Re: [microsound] wave terrain synthesis

[<tom@xxxxxxxxxxxxxxxxx>]

Hi...

Imagine what a standard wave form looks like, ie.e a line from left to right
that wobbles somehow and consists of one repeating form
(Such as a Sine wave or square wave e.t.c.) In many synthesis applications
this data is stored in a wavetable, an array of values, usually floating
point numbers
ranging from -1 to +1. This table is then read through at the the frequency
of sound you require...
For example..
if the table is 44100 numbers long and you read it at 44100 number per
second, you have created a 1HZ audio wave.
When you reach the end of the table you start again by wrapping around to
the start.
Reading the table faster (say at 440hz) means skipping values in the array
so you can cylce the table faster and produce a higher frequency wave.

OK. so a wavetable is 1d.. a list of numbers and the reader (sometimes
called the phase point) cycles through it and spits out the values to your
card.
A waveplane is 2d like a greyscale bitmap it consists of a 2d grid of
values. The reader this time moves in a shape around the plane, say a
circle.. the speed at which it completes this circular motion dictates the
frequency of the wave heard. if it tkaes 1 sec to do a whole loop and you
are at samplerate 44100, it plays back 44100 values and makes a 1HZ wave.
Same as wavetable synthesis the reader can speed up and skip points,wrapping
around to its start to make higher freq waves. Imagine drawing the values
that the reader passes over into a normal 1d wavetabel/waveform and you will
get the idea.

The advantages of waveplanes are that the reader path can be manipulated by
more that just frequency, the centre of the circle can be shifted over time
or the shape changed entirely (however you should maintain the same number
of readpoints on a changing shape to maintain the same freq/pitch). This
allows for the wave itself to morph from one shape to another. The terrain
itslef could be altered also..

There are few programs that support this sort of synthesis, and use
different techniques (the link you posted shows a method using a math
function to define the plane, this is good for low memory usage and fp
accuracy, however you could easily use a bitmap based method also)

You may need to hunt about a bit for a working example, and even programming
one in PD may take a while.
Let me know if you find one..

Hope this helps

Tom Betts
http://www.nullpointer.co.uk

----- Original Message -----
From: "Tim Mortimer" <tmortimer@xxxxxxxxx>
To: "microsound" <microsound@xxxxxxxxxxxxx>
Sent: Thursday, December 05, 2002 6:04 AM
Subject: [microsound] wave terrain synthesis

> ok.
>
> ive seen this.
>
> http://www.cim.mcgill.ca/~clark/nordmodularbook/nm_oscillator.html#terrain
>
> can anyone offer any additional links or info about wave terrain
synthesis?
>
> i get the basic concept, but am uncertain in the above example how the
> tracing of the circular motion on the terrain occurs.. a nice simple hand
> holding analogy anyone?
>
> .& what kind of adjustments or additions could be made to the example
> formula...
>
> (& please consider the desired terms of address to be "laymans".... my
> maths/ programming knowledge is very limited - toying around in reaktor is
> about as far as i get - im on pc... a bit scared off by Csound or PD at
the
> moment, despited being interested & somewhat drawn to the concepts,
> obviously, as im on this list  ; )
>
> anyway, i digress. many thanks.
>
>
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