[pd] hanning window + fft

[Kyle Klipowicz]

This is a good explanation.

~Kyle

On 9/4/06, Chuckk Hubbard <badmuthahubbard at gmail.com> wrote:

> If you did a FFT with a block size larger than an entire audio file,
> as I understand it, you wouldn't need a window.  Looping Martin Luther
> King's "I Have a Dream" speech (or the audio from the second season of
> CHIPS, or a recording of penguins in their natural habitat) over and
> over with a 30-minute pause between each round would technically be a
> "periodic function", so analyzing it this way would create an accurate
> representation; unfortunately, you would have exactly one value for
> each frequency, which tells you nothing about the frequency content at
> any point.
> To analyze changing frequency content, you have to take smaller
> blocks.  Repeating these to make them "periodic functions" means the
> beginning and end of any one block of sound will run together.  If
> this happens to create a continuous function, great, but the chances
> of that happening with every block are pretty low (if a block is 64
> samples, at 44100 samples per second, and the second season of CHIPS
> is 23 episodes, that's a lot of blocks).
> Windowing the input simply forces that part of the function to be
> continuous, by forcing beginning and end to the same value and
> direction.  To prevent the data from that part of the function from
> being completely lost, alternating FFTs can be taken with windows in
> opposite phase.
>
> I don't exactly understand what happens with the result, though.
> Whether the frequency values are averaged, or whether resynthesis is
> done with the same overlapping.  I also don't understand
> upsampling/downsampling with the block~ object, but I'm not sure
> that's related.
>
> -Chuckk
>
>
>
>
>
>
>
>
>
>
>
>
> >
> > Glad this came up!!
> > Kevin
> >
> >
> > _______________________________________________
> > PD-list at iem.at mailing list
> > UNSUBSCRIBE and account-management ->
> > http://lists.puredata.info/listinfo/pd-list
> >
> >
> >
>
>
> --
> "Far and away the best prize that life has to offer is the chance to
> work hard at work worth doing."
> -Theodore Roosevelt
>
> _______________________________________________
> PD-list at iem.at mailing list
> UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list
>


-- 

http://theradioproject.com
http://perhapsidid.blogspot.com

(((())))(()()((((((((()())))()(((((((())()()())())))
(())))))(()))))))))))))(((((((((((()()))))))))((())))
))(((((((((((())))())))))))))))))))__________
_____())))))(((((((((((((()))))))))))_______
((((((())))))))))))((((((((000)))oOOOOOO