RSA - the song

[Kent Crispin <kent@songbird.com>]

On Fri, Aug 01, 1997 at 11:35:02AM +0100, Adam Back wrote:
[...]
> 
> print pack"C*",split/\D+/,`echo "16iII*o\U@{$/=$z;[(pop,pop,unpack"H*",<>
> )]}\EsMsKsN0[lN*1lK[d2%Sa2/d0<X+d*lMLa^*lN%0]dsXx++lMlN/dsM0<J]dsJxp"|dc`
> 
> > I dug out a midi interpreter I wrote a number of years ago, 
> > and it is indeed trivial to modify it to read any text as input.  
> > Unfortunately, I wrote that long before the midi file spec was 
> > finalized, and the hardware I wrote it for is also long gone.  But 
> > it's probably not much work to get file output working again...and 
> > the thought of a general text-to-midi translator is rather 
> > entertaining -- I could play this entire mail message through it, for 
> > example... It would definitely make better music if some rhythmic 
> > variation was part of the coding, but that would make it a little 
> > harder to make an automatic decoder...
> 
> I'd find it most cool to hear an audio file of the above.

Well, I generated a midi file that encodes music which in turn is a 
direct algorithmic encoding of your program.  I didn't have a 
convenient way to go to a direct sound file, but midi players are 
very widely available -- any recent pc with a sound card will have a 
"multimedia midi jukebox" or something like that.  And there are 
probably free ones on the net -- I didn't look.  The midi file will 
be a mime attachment to this message.  It's also at 

	ftp://songbird.com/pub/rsa.mid 

For aesthetic reasons I modified the encoding from the simple one
mentioned earlier, and, rather than try to modify one of my earlier
midi programs, I just hacked this one out from other sources.  The
program will actually encode any binary data into a piece of music. 

I think that musically the piece is actually somewhat interesting -- I
kind of like it.  Like the source text, it is rather dense.  But if
you listen to it a few times patterns and phrasing will appear.  It 
sounds like reasonable avante garde music, actually -- something a 
college radio station might broadcast to the world late at night...

The program is really rather trivial, so rather than describing the 
encoding, I am just appending it to this message.

--------------------------------------------------------------------
/*
    dtom -- convert data to midi
        dtom midifile <datafile
            or
        datasource | dtom midifile

        convert standard in to a midi representation of the data, and
        write it to a standard midi file.  The midi data is designed
        to so that the sound produced will permit decoding by a pitch
        to midi device.  Two things are done to increase the musical
	interest:  First, the notes are selected from a diatonic 
	scale, instead of a chromatic.  And second, the rhythm is 
        also varied algorithmically -- any decoding from the sound 
        should ignore all rhythmic variation.

	Code uses "midifilelib" from Tim Thompson & Michael 
	Czeiszperger, and is cobbled from one of their examples.

*/
    

#include <stdio.h>
#include <ctype.h>
#include "midifile.h"

#define ROOT 36

FILE *fp;

/* offsets for three octaves of diatonic major scale */
int scale[] = {0,2,4,5,7,9,11,12,14,16,17,19,23,24,26,28,29,31,33,35,36};

mputc(c) { return(putc(c,fp));}

int writetrack(track)
int track;
{
    int note_duration;
    int rest_duration;
    int high_nybble;
    int low_nybble;
    char c;
    char n1[2];
    char n2[2];

    mf_write_tempo((long)100000);

    while( (c = getchar()) != EOF ) {

        high_nybble = (c>>4) & 0xf;
        low_nybble  = c & 0xf;
	
	/* low note */
        n1[0] = scale[low_nybble]+ROOT;	/* note number */
        n1[1] = 64;                     /* velocity */

	/* high note */
        n2[0] = scale[high_nybble]+ROOT+scale[16];
        n2[1] = 64;

	/* shouldn't happen */
	if( n1[0] >= n2[0] ) printf("warning -- voice crossover!\n");

	/* note_duration needs to be long enough for pitch detectors */
	note_duration = 120*((c&15) + 4);
	rest_duration = 120*(((c>>5)&3));

        if(!mf_write_midi_event(rest_duration,note_on,1,n1,2)) 	return(-1);
        if(!mf_write_midi_event(0,note_on,1,n2,2))		return(-1);

        if(!mf_write_midi_event(note_duration,note_off,1,n1,2))	return(-1);
        if(!mf_write_midi_event(0,note_off,1,n2,2))		return(-1);
    }

    return(1);
} /* end of write_track() */

main(argc,argv)
char **argv;
{
    if( !(fp = fopen(argv[1],"w")) ) exit(1);

    Mf_putc = mputc;
    Mf_writetrack = writetrack;
    mfwrite(0,1,480,fp);
}

---------------------------------------------------------------------------


-- 
Kent Crispin				"No reason to get excited",
kent@songbird.com			the thief he kindly spoke...
PGP fingerprint:   B1 8B 72 ED 55 21 5E 44  61 F4 58 0F 72 10 65 55
http://songbird.com/kent/pgp_key.html

rsa.mid