The musical pieces listed above have been created by computer.
The principle that I've used is extremely simple:
A program that I've called 'Soundmaps' repetitively sends
data contained in bitmaps to the PC's soundcard. The bitmaps can
be static (e.g. a photo) or dynamic (a rectangle on the desktop).
In the latter case, the image contained inside the rectangle will
change when manipulations are carried out in a drawing program. Hence, the sound changes while drawing, typing
or surfing, thus allowing for interactivity.
The bitmap pixels can be sent to the soundcard without any data
manipulation, which results in a rather high-pitched noisy
sound (as in 'Pond'). In a second mode, each scan line
of the bitmap is interpreted as a frequency spectrum, bass on
the left, soprano on the right. Fourier transformation (i.e.
transformation from the frequency- to the time-domain) of each
scanline, before sending the data to the soundcard, results in
a sound that may give the impression of rising bubbles or tinkling
bells. In the third mode, each scan line is interpreted as a keyboard,
each pixel on the scan line being a white or black key. As with
MIDI, the keyboard may be associated with an instrument.
In that case the bitmap fulfils more or less the same role as
piano rolls in former times.
Bitmap data is sent to the soundcard in an indefinite loop. The
duration of the loop determines the rhythm of the sound, at least
if the loop is not too long (<3 sec). Usually, multiple rectangles
and bitmaps are active simultaneously (as in the figure on top
of this page that has five of equal dimensions). Simultaneously playing bitmaps of not quite equal
sizes gives interesting effects (as in 'Curved air') perhaps reminiscent
of pieces by Steve Reich, who employed the idea of phase changes
several times in his works.
Some pieces like 'Papillon' use neither metrum nor a particular
musical scale. Others, like 'Ode to Terry Riley' use a
major heptatonic scale, try to prevent dissonants and respect
metrum. Harmonic rules limit the number of notes that can
be played, giving some impression of melody.
'Fractale binaire' has been created by playing a movie
on the computer screen over which about six 'sound windows' were
laid. As the movie in question was showing a portion of the Mandelbrot
set that was slowly zoomed into, 'fractale binaire' only slowly
evolves in consequence.
'Sounds from a square' and
'Eight chicks in concert'
have also been created by videos. The videos show only movement.
The background becomes invisible.
A breeze sets the tree leaves in motion every now and then.
Two persons can be seen when they walk about the square but disappear when they stand still.
'Ja-nee' has been created initially for Annie Abrahams.
A user friendly version of soundmaps is available for download.