TrikTraks starts being fun when you abandon linear changes over time and start in with non-linear ones.
Linear changes are a default in this program. They are ``stipulated'' by not calling for something else. But they are nothing special. All that is required is some path for the changes to follow. The shape of the path will affect the sound.
Take the same data file as above, without the amplitude changes, and add the following to it:
output(sound.wav) # name of the output soundfile
duration(5) # duration of the transformation
initial(1) # play the initial state for these many seconds
final(1) # play the final state for these many seconds
20 40 # element 0: duration in samples
1000 # amplitude
30 60 sin # element 1: duration in samples
-10000 # amplitude
40 80 # element 2: duration in samples
10000 # amplitude
10 20 sin # element 3: duration in samples
-500 # amplitude
Save the file, run TrikTraks on it, and listen to the output. You should again hear an initial 440-hertz tone, a final 220-hertz tone, but a varying glissando in the middle.
So what's going on?
Element 0 has an initial duration of 20 samples, and a final duration of 40 samples. This means that over 5 seconds, the value 20 slowly increases until it gets to 40 (20, 21, 22, 23, etc.). This increment happens evenly over the course of 5 seconds.
Element 1 has an initial duration of 30 samples, and a final duration of 60 samples, but follows the path of a sine wave to get from the initial to the final value.
Similarly with elements 2 and 3: 2 follows a linear path from 40 to 80, and 3 follows the path of a sine wave from 10 to 20.
Here's a plot of what the transformations look like for all four elements. (Note: this is a plot of the transformations, and not of the sound itself.) The elements are listed bottom to top, with the first element on the bottom.
The horizontal axis represents iterations (or time), and the vertical axis represents the normalized magnitude of the variable. (``Normalized magnitude'' just means that the values have been scaled to fit together on one plot.)
In this plot, the first element (at the bottom) has a choppy diagonal line, and a horizontal line in the center. The choppy, diagonal line represents the duration, ascending from 20 to 40 samples. The horizontal line represents the amplitude, which does not change.
The second element (second from bottom) has a sine wave and a horizontal line. The sine wave represents the duration, oscillating between 30 and 60 samples, and the horizontal line represents the amplitude, which is fixed at -10000. (The other two elements should be interpreted in a similar way.)
So, in this plot you can see that the durations of elements 1 and 3 follow the path of a sine wave, whereas the durations for elements 0 and 2 follow a linear path.
So, elements 0 and 2 are getting steadily longer, but elements 1 and 3 first get longer, then shorter, then longer again.
Since the frequency you hear is dependent on the sum of durations of all four elements at one moment, the frequency you hear keeps changing.
This changing ``path'' of durations (and of amplitudes too) is where the name comes from: TrikTraks.