The Vorbis audio format, uses something called the Modified
Discrete Cosine Transform (MDCT). I was interested in how this
worked, but did not know where to start. Is this the name of a
particular algorithm, or does it just mean something like a
cosine transform, but not quite right? So I asked the Vorbis
mailing list. Nobody answered.
It was not a high priority, so I did other things for about a year.
I got interested again, so I did a Google search for MDCT.
I got just a few hits, one of which was my own mailing list question
from a year previous.
I can almost hear you saying that you are tired of people whining
about lack of documentatation, but this is not a complaint, it is
an announcement that I did something about it. I searched the
local library and the internet, came up with a few definitions,
removed the errors and differing sign conventions and worked out
the details.
This doesn't count as research; it is, of course ``well known'' in
the mathematician's sense. Nevertheless, my experience leads me
to believe that it is not perfectly trivial to actually become one
of those who know.
Abstract
--------
Assuming only basic trigonometry, we define the Modifed
Discrete Cosine Transform (MDCT), and prove its basic properties.
The dread words ``it can be shown'' do not occur.
This document is not complete, but I am releasing the draft
because there is enough here that it may be useful to someone.
Comments and suggestions for improvement are welcome, especially
if you know the answers to any of the questions at the end.
It can be found at http://www.free-comp-shop.com/vorbis.html
--
-- Keith Wright <kwright@free-comp-shop.com>
Programmer in Chief, Free Computer Shop <http://www.free-comp-shop.com>
--- Food, Shelter, Source code. ---
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That's a rather impressive and well written document you have there. Ought to be on the Vorbis site actually, if I had a say. Given some time with it, even I will be able to understand what MDCT is after all. Splendid work! Linus <p>--- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.
> It can be found at http://www.free-comp-shop.com/vorbis.htmlThanks for your efforts. May I suggest compressing the Postscript file, possibly with zip or gzip, to save bandwidth? <p> -- "Knowledge is knowing a street is one way. Wisdom is still looking in both directions." dubious9 on Slashdot Nicola Larosa - nico@tekNico.net --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.
Would it possible for you to make a PDF file of this document as well, for all us windows users? /Erik Keith Wright wrote:>It can be found at http://www.free-comp-shop.com/vorbis.html > >--- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.
I dump it into the distiller for you - click below to pick it up.
http://www.babinszki.com/distiller/out/vorbis.pdf
-Myle-
--
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"If the world didn't suck, We'd all fall off"
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<p>-----Original Message-----
From: Erik Stenborg [mailto:d99papa@dtek.chalmers.se]
Sent: Friday, May 23, 2003 05:21
To: vorbis@xiph.org
Subject: Re: [vorbis] Description of MDCT
<p>Would it possible for you to make a PDF file of this document as well,
for all us windows users?
/Erik
Keith Wright wrote:
>It can be found at http://www.free-comp-shop.com/vorbis.html
>
>
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This is a really excellent description, Keith. I was surprised I remembered enough of complex analysis to skip the first section, but the rest of it made perfect sense. My hat's off to you. Cheers, Kyle Keith Wright <kwright@gis.net> writes:> I can almost hear you saying that you are tired of people whining > about lack of documentatation, but this is not a complaint, it is an > announcement that I did something about it. I searched the local > library and the internet, came up with a few definitions, removed > the errors and differing sign conventions and worked out the > details.--- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.