Emulating a primitive modem / encoding data in audio

Hi all,

At the OFLab we started on a project to encode data into audio, basically creating the most primitive of modems, but then in open air. But we need it smarter, so I’m looking at this.


The 300 bit/s modems used audio frequency-shift keying to send data. In this system the stream of 1s and 0s in computer data is translated into sounds which can be easily sent on the phone lines. In the Bell 103 system the originating modem sends 0s by playing a 1,070 Hz tone, and 1s at 1,270 Hz, with the answering modem putting its 0s on 2,025 Hz and 1s on 2,225 Hz. These frequencies were chosen carefully, they are in the range that suffer minimum distortion on the phone system, and also are not harmonics of each other.

Which actually doesn’t really sound that complicated, but as I’m green concerning OF, I hoped some of the wise elder OF could give me a leg up ? What OF methods are there avaiable to modulate sound?

Kind regards,