Could someone give me a reality check on something?

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Could someone give me a reality check on something?

Postby Consul » Thu Feb 28, 2008 10:29 pm

Okay, say you're doing a real-time FFT on an input signal. It doesn't matter what it might be at the moment. An FFT, if I read all of the descriptions correctly (I'm going by what my copy of the Csound Book tells me), basically splits a time-domain signal up into a (fairly large) number of bins across the frequency domain, with the strength of the signal for that slice of the frequency domain contained within each bin.

First off, how often is that amplitude-per-bin information updated? (I would assume it updates at the audio rate, otherwise you're losing a lot of information). This is a digression, though, and not really a part of the point of this post.

Now, in-between the FFT and its inverse, you can manipulate those bins directly. Which means that multiplying a selection of bins by a coefficient, perhaps determined by a cubic curve or something even more interesting? Also, if you wanted, couldn't one add information to bins that contain very little or no info at all?

In theory, with fine-grained enough bins, you could simulate just about any kind of filter in existence.

Here's another thought I've had: Could one do an FFT on a signal, and then do the inverse several times across smaller ranges of bins, ie, split 1024 bins into four sets of 256, and get four new signals separated by frequency? Just how atomic can one get with FFT?

Thanks for the help!
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Re: Could someone give me a reality check on something?

Postby lowkey » Fri Feb 29, 2008 12:31 am

Basically we live in FFT world. It's used for a surprising amount of stuff. If you can think of an application it's most likely used for it.
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Re: Could someone give me a reality check on something?

Postby Consul » Fri Feb 29, 2008 4:30 pm

Okay, stupid me, rather than hitting the "quote" button to reply to cuse's reply to me, managed to hit "Edit" instead, and I ended up screwing up his reply to me. Maybe I shouldn't have mod powers after all. I PM'd cuse with an apology, but nevertheless, his post answered my questions, so thank you, cuse. :)

Rather than leaving my edit in place, which looked like what my reply instead should have, I deleted it.
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Re: Could someone give me a reality check on something?

Postby cuse » Sat Mar 01, 2008 2:35 pm

You always have the edit capability on your own posts, no matter if you have moderator permssions or not. So it wouldn't have been a difference.
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Re: Could someone give me a reality check on something?

Postby dahnielson » Sat Mar 01, 2008 2:49 pm

cuse wrote:You always have the edit capability on your own posts, no matter if you have moderator permssions or not. So it wouldn't have been a difference.


Yes, but he edited your informative reply (with the power as moderator) instead of his own and is now kicking himself for it. ;)
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Re: Could someone give me a reality check on something?

Postby Consul » Sat Mar 01, 2008 4:50 pm

It was a case of my stupidly clicking the wrong button, "Edit" instead of "Quote". I had intended to quote your reply to me, cuse, in a post, and instead ended up editing your post. D'OH! I didn't even notice what I was doing because the text of your post appeared in my browser pretty much as it should have. I'll definitely have to be more careful. Anyway, sorry about that.
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Re: Could someone give me a reality check on something?

Postby cuse » Sun Mar 02, 2008 2:13 pm

Aah, hahaha, I see ... :)
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