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Discussion Groups | Comp.DSP | The system that requires largest!

There are 30 messages in this thread.

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The system that requires largest! - santosh nath - 2003-12-20 18:39:00

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


Re: The system that requires largest! - Oliver Faust - 2003-12-20 22:21:00

s...@ntlworld.com (santosh nath) wrote in message news:<6...@posting.google.com>...
> 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)?.
> 

Hi,
I can only state the number of FFT points for the OFDM (Orthogonal
Frequency Division Multiplex) modulation scheme used in digital
broadcasting. Terrestrial Digital Video Broadcasting (DVB) uses up to
4096 point FFTs.
You can find a high order QAMs also in DVB but this time for cable
transmission. From what I know they encode up to eight bits for one
symbol resulting in a 256QAM.
You require a large number of filter coefficients if you want to alter
the sample frequency of a signal. For a direct implementation these
interpolation filters can have 100 or even 200 over taps. But
sophisticated implementation techniques, (poly phase decomposition for
interpolation as example), are used to reduce the number of taps for
these filters.

Oliver Faust


Re: The system that requires largest! - Clay S. Turner - 2003-12-21 00:47:00

Hello Santosh,

I think Lake DSP uses extremely long FIR filters. Something like thousands
if not tens of thousands of taps.

Clay


"santosh nath" <s...@ntlworld.com> wrote in message
news:6...@posting.google.com...
> 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


newbie question inspired by Re: The system that requires largest! - Richard Owlett - 2003-12-21 03:20:00

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)?
> 

I'm using an ~22050 point fft to look at .5 sec chunks of speech.

> 
>  Real time constraint should be applied if needed.
> 

Definitely not real time.
Data source is CD.
Calculations done in Scilab on a PC with a Gig of memory.
Therefore "brute force" methods are acceptable.

Question:

Someone recently pointed out how long time chunks could be built up 
from overlapping ifft's. Is there a similar method going from time 
domain -> freq domain? [ Seems it there should by as lots of other 
things are symmetrical. ] [ My current frequency range of interest is 
continuous from 20 Hz to 5 kHz. ]

Also, later I suspect I will want to compare spectra of data with 
different window widths while having the same resolution in the 
frequency domain. Each spectrum will be "normalized against itself", 
either by saying the largest peak or the value at a certain frequency 
is 0 dB. How?


Re: The system that requires largest! - Bob Cain - 2003-12-21 12:11:00

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)?

I have seen, but failed to bookmark, an application that
will do a single FFT of an arbitrary length audio file. 
Wish I could be more helpful as to where to locate it.


Bob
-- 

"Things should be described as simply as possible, but no
simpler."

                                             A. Einstein


Re: The system that requires largest! - Jerry Avins - 2003-12-21 12:43:00

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

What's with the preoccupation with biggest and mostest? Financial 
analysts perform FFTs and transversal FIRs using tens of thousands of 
bins and taps. I haven't kept track of the actual numbers.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯


Re: The system that requires largest! - Rick Lyons - 2003-12-21 13:31:00

On 20 Dec 2003 15:39:58 -0800, s...@ntlworld.com (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

Hi,

  years ago I was performing 4 million-point 
FFTs on a Sun Workstation using MATLAB.
I was generating test signals for some others 
to use in testing their DSP algorithms.

I'll bet someone here will probably know 
of a larger-sized FFT application.

Don't the SETI people (looking for little 
green men) use million-point FFTs?

Also, doesn't one of those commercial 
up/down converter chips (Analog devices, 
of Harris/Intersil, GreyChip) have 
a 256-tap FIR filter built in?

Merry Xmas,
[-Rick-]


Re: newbie question inspired by Re: The system that requires largest! - Rick Lyons - 2003-12-21 13:48:00

On Sun, 21 Dec 2003 02:20:58 -0600, Richard Owlett
<r...@atlascomm.net> wrote:

>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)?
>> 
>
>I'm using an ~22050 point fft to look at .5 sec chunks of speech.
>
>> 
>>  Real time constraint should be applied if needed.
>> 
>
>Definitely not real time.
>Data source is CD.
>Calculations done in Scilab on a PC with a Gig of memory.
>Therefore "brute force" methods are acceptable.
>
>Question:
>
>Someone recently pointed out how long time chunks could be built up 
>from overlapping ifft's. Is there a similar method going from time 
>domain -> freq domain? [ Seems it there should by as lots of other 
>things are symmetrical. ] [ My current frequency range of interest is 
>continuous from 20 Hz to 5 kHz. ]
>
>Also, later I suspect I will want to compare spectra of data with 
>different window widths while having the same resolution in the 
>frequency domain. Each spectrum will be "normalized against itself", 
>either by saying the largest peak or the value at a certain frequency 
>is 0 dB. How?

Hi Richard,
  Humm, I didn't understand your last question.
Different window widths (i.e., the length of 
your time sequences) will result in different 
freq-domain resolutions.  That's assuming the sample 
rate is the same for the various time-domain sequences.

You can plot spectra where the largest spec magnitude 
sample is always at 0 dB by:

  1) compute your FFT samples, X(m);
  2) compute the magnitudes of your FFT results, |X(m)|;
  3) find the largest magnitude sample in the |X(m)|
     sequence, call that value "|X(m)|max";
  4) divide the |X(m| sequence by the |X(m)|max value to 
     yield a "normalized" sequence, call that sequence 
     "|X(m)|norm";
  5) plot 20*log10 of sequence "|X(m)|norm".

The peak |X(m)| value will always be at the 0 dB level, 
and all other spectral mag samples will be at 
negative dB levels.  This makes it easier to compare 
two spectra shapes (two spectral envelopes).

See Ya'
[-Rick-]


Re: The system that requires largest! - Jerry Avins - 2003-12-21 14:28:00

Jerry Avins wrote:

> 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
> 
> 
> What's with the preoccupation with biggest and mostest? Financial 
> analysts perform FFTs and transversal FIRs using tens of thousands of 
> bins and taps. I haven't kept track of the actual numbers.

Correction: hundreds of thousands.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯


Re: newbie question inspired by Re: The system that requires largest! - Richard Owlett - 2003-12-21 15:14:00

Rick Lyons wrote:

> On Sun, 21 Dec 2003 02:20:58 -0600, Richard Owlett
> <r...@atlascomm.net> wrote:
> 
> 
>>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)?
>>>
>>
>>I'm using an ~22050 point fft to look at .5 sec chunks of speech.
>>
>>
>>> Real time constraint should be applied if needed.
>>>
>>
>>Definitely not real time.
>>Data source is CD.
>>Calculations done in Scilab on a PC with a Gig of memory.
>>Therefore "brute force" methods are acceptable.
>>
>>Question:
>>
>>Someone recently pointed out how long time chunks could be built up 
> 
>>from overlapping ifft's. Is there a similar method going from time 
> 
>>domain -> freq domain? [ Seems it there should by as lots of other 
>>things are symmetrical. ] [ My current frequency range of interest is 
>>continuous from 20 Hz to 5 kHz. ]
>>
>>Also, later I suspect I will want to compare spectra of data with 
>>different window widths while having the same resolution in the 
>>frequency domain. Each spectrum will be "normalized against itself", 
>>either by saying the largest peak or the value at a certain frequency 
>>is 0 dB. How?
> 
> 
> Hi Richard,
>   Humm, I didn't understand your last question.
> Different window widths (i.e., the length of 
> your time sequences) will result in different 
> freq-domain resolutions.  That's assuming the sample 
> rate is the same for the various time-domain sequences.
> 

Obvious now that you mention it ;{
How do you calculate the nominal center of each point in the spectrum?
[ I did a dimensional analysis of the formula I used and came up with 
trash ;[



> You can plot spectra where the largest spec magnitude 
> sample is always at 0 dB by:
> [snip]

At least I had that much right.


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