How Sinclair computer interprets audio and loads code
Hello,
First time posting here, so sorry if the question is already answered or is unanswerable.
I am trying to find some info about how sinclair computers interpret audio for loading the games.
Could some one direct me to a certain source or an existing forum thread please.
I am hoping to implement a similar process in Java or Max/Msp for a much simpler purpose, namely load an jpg image using audio input and the other way around. I have done some tests with detecting frequencies of a sinewave, where a certain frequency value (in time) represents a location of a pixel, that worked but it was extremely slow and inefficient.
As far as i know in sinclair computers that happens on a much lower level where (if i am correct) positive or negative parts of a square wave represent 0s and 1's. Listening to a few old game cassettes I have, I can also hear that there are also sine waves, and the frequency content of the rest of the sounds is very varied. I wonder how that analysis is performed (so fast), is there a common technique for such a thing that I could read about?
There's probably much more to that, so first maybe somebody could direct me to the right direction.
thanks a lot.
First time posting here, so sorry if the question is already answered or is unanswerable.
I am trying to find some info about how sinclair computers interpret audio for loading the games.
Could some one direct me to a certain source or an existing forum thread please.
I am hoping to implement a similar process in Java or Max/Msp for a much simpler purpose, namely load an jpg image using audio input and the other way around. I have done some tests with detecting frequencies of a sinewave, where a certain frequency value (in time) represents a location of a pixel, that worked but it was extremely slow and inefficient.
As far as i know in sinclair computers that happens on a much lower level where (if i am correct) positive or negative parts of a square wave represent 0s and 1's. Listening to a few old game cassettes I have, I can also hear that there are also sine waves, and the frequency content of the rest of the sounds is very varied. I wonder how that analysis is performed (so fast), is there a common technique for such a thing that I could read about?
There's probably much more to that, so first maybe somebody could direct me to the right direction.
thanks a lot.
Post edited by Auris on
Comments
Square wave. Each "tone" consists of two edges - hi and low signal. Number of tones determine bit status - long (many tones) == 1, short (fewer tones) == 0.
D.
http://www.worldofspectrum.org/ldbytes.html
has a little on it.
A '0' bit takes two 855 T halfpulses
A '1' bit takes two 1,710 T halfpulses (twice the length of a '0' bit)
This works out to two tones with fundamental freq 1kHz and 2kHz. Typical analogue audio cassettes have a passband from 50 Hz to 12.5kHz.
Write games in C using Z88DK and SP1