Looking for basics of reading audio frequencies in C [closed]

Question

I don't want to use libraries- I want to write from scratch. I want to play around making a decoder for WEFAX transmitted over the radio. Different audio frequencies convert to different pixel darknesses. Gray scales only - no color.

There are 120 lines per minute each with somewhere over 1000 pixels. I want to detect the frequency and turn it into probably an 8 bit value. The hardware equivalent would be something like an LM567 frequency to voltage converter.

I haven't any idea where to start. Is this something like an FIR or IIR? Can anyone point me to code I can study? I'm not writing for Windows, strictly unix.

Alan

Answer 1

you could do it just with a timer and zero crossing to find out the fundamental frequency

http://en.wikipedia.org/wiki/Zero_crossing