Subj : Re: Audio Encoding
To   : comp.programming
From : Giannis Papadopoulos
Date : Sun Aug 21 2005 06:50 pm

brendan wrote:
> Does anyone have any ideas on how to write code to turn binary 
> (pictures, video, etc.) into a sound track (a bit like DAT) that can be 
> compressed with A-Track losslessly? Or am I being completely stupid? If 
> you could encode the track into a (very large) file that had no pitch 
> differences:
> 
>  bits:1 0 1 0 1 0 1
> audio:/\/\/\/\/\/\/\
> 
> Wich is then compressed. As the waveform would be so simple the A-Track 
> could (?) compress it as lossless.

You'll have to modulate your bit-stream.

First, make your data a single data stream and then choose some kind of 
modulation (BPSK, QPSK, FSK or anything else). Then you can use an 
audible frequency as a carrier to modulate your data over it and write 
that frequency on your medium.

Then receive what you wrote on the medium, remove the noise and sample 
it or sample it and remove the noise and then demodulate.

You have to be very good at Signal and Systems and Digital Signal 
Processing. You could use a sound-card for all of these, but you surely 
have to create all the necessary code for frequency retrieval, phase and 
frequency offset correction, receiver and transmitter (the medium 
reader) timing synchronization.

Good luck.

-- 
one's freedom stops where others' begin

Giannis Papadopoulos
http://dop.users.uth.gr/
University of Thessaly
Computer & Communications Engineering dept.

.