RTTY encoding and decoding in Max


Today I was able to get an AFSK (audio frequency shift keying) system running in Max – sort of – It encodes text into ASCII bits and decodes the signal back into text – with a clock set at around 30ms (32 bits/second) – but there is no clock synchronization yet. Or stop bits, etc., The patch just uses the transmitter clock to sync the receiver (cheating)

Listen to an example of the word ‘hello’ at 32 bits/sec

local file is in max teaching examples/rtty-sim5.maxpat

Next step will be to get receiver sync happening – then make it conform to RTTY standard – probably a few days effort for this, but at least this is a proof of concept.

The synchronization may need to happen at the sample level (gen~) because it requires finding the beginning and end of bits – in order to set the clock pulses accurately.