Messages in this thread |  | | | From | "Albert D. Cahalan" <> | | Subject | Re: Speaker twiddling [was: Re: Panicking in morse code] | | Date | Mon, 29 Jul 2002 16:35:42 -0400 (EDT) |
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Pavel Machek writes:
> You might even add FSK checksum at each end of morse line ;-), if you realy > want checksum. Plus it will sound cool. You should also play special melody > at each start of repeat, to be more decoder-friendly [and it will also > sound cool].
I looked into writing a decoder. It's really helpful to have a fixed ratio of high/low states. It's also good to avoid silence. The melody is important, so the user will know how long to record, and to provide a way to sync up the decoder.
AMTOR w/ FEC is looking pretty good, but it needs the character set fixed. (new shift states, 1 ASCII per 2 Baudot, or a new code table) I hear there are extensions available that would at least do lowercase and a bit more puctuation.
Not being a DSP expert, I'm using an FFT to get the power spectrum for a small region. I slide this window along the audio sample. I have pretty pictures of the bits now. :-) It looks like I could pick a frequency with a wide range of thresholds that give me the proper mark:space ratio, then recover the clocking... It's not too hard I think, even after going *.wav --> *.ogg --> *.au or misinterpreting the data type.
So this is 100 baud. Guessing at good frequencies: 1940 HZ and 1500 HZ 1600 HZ and 1140 HZ (wide separation needed because I'm not a DSP expert) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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