I'll try to go into a bit deeper explanation here.
Let's take an example, we'll start with the simple:
This small example would just create a simple line, no more, no less, no response, no nothing.
x=0; would on the other hand create nothing but a small 1pixel dot at the middle of the horizontal scale in the AVS window.
x=i; what is this then?
i is a small function that creates a line, on every pixel it has a value on the X scale, starting at 0, going up to 1.
It only ranges from 0 - 1 in the normal state without any extras.
x=i-0.5; here we add "-0.5" to the statement, this would cause the i variable to be subtracted by 0.5, thus instead ranging from -0.5 to 0.5 on the horizontal scale.
A normal example is:
x=i*2-1; here we duplicate i by 2, this changes the range to 0 - 2, but we go -1, and it ranges from -1 to 1 and covers the whole horizontal scale. Get the idea?
OK, let's move on.
x=i*2-1; (We create the line covering the x- scale)
y=v*.5; now what? we finally get to the "v" function, v gets input data from the sound, using waveform it ranges from -1 to 1, we'll stick to that.
the sound makes this move up and down, every point reacting to that specific point on the "sound scale".
We use v*.5 because the normal wave is often to big.
Now you've got a simple line covering the x-scale and reacting to sound.
W and H are often not that useful, they are always equal to the width and height of your AVS window, and may be used if you want more specific details in "N".(the number of points on your screen.)
This should answer your question