Best handling of beeps

Daniel Vik
daniel@vik.cc
http://danielvik.com/

Judges' comments:

To build:

make

To run:

./prog > foo.c

Try:

echo 'Want to hear me beep?' | ./prog  > audio_file.raw

echo 'No. I want chocolate!' | ./prog | mplayer -demuxer rawaudio -

Selected Judges Remarks:

This program sets a new tone for obfuscation. But do you understand what it says about obfuscation? Perhaps:

./prog < prog.c > prog.raw

might speak to your coding style? If not, then perhaps:

./prog < remarks.markdown | mplayer -demuxer rawaudio -

might help? :-)

Author’s comments:

Remarks

This program converts ascii text to morse audio file and vice versa. As far as I can tell, there are at least six chocolate references in this program.

This program can convert text to morse to a raw 44.1kHz stereo audio file. Via streaming to mplayer, you can listen to the morse audio.

Don’t forget the last ‘-’ as it makes mplayer read from stdin.)

Convert audio file with morse signals to text

$ ./prog e < audio_file.raw

or alternatively pass a .wav file as input.

The preferred input format 44.1kHz stereo, but it does a decent job on mono input and different frequencies as well.

Portability

The program is portable to most platforms. The only system dependency is that the program relies on writing binary data to stdout.

Microsoft compilers adds a carriage return to newlines, and to compile the program with this platform, the following line can be added after the main declaration in order for the program to run correctly:

_setmode(_fileno(stdout), 0x8000);

Known Issues

The program uses a quite simple algorithm for detecting tone on and off events in the morse signal. Hence the program does not work well with noisy input signals. I have tested it with several samples of man made morse recordings as well as computer generated ones.

Generally, any recording from ham radio transmissions does not decode due to noise and echoes. Other man made recordings may decode, but some characters can be incorrect due to too big variation in length of tones and pauses. However I found some man made recordings on that decode reasonable well.

If a recording don’t decode, you could try to pre-process the input with a narrow bandpass filter on the frequency of the transmission.