Programming Sound with Pure Data (for james tumino) by Tony Hillerson

Author:Tony Hillerson
Language: eng
Format: epub
Tags: Pragmatic Bookshelf
ISBN: 978-1-93778-566-6
Publisher: The Pragmatic Bookshelf, LLC (480851)

Now before we generate more interesting waves, let’s address a few more things about this new patch. The first is why there is a 4 at the end of tabosc4~, and the second is why we used 1024 as the first argument to sinesum.

The tabosc4~ object has a 4 at the end of it to signify that it uses 4-point polynomial interpolation as it converts a constant number of data points from an array into a signal at different frequencies. Basically this means that it will do its best to smooth out the signal as it jumps from point to point of data in the array, no matter at which frequency the oscillator is generating a signal.

This is directly related to why we passed 1024 to the sinesum function. The help for tabosc4~ says that it expects the size of the array that it plays to be a power of two with an additional three points, one at the beginning and two at the end. The additional point at the beginning should be the same value as the final point in the array, excluding the two additional end points, and the final two should be copies of the first point in the array, excluding the additional beginning point. This is so that the tabosc4~ can make a smooth transition between each period of the wave. Luckily using sinesum or cosinesum takes care of this for us, as well as resizing the array.

When we specified 1024 as the size of array to generate, sinesum actually generated the extra transition points and added them to the array, resizing it to 1027. We used 1024 because it gives us plenty of room for enough points to make a nice-sounding sine wave. The help entry for tabosc4~ suggests using an array of size 512 for any generated wave with up to 15 partials. When generating above 15 partials it suggests using 32 times the number of partials and then rounding that up to a power of 2. Since we generated only one partial, 1024 is twice as big as the Pd manual says it needs to be. This could be a tradeoff between superhigh quality and memory.

Now let’s look at generating some different waves with many more than just one partial.

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