Archiving this. It's gold. On Mon, 2010-08-30 at 12:00 +0100, Ralph Corderoy wrote: > Hi, > > There's another installment from Dave Beazley on his Superboard II. > This time he's decoding an audio recording from it into bytes. (Some of > the Python may be a bit harder to follow than before.) > > Decoding Superboard II Cassette Audio Using Python 3, Two > Generators, and a Deque > > http://dabeaz.blogspot.com/2010/08/decoding-superboard-ii-cassette-audio.html > > He uses a deque as a sliding window over the audio samples, maintaining > a count of the number of zero-crossings in the deque. Given that the > `silence' before the data starts is the high frequency of a 1 and the > start-bit is a lower-frequency 0, when that ZC count drops low enough, > he knows the start bit sits squarely in the deque. He can then chomp > through the following audio samples a bit's worth at a time until the > whole byte and two stop-bits are consumed before returning to the > sliding window search. > > http://en.wikipedia.org/wiki/Deque > http://en.wikipedia.org/wiki/Zero-crossing > > He provides code and WAV to download and run. Here's the output with > cat(1) showing up the CR, NUL, ..., LF that the SII outputs as a delay > for when it has to read and process the data later. > > $ python3 kcs_decode.py osi_sample.wav | cat -A > ^...@^@^...@^@^...@^@^...@^@^...@^@$ > ^...@^@^...@^@^...@^@^...@^@^...@^@$ > 10 FOR I = 1 TO 1000...@^@^...@^@^...@^@^...@^@^...@^@$ > 20 PRINT I;^...@^@^...@^@^...@^@^...@^@^...@^@$ > 30 NEXT i...@^@^...@^@^...@^@^...@^@^...@^@$ > 40 end...@^@^...@^@^...@^@^...@^@^...@^@$ > ok...@^@^...@^@^...@^@^...@^@^...@^@$ > $ > > I expect the next installment will be to translate a subset of Python > bytecode to 6502. :-) > > Cheers, > Ralph. > > > -- > Next meeting: Blandford Forum, Tuesday 2010-09-07 20:00 > Meets, Mailing list, IRC, LinkedIn, ... http://dorset.lug.org.uk/ > How to Report Bugs Effectively: http://bit.ly/4sACa
-- Next meeting: Blandford Forum, Tuesday 2010-09-07 20:00 Meets, Mailing list, IRC, LinkedIn, ... http://dorset.lug.org.uk/ How to Report Bugs Effectively: http://bit.ly/4sACa
