Re: QDMC progress, updated

Guess I updated to soon, I finally have some information about what 
technique is used inside QDMC. This image is a psd taken from a 
wav->mu-law->wav file:

http://tranquillity.campus.luth.se/~banan/qdmc/PICS/ulawpsd.jpg

And if you compare the psd with the one in the pdf the similarity is 
striking.
I'm not sure of the reduction this gives, I think its 2:1 (16->8 bits). 
My current
guess for a decoder is this:

calculate checksum -> ????? -> ifft -> mu-law -> wav

This page/book has good information about mu-law and other sound stuff:

http://www.dspguide.com/ch22.htm


If one take a minute and remember the computing power that was availible 
in 96-97, theise
kind of techniques makes good sense. And the knowledge of compression 
wasn't as great as it is now.
That and the fact that LBpack (QDMC?) was most likely created by one 
person indicates that the whole
format is not so complicated. (I hope)

MvH
Benjamin Larsson



Benjamin Larsson wrote:

> Still no info about the technique used in the codec but I succeded in 
> locating a simple checksum routine used in QDMC2. The info is in the 
> updated pdf file. Note that most of the info in the document is mostly 
> guesses, except the facts section.
>
> http://tranquillity.campus.luth.se/~banan/qdmc/qdmc2.pdf
>
>
>
> MvH
> Benjamin Larsson





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