[FFT] Why is the performance so important?

On Mon, 14 Nov 2011 17:42:53 +0200, Tauno Voipio
<tauno.voipio@notused.fi.invalid> wrote:

    [Snipped by Lyons]
>
>Get a good book, e.g.
>
>  Richard G. Lyons, Understanding Digital Signal Processing
>
>read and understand it, and return with follow-up questions
>after that.

Hello Tauno,
   if you send an E-mail to me telling me 
which Edition, and which Printing Number, of my
book that you have, I'll send you the book's errata.

See Ya',
[-Rick-]
 

I'm an audio guy, but one possible application would be texture
recognition in images. This requires a 2-D FFT, and scale that to any
reasonably sized image, and you can see where having a *very* tight
FFT would be critical.

On Nov 14, 9:23&#4294967295;am, "Caspian" <matrose@n_o_s_p_a_m.me.com> wrote:
> >Caspian wrote:
>
> >> Hello DSP pros,
>
> >> I'm currently working on an optimized version of FFT for ARM NEON.
> (FHT,
> >> to be exact.)
>
> >> I'm neither a DSP specialist nor mathematician, and it was very hard
> for
> >> me to understand the way FFT works.
>
> >> Now it's about 50% done, and I have my doubt about this : "What's the
> use
> >> of this? What does it bring when my FFT runs 20times faster than some
> >> unnamed opensource ones on handhelds?"
>
> >If you don't know why performance is important than it's probably not
> important.
> >If you do this work because someone asked you to do it than you must ask
> this
> >person why it pays you to improve performance.
>
> >> I really don't see any point int this. Maybe because I know too little
> >> about DSP.
>
> >Better performance could reduce power consumption.
>
> >bye
> >Andreas
> >--
> >Andreas H nnebeck | email: a...@gmx.de
> >----- privat ---- | www &#4294967295;:http://www.huennebeck-online.de
> >Fax/Anrufbeantworter: 0721/151-284301
> >GPG-Key:http://www.huennebeck-online.de/public_keys/andreas.asc
> >PGP-Key:http://www.huennebeck-online.de/public_keys/pgp_andreas.asc
>
> Usually I'm the one in the company asking for the last bit of performance.
> :)
> I've been working mostly on graphics and image processing where the
> performance increases were literally visible.
>
> But FFT..... I simply know too little about its field of application.
>
> Any idea where heavily FFT'ing large blocks would be necessary on
> handhelds?
>
> cya
>
> PS : Deutsch kann ich auch, sogar besser als Englisch. Die sind aber beide
> Fremdsprachen fuer mich. Vielen Dank.

On Mon, 14 Nov 2011 07:22:46 -0600, Caspian wrote:
> I'm currently working on an optimized version of FFT for ARM NEON. (FHT,
> to be exact.)
> 
> I'm neither a DSP specialist nor mathematician, and it was very hard for
> me to understand the way FFT works.
> 
> Now it's about 50% done, and I have my doubt about this : "What's the
> use of this? What does it bring when my FFT runs 20times faster than
> some unnamed opensource ones on handhelds?"
> 
> I really don't see any point int this. Maybe because I know too little
> about DSP.
> 
> Could someone enlighten me? It would be really great to be motivated
> again.

Many of the machines with ARM chips in them spend a lot of their time 
playing (or, sometimes, recording) music, or watching videos.  Most of 
the popular audio codecs operate in the frequency domain (usually MDCT or 
CQMF or both), so decoding those bitstreams always finishes with a 
frequency->time domain transform.  Most such transforms can be expressed 
as twiddles around FFT routines, so if you have a fast FFT you also have 
a fast MDCT or CQMF or whatever.  Since the transform part of a decoder 
usually represents a good 30% or more of the work required for the 
decode, shaving a lump of that off will translate directly to extended 
battery life for the media-consuming device user.  Go nuts!

Cheers,

-- 
Andrew

Thank you very much, all of you.

Vielen Dank an euch alle. :)