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Fourier analysis & adding harmonics
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audiodef



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PostPosted: Mon May 27, 2013 6:40 pm    Post subject: Fourier analysis & adding harmonics
Subject description: Experimentation advice sought
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I'm doing some experimentation and for that, I want to:

1. Filter out everything above a certain frequency (probably 250 Hz). This is easy enough.

2. Deconstruct the signal as much as possible. I'm thinking Fourier analysis.

3. For each single frequency present, add n number of harmonics at amplitudes yet to be determined.

4. Mix that back into the original signal.

This isn't the experiment - just something I want to do as part of it. I figure you guys might know some way to make these steps happen.

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Cynosure
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PostPosted: Tue May 28, 2013 3:44 am    Post subject: Reply with quote  Mark this post and the followings unread

You want to remove harmonics, and then add them bqck again? why not just leave them there to begin with?

I think u might be able to do some of this with isotope Iris. You can get a ten day trial on their website.
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audiodef



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PostPosted: Tue May 28, 2013 6:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Oh, no, I don't want to remove harmonics. I want to add additional harmonics, but under very controlled circumstances. And to add a further point, the signal in question is actual music, not just a tone, patch or sound.
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PostPosted: Tue May 28, 2013 6:09 am    Post subject: Reply with quote  Mark this post and the followings unread

To add harmonics to a signal, just distort it. Maybe you should look into waveshaping. It is hard to work out exactly what you want to do though...
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PostPosted: Tue May 28, 2013 6:15 am    Post subject: Reply with quote  Mark this post and the followings unread

The low-pass filtering does remove harmonics, along with any high-frequency inharmonic signal components.

ChucK's audio analysis ugens would give you a way to operate in the frequency domain and then convert back. I haven't done that in ChucK, but I am sure folks on the ChucK mailling list have.

I did something along these lines to allow myself to sing in three-part harmony using a Max/MSP patch with an fft and ifft a few years back. Pure Data (PD) appears to have the required ugens, and like ChucK it is free.

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audiodef



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PostPosted: Tue May 28, 2013 6:39 am    Post subject: Reply with quote  Mark this post and the followings unread

Hm... I don't want to distort anything. The low-pass filtering would be just to remove everything above 250 Hz, harmonics and all. That's OK.

I figured I might be using ChucK or Supercollider or something like that.

I've been way too vague, and I'm sorry. I just didn't want to get boring. Razz

What I'm doing is experimenting with ways to make bass richer for people with cochlear implants who listen to music. See, bass is a bit thin. What I've found in some preliminary testing is that a fundamental frequency - a sine at 55 Hz - sounds noticeably fuller when I add two harmonics at 110 and 220 Hz with relative amplitudes of 1/4 and 1/8 (I started with the first harmonic being at a relative amplitude of 1/2, but that just resulted in octave unity). This was the perceived result with my implant.

So now I want to see if I can apply this by breaking down a music signal, filtering out the lowest fundamentals, and adding harmonics in the same way. If this does anything useful for perception, I can send this info to Advanced Bionics, and if they're so inclined, they can translate that into a future software upgrade for their external processors.

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[Q]



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PostPosted: Tue May 28, 2013 7:24 am    Post subject: Reply with quote  Mark this post and the followings unread

This should do it.. Smile

http://www.klingbeil.com/spear/

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audiodef



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PostPosted: Tue May 28, 2013 8:22 am    Post subject: Reply with quote  Mark this post and the followings unread

SPEAR looks very useful, thanks!

I was able to run it on WINE (although I had to upgrade to the latest unstable version to run it).

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