On 04 Aug 2016, at 18:01, Claude Heiland-Allen <claude@mathr.co.uk> wrote:

Hi Simon,

On 04/08/16 09:54, Simon Iten wrote:

ah sorry, yes

i want to read a wavetable, say 128 steps and calculate the gain structure to aproximate this wavetable with sine waves.
the idea behind this is to get a different sound from wavetables, use low resolution wavetables to get nice sounds (waldorf microwave xt)

so for a saw wave i would want the following numbers.

1 0.5 0.3333 0.25 0.2 and so on…

how to do this for an arbitrary input wavetable?

i looked at the fft examples but it is not clear to me how i would do this with a single wavetable (of known size)

You could do something like this with [rfft~], but you lose phase
information which might be important depending on what you are doing
(use fixed-width font to see diagram):

"set appropriate block size, turn off dsp, bang to execute 1 block"
|
[switch~]

[tabplay~ wavetable]
|
[rfft~ ]
^    ^
[*~] [*~]
 \  /
 [+~]
  |
 [sqrt~]
  |
 [tabsend~ spectrum]

or if there is a “simpler” (without fft) possibility that would be great.

I don't think you'll get simpler than FFT here.  As a bonus you can also
get phase information (sinesum has all phases 0, cosinesum all phases
pi/2, general wavetable can have arbitrary phases).

You could use [rifft~] instead of sinesum to generate your wavetable,
too.  Note there may be some issues with normalization (fft->ifft has an
amplitude gain equal to the blocksize, iirc).

For a more advanced use of oneshot FFT and IFFT for wave tables, see my
bandlimited project:
https://mathr.co.uk/blog/2015-02-12_bandlimited_wavetables.html


Claude
-- 
https://mathr.co.uk


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