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

# The system that requires largest!

Started by ●December 20, 2003

Reply by ●December 20, 20032003-12-20

santosh.nath@ntlworld.com (santosh nath) wrote in message news:<6afd943a.0312201539.555ad3a6@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

Reply by ●December 21, 20032003-12-21

Hello Santosh, I think Lake DSP uses extremely long FIR filters. Something like thousands if not tens of thousands of taps. Clay "santosh nath" <santosh.nath@ntlworld.com> wrote in message news:6afd943a.0312201539.555ad3a6@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

Reply by ●December 21, 20032003-12-21

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?

Reply by ●December 21, 20032003-12-21

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

Reply by ●December 21, 20032003-12-21

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, > santoshWhat'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. �����������������������������������������������������������������������

Reply by ●December 21, 20032003-12-21

On 20 Dec 2003 15:39:58 -0800, santosh.nath@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, >santoshHi, 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-]

Reply by ●December 21, 20032003-12-21

On Sun, 21 Dec 2003 02:20:58 -0600, Richard Owlett <rowlett@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-]

Reply by ●December 21, 20032003-12-21

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. �����������������������������������������������������������������������

Reply by ●December 21, 20032003-12-21

Rick Lyons wrote:> On Sun, 21 Dec 2003 02:20:58 -0600, Richard Owlett > <rowlett@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.