> Though it is not very good (rather stupid) to ask the following
> questions; I thought this could be a pre-Xmas fun!
>
> 1. What is the largest FFT size(point) ever used so far and
> where(Application)?
NASA has tech reports on doing out of core FFTs on Crays from the 1980's,
so assuming they have kept up, they would presently be doing several
billion point ffts at the very least.
>
>
> Enjoy your days with happy X-mas!!
> Cheers,
> santosh
--
Sander
+++ Out of cheese error +++
Reply by Steven G. Johnson●January 9, 20042004-01-09
Ray Andraka wrote:
> Oops, that should have been 4Giga point.
>
> Ray Andraka wrote:
>>Some time ago someone approached me about doing a 4M point FFT for an
>>astronomy application. It wasn't real time, and I suggested it would
>>be far cheaper doing it with PCs. Don't know what happened with the
>>project since.
We (FFTW authors) have received a number of notes from people doing
multi-billion point FFTs, and in fact this was the motivation for our
inclusion of parallel 1d distributed-memory FFTs in FFTW 2.x. Often,
it's not even time that makes people want to parallelize, it's memory
usage. (The same constraints originally motivated out-of-core FFTs,
although I don't hear about too many people using those any more.)
Typical applications for this sort of thing seem to be in astronomy, as
happened in your case. e.g. analyzing pulsar data, gravitational waves,
etcetera.
Cordially,
Steven G. Johnson
Reply by Ray Andraka●January 8, 20042004-01-08
Oops, that should have been 4Giga point.
Ray Andraka wrote:
> Some time ago someone approached me about doing a 4M point FFT for an
> astronomy application. It wasn't real time, and I suggested it would be
> far cheaper doing it with PCs. Don't know what happened with the project
> since. Large FIR filters are usually required because of a very narrow
> or sharp response. These are more efficiently realized using a polyphase
> or multi-rate approach, so in practice you'll usually find large filters
> broken down into a bank of smaller ones. I've done a number of filters,
> that if done in one stage would have numbered in the 100's of thousands of
> taps. Even if multi-rate approaches don't help, a filter that large is
> more efficiently done with fast convolution: ie in the frequency domain.
>
> santosh nath wrote:
>
> > Though it is not very good (rather stupid) to ask the following
> > questions; I thought this could be a pre-Xmas fun!
> >
> > 1. What is the largest FFT size(point) ever used so far and
> > where(Application)?
> > 2. What is the largest QAM constellation ever used commercially so far
> > and where(Application)? ?
> > 3. What is the largest FIR filter taps used so far and
> > where(Application)?.
> >
> > Real time constraint should be applied if needed.
> >
> > Enjoy your days with happy X-mas!!
> > Cheers,
> > santosh
>
> --
> --Ray Andraka, P.E.
> President, the Andraka Consulting Group, Inc.
> 401/884-7930 Fax 401/884-7950
> email ray@andraka.com
> http://www.andraka.com
>
> "They that give up essential liberty to obtain a little
> temporary safety deserve neither liberty nor safety."
> -Benjamin Franklin, 1759
--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email ray@andraka.com
http://www.andraka.com
"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759
Reply by Ray Andraka●January 8, 20042004-01-08
Some time ago someone approached me about doing a 4M point FFT for an
astronomy application. It wasn't real time, and I suggested it would be
far cheaper doing it with PCs. Don't know what happened with the project
since. Large FIR filters are usually required because of a very narrow
or sharp response. These are more efficiently realized using a polyphase
or multi-rate approach, so in practice you'll usually find large filters
broken down into a bank of smaller ones. I've done a number of filters,
that if done in one stage would have numbered in the 100's of thousands of
taps. Even if multi-rate approaches don't help, a filter that large is
more efficiently done with fast convolution: ie in the frequency domain.
santosh nath wrote:
> Though it is not very good (rather stupid) to ask the following
> questions; I thought this could be a pre-Xmas fun!
>
> 1. What is the largest FFT size(point) ever used so far and
> where(Application)?
> 2. What is the largest QAM constellation ever used commercially so far
> and where(Application)? ?
> 3. What is the largest FIR filter taps used so far and
> where(Application)?.
>
> Real time constraint should be applied if needed.
>
> Enjoy your days with happy X-mas!!
> Cheers,
> santosh
--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email ray@andraka.com
http://www.andraka.com
"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759
Reply by Rick Lyons●December 24, 20032003-12-24
On Mon, 22 Dec 2003 20:01:23 -0800, Bob Cain
<arcane@arcanemethods.com> wrote:
>
>
>Richard Owlett wrote:
>>
>> Obviously I asked WRONG question ;)
>>
>> Given (sample rate) AND (number of points in time domain)
>>
>> What is "frequency" of each point in FFT?
>>
>> Next question:
>> "Did I ask "right" question ;?
>
>If this is the answer: the difference in frequency between
>any two consecutive points of the transform is rate/#points.
>
>
>Bob
Yep,
If the sample rate is, say, 1 kHz and
you had eight samples, then the
spacing between FFT samples would be
1000/8 = 125 Hz.
The cyclic freq associated with the first
half of the FFT samples would be
FFT sample#: Freq:
0 0x125 = 0 Hz
1 1x125 = 125 Hz
2 2x125 = 250 Hz
3 3x125 = 375 Hz
etc. etc.
[-Rick-]
Reply by Rick Lyons●December 24, 20032003-12-24
On Mon, 22 Dec 2003 15:24:20 GMT, charles@pentek.com (Charles Krug)
wrote:
(snipped)
>
>
>Jerry, you have links for that?
>
>I ran a 4MB fft in LabView once. Started it, went to lunch, went to a
>long design review . . .
>
>Got back just in time (three hours on a 200MHz Pentium)
Hi,
Humm, ... three hours sure seems like
a long time. My 4,194,304-point (2^22)
FFTs sure didn't take that long using
MATLAB on a Sun workstation.
(I don't now the CPU clock rate.
That was in 1999.)
However, in the beginning I'd start my FFTs
and my machine would just go dead.
I finally realized I'd screwed up my indexing
and was trying to perform (2^22-1)-point
FFTs. Well, what I was doing was performing
(2^22-1)-point DFTs !!!!!!!!
That's why my machine appeared dead, it was
crunching away as fast as it could at an
almost impossibly-intensive computation.
[-Rick-]
Reply by Bob Cain●December 23, 20032003-12-23
Richard Owlett wrote:
>
> Obviously I asked WRONG question ;)
>
> Given (sample rate) AND (number of points in time domain)
>
> What is "frequency" of each point in FFT?
>
> Next question:
> "Did I ask "right" question ;?
If this is the answer: the difference in frequency between
any two consecutive points of the transform is rate/#points.
Bob
--
"Things should be described as simply as possible, but no
simpler."
A. Einstein
Reply by Allan Herriman●December 22, 20032003-12-22
On Mon, 22 Dec 2003 09:38:49 -0500, Jerry Avins <jya@ieee.org> wrote:
>Allan Herriman wrote:
>
> ...
>
>> I once made a 240 pole *analog* low pass filter.
>>
>> Regards,
>> Allan.
>
>That's amazing! (I assume it worked.)
Reply by Richard Owlett●December 22, 20032003-12-22
Obviously I asked WRONG question ;)
Given (sample rate) AND (number of points in time domain)
What is "frequency" of each point in FFT?
Next question:
"Did I ask "right" question ;?
Reply by Bhaskar Thiagarajan●December 22, 20032003-12-22
"Richard Owlett" <rowlett@atlascomm.net> wrote in message
news:vueinms39rld44@corp.supernews.com...
>
> I lurk on comp.lang.research .
> A frequent topic of discussion is detecting "silence" [ i.e. pauses
> between words/phrases/sentences ]
>
> Being one who talks a lot ;]
> I have a "gut" feel that *each* of those might be of fairly consistent
> duration for a particular speaker.
>
> Ignoring for the moment the current push for "real time"/"instant"
> recognition.
>
> Given a speech sample of tens of seconds, should/could/would an FFT of
> the *ENTIRE* utterance give indications of where and how long pauses were?
I don't think so.
The FFT of the entire sequence will only tell you (not sure exactly how) if
a certain frequency component existed (or didn't). It will not tell you
exactly when during the temporal record this occured. So in order to figure
*when* something happened (or didn't), you'd have to do FFTs on shorter
segments of the time data. Clearly you will be limited in terms of
resolution - you can only get one at a time...good time or frequency
resolution.
Hopefully some of that made sense.
Cheers
Bhaskar