adaptive allocation keeps
the complexity of the codec relatively low. Dolby both
manufactures professional codecs incorporating AC-2 (such as
Dolby FAX) and licenses the technology to other manufacturers
for inclusion in their products.</blockquote>
Googling Dolby FAX led me to the manual for the DP503 which I
found here<br>
<a class="moz-txt-link-freetext" href="https://www.manualslib.com/manual/40630/Dolby-Laboratories-Dp503.html?page=17">https://www.manualslib.com/manual/40630/Dolby-Laboratories-Dp503.html?page=17</a><br>
(the entire manual is available for download)<br>
I have it here:<br>
<a class="moz-txt-link-freetext" href="https://www.dropbox.com/s/rn73knm5syogsfh/dp503.pdf?dl=0">https://www.dropbox.com/s/rn73knm5syogsfh/dp503.pdf?dl=0</a><br>
and I already had the datasheet here:<br>
<a class="moz-txt-link-freetext" href="https://www.dropbox.com/s/3pwnfxmr4m52g3l/503brochure.pdf?dl=0">https://www.dropbox.com/s/3pwnfxmr4m52g3l/503brochure.pdf?dl=0</a></p>
<p>Alas, the DP503 is the encoder, but there is a lot of information
in this. The data sheet says the Dolby DP524 is the corresponding
decoder.<br>
I have the datasheet here:<br>
<a class="moz-txt-link-freetext" href="https://www.dropbox.com/s/76oxnm0e3xke725/524brochure.pdf?dl=0">https://www.dropbox.com/s/76oxnm0e3xke725/524brochure.pdf?dl=0</a><br>
Note that the Dolby products only work at 48 ks/s in AC-2. I don't
know if the ISDN applications used different sampling frequencies.
(below might help).<br>
Manualslib.com also had the 524 manual<br>
<a class="moz-txt-link-freetext" href="https://www.dropbox.com/s/jtvkufkkyliw4et/dp524.pdf?dl=0">https://www.dropbox.com/s/jtvkufkkyliw4et/dp524.pdf?dl=0</a><br>
<br>
This site appears to have one in stock:<br>
<a class="moz-txt-link-freetext" href="https://www.broadcaststore.com/store/model_detail.cfm?id=797496">https://www.broadcaststore.com/store/model_detail.cfm?id=797496</a><br>
and there is one on eBay for $25<br>
<a class="moz-txt-link-freetext" href="https://www.ebay.com/p/2263853666">https://www.ebay.com/p/2263853666</a></p>
<p>I think this was one of many systems used mostly for ISDN. I
wonder if there are software decoders available--if so, they might
only run on old systems, but this is going back 25 or more years
as I understand it.</p>
<p>There is an interesting article on ISDN systems from 1997. This
URL is the first page of the article, but you can munge the URL to
see additional pages.<br>
<a class="moz-txt-link-freetext" href="https://worldradiohistory.com/hd2/IDX-Audio/Archive-Studio-Sound-IDX/IDX/90s/Studio-Sound-1997-03-OCR-Page-0093.pdf">https://worldradiohistory.com/hd2/IDX-Audio/Archive-Studio-Sound-IDX/IDX/90s/Studio-Sound-1997-03-OCR-Page-0093.pdf</a></p>
<p>AC-2 was rapidly replaced with "Dolby Digital" originally known
as AC-3.</p>
<p>I was never deeply involved with these systems other than at a
high level. <br>
</p>
<p>What was the library system that used it? <br>
</p>
<p>Cheers,</p>
<p>Richard</p>
<p><br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 2021-12-09 1:04 p.m., Tim Požar via
ProAudio wrote:<br>
</div>
<blockquote type="cite"
cite="mid:892b0cac-d65e-e855-f7fd-886b93677b68@lns.com">Gang... I
am trying to help a station migrate an automation system library.
Alas, it is encoded in Dolby AC-2. I can't find a way to convert
AC-2 into something more standard. Any pointers to programs /
libraries / plug-ins that can support decoding Dolby AC-2 into PCM
or something else? Ideally something that I can script up to
process 6,000 or so cuts.
<br>
<br>
Thanks in advance.
<br>
Tim
<br>
_______________________________________________
<br>
ProAudio mailing list
<br>
<a class="moz-txt-link-abbreviated" href="mailto:ProAudio@bach.pgm.com">ProAudio@bach.pgm.com</a>
<br>
<a class="moz-txt-link-freetext" href="http://bach.pgm.com/mailman/listinfo/proaudio">http://bach.pgm.com/mailman/listinfo/proaudio</a>
<br>
</blockquote>
<pre class="moz-signature" cols="72">--
Richard L. Hess email: <a class="moz-txt-link-abbreviated" href="mailto:richard@richardhess.com">richard@richardhess.com</a>
Aurora, Ontario, Canada <a class="moz-txt-link-freetext" href="http://www.richardhess.com/">http://www.richardhess.com/</a>
<a class="moz-txt-link-freetext" href="http://www.richardhess.com/tape/contact.htm">http://www.richardhess.com/tape/contact.htm</a>
Quality tape transfers -- even from hard-to-play tapes.</pre>
</body>
</html>