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using fft~ to modulate video?

August 22, 2010 | 2:05 pm

Hi guys,

I am working on a project at the moment and I want to analyse an audio signal and use it to modulate something I am making in jitter. I am a little out of my depth though… I basically want to be able to specify a frequency band to analyse (eg. bass frequencies 50hz to 150hz) and analyse its amplitude into a signal between -1. and 1. and then use that to modulate parameters of the visual patch I am making.

I think I need the fft~ object to analyse, and the capture object….but I don’t understand how to turn that into a constant signal…

I had a look at the fft~ tutorial and got quite lost :/ any advice anyone can give is GREATLY appreciated!


August 22, 2010 | 2:28 pm

a lowpassfilter or interpolator will be enough for this task.
average~, avg~, biquad~, sfv~, buffir~, fffb~, slide~ …..


August 22, 2010 | 2:30 pm

The thing is though, I want to be able to analyse multiple bands of the audio signal, but I don’t want to run a heap of objects that will chew up my processor….wouldn’t that rule out those objects, as I would need to run a whole bunch of them in parallel?


August 23, 2010 | 3:49 pm

I’ve posted up my FFT object here
http://www.andrewrobertson.net./research/maxmsp.html – it uses FFTW library and outputs the first 256 FFT values. It’s this part that you want:

"Here is a BasicFFT object with openFrameworks visualisation that will output the raw FFT data. It’s sent by osc to openFrameworks. The full openFrameworks project is full Xcode openFrameworks Project is here."

Anything you need to get working, let me know.

Andrew


August 24, 2010 | 4:07 am

Thanks very much Andrew, that looks helpful. The nuts and bolts behind the fft object are still a bit confusing to me, but hopefully this will clear it up a bit. Thanks again mate!


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