FFT Analysis for Dummies Options

[Ethan Winer]

Folks,

I'd like to learn more about FFTs. I'm not a math guy, so I imagine I'll never fully understand all the nuances. But I'd like to try anyway. I understand the general concept, that an FFT shows how much energy is present at different frequencies. What I'd like to know is how to set the various parameters such as FFT Size and Overlap, when to use the different types of window smoothing and why, and so forth. Below is a list of settings in the Rightmark FFT analyzer with my associated questions, and hopefully this is a good place to start.

FFT Size: I understand that the higher the number, the better the frequency resolution. So why is this
even adjustable? Why not just use the highest resolution possible automatically?

Zero Padding: This ranges from None through 8x. What does this do?

FFT Overlap: What is this for, and when would you use higher or lower values?

FFT Window: I recognize some of the names, but have no idea when or why one would select these choices.

Kaiser Window beta: I have no idea what this does either.

I noticed that Sound Forge lets you pick the number of slices to show. What are slices and why is more than
one needed to analyze a Wave file?

I realize this is a lot to ask! If anyone knows of a good newbie-level tutorial that explains this in plain English with minimal math, I'd love to see it. Everything I've found through Google starts right in with math that's way over my head.

--Ethan

[Woodinville]

So, Ethan, did you run some of the scripts yet?

Note, in order to use the script "crunch" you need to record the "swisha" signal put out through a speaker to a mic, in channel 1, and loopback the DAC to channel two, so you have a stereo signal with the system response in one channel and the stimulus in the second channel. Save this as "foo.wav".

You need to record at least 23 seconds more or less centered on the "swisha" signal.

Make sure you don't clip or anything.

When you have a reference, move "foo.wav" to "bar.wav" and put your new measurements in foo.wav and then run crunch3, and you get to see the differences.

[Ethan Winer]

So, Ethan, did you run some of the scripts yet?

No, I don't have any way to do anything useful with those files. By "deck" I thought this was a Power point show I could learn from.

--Ethan

[Woodinville]

So, Ethan, did you run some of the scripts yet?

No, I don't have any way to do anything useful with those files. By "deck" I thought this was a Power point show I could learn from.

--Ethan

You can upload octave for free for apple, linux, or windows. So yes, you can get a way to do it.

Ditto audacity.

Ditto gvim.

Then you can design your own scripts.

There are a couple of powerpoint decks, too, of course. But you want to upload octave (instructions at www.aes.org/sections/pnw very soon if not now) and actually play with this stuff.

[Ethan Winer]

Hey, I watched an FFT tutorial "webinar" put on by Prism Sound today, and it was excellent. It was aimed at non-math people like me, and I learned a lot. They said it will be on their web site in about a week for all to see. If anyone cares I'll post a link when it's up.

--Ethan

[xnor]

If anyone cares I'll post a link when it's up.

I care.

[C.R.Helmrich]

Me too. To many people, such a resource will be more helpful than an .m file and the instruction to download Octave. After all, this thread is called "FFT Analysis for Dummies"...

Chris (thinking of - maybe one day - making an explanatory Youtube video on the DFT)