Wavetable synthesis in PD

Reply to Wavetable synthesis in PD on Sun, 30 Mar 2014 19:48:50 GMT

Pd_patchmaker — Sun, 30 Mar 2014 19:48:50 GMT

Hey, I'm working through Andy Farnell's Designing sounds...in the chapter on wavetable synthesis, he uses the word "index" a lot...I tried flipping back to earlier chapters, but never really found an explanation...

"...the index is placed centrally around the middle of a table," "we keep the indexing waveform fixed," "the table is filled...and we index it with a phasor" etc.

what does "index" mean in this context?

Reply to Wavetable synthesis in PD on Mon, 31 Mar 2014 09:22:34 GMT

James — Mon, 31 Mar 2014 09:22:34 GMT

A table or array is filled with a number of values, each of which can be addressed by it's 'index'. Look at the help file for [tabwrite]

Reply to Wavetable synthesis in PD on Tue, 01 Apr 2014 16:32:32 GMT

Pd_patchmaker — Tue, 01 Apr 2014 16:32:32 GMT

I did read the help file (before I posted) and still don't get it. And what do you mean by "addressing the index"?

Reply to Wavetable synthesis in PD on Tue, 01 Apr 2014 16:51:18 GMT

seb-harmonik.ar — Tue, 01 Apr 2014 16:51:18 GMT

Index has a few meanings, actually. On the programming side, an index is usually a lookup into an array, so say if you have an array of 4000 things, you can for instance look at the 3000th and say that you are reading it at the index 3000. In another sense, Index is what you multiply a modulating waveform by in order to get a greater degree of modulation. Also in FM synthesis the index is sometimes defined as the deviation (amount the modulator changes in both directions) divided by the frequency of the modulator

Reply to Wavetable synthesis in PD on Wed, 02 Apr 2014 17:28:29 GMT

mod — Wed, 02 Apr 2014 17:28:29 GMT

here's a simple example:

say i have a single ramp from 0 to 1 over 1000ms stored in a table at 44100 hz. The table will be 44100 samples long.

if i choose sample #0, then the value will be 0

if i choose sample #22050, the value will be (very close to) 0.5

if i choose sample #44099, the value will be 1

all of those sample #numbers, are the 'index'. And PD can read them in a variety of ways.

for example, with [tabread], you can get a simple float output:

[4410(
|
[tabread mytable]

because the table is 44100 samples long, then 4410 will be equal to (or very close to) 0.1

similarly, we can use [tabread~] with signals to drive the index, rather than floats.

so, for example, the following construct will oscillate our table from index 0 to 44100 and back again in a sinewave form. (We first scale the sinewave to 0 to 1 range, because normally [osc~] goes from -1 to 1)

[osc~]
|
[+~ 1]
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[*~ 0.5]
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[*~ 44100]
|
[tabread~]
|

Reply to Wavetable synthesis in PD on Wed, 02 Apr 2014 19:32:32 GMT

domien — Wed, 02 Apr 2014 19:32:32 GMT

Crystal clear as ever mod. You don't happen to be a teacher, do you?

Reply to Wavetable synthesis in PD on Thu, 03 Apr 2014 16:32:43 GMT

mod — Thu, 03 Apr 2014 16:32:43 GMT