On Mar 22, 9:35�am, "blackhermi" <dheeraj.iitm@n_o_s_p_a_m.gmail.com> wrote:> Hi > > I need to find out the frequencies present in the variation of a physical > quantity from a discretely sampled data of finite length. Which window (if > any) should I use? I think doing an fftn in MATLAB uses a rectangular > function by default. Please correct me if I am wrong. > > Also, is there a way to create a 2D version of a given window? > > Thanks and RegardsDo you know apriori how many frequencies are in the data? I.e., do you have a physical reason for there being n frequnecies in the data? Are the frequencies constant in time? Clay
Do I need a window?
Started by ●March 22, 2010
Reply by ●March 22, 20102010-03-22
Reply by ●March 22, 20102010-03-22
Rune Allnor wrote:> On 22 Mar, 15:25, Vladimir Vassilevsky <nos...@nowhere.com> wrote: > >>Rune Allnor wrote: >> >>>On 22 Mar, 15:14, Tim Wescott <t...@seemywebsite.now> wrote: >> >>>>Rune Allnor wrote: >> >>>"Why did you use the Gavrilovich-Cheng window? What properties >>>does that window offer that a regular window like, say, a Hann >>>window, does not?" >> >>Good idea. Nobody knows wtf is Gavrilovich-Cheng window, so everybody >>will will shut up so not to look as an idiot. > > I wouldn't play on human stupidity quite like that - there > is the chance that someone like Jerry or myself is in the > audiendce. In that case, the presenter will look like the > idiot. I know. I did ask that question, once upon a time > many years ago. Made a total fool - unintentionally! - of > the presenter when she had no answer to why she had made > some choise she had commented on during the presentation.Dr. Rune, did anybody (besides you and your vis-a-vis) realized what was it all about? Perhaps they were just annoyed that you woke them up from deep sleep.> If you want to play an insult, hide it in plain sight: Make > the obvious choise, but without justification. Or keep > quiet about the key trick while exanding on some triviality.Whether it was intended to be insult or not, I have no slightest idea about Gavrilovich-Cheng window. But I found Lanczos window in Wikipedia (how to spell Lanczos ?). They say it is absolutely the very best window and you must use it for all cases. VLV
Reply by ●March 22, 20102010-03-22
> > >Rune Allnor wrote: > >> On 22 Mar, 15:25, Vladimir Vassilevsky <nos...@nowhere.com> wrote: >> >>>Rune Allnor wrote: >>> >>>>On 22 Mar, 15:14, Tim Wescott <t...@seemywebsite.now> wrote: >>> >>>>>Rune Allnor wrote: >>> >>>>"Why did you use the Gavrilovich-Cheng window? What properties >>>>does that window offer that a regular window like, say, a Hann >>>>window, does not?" >>> >>>Good idea. Nobody knows wtf is Gavrilovich-Cheng window, so everybody >>>will will shut up so not to look as an idiot. >> >> I wouldn't play on human stupidity quite like that - there >> is the chance that someone like Jerry or myself is in the >> audiendce. In that case, the presenter will look like the >> idiot. I know. I did ask that question, once upon a time >> many years ago. Made a total fool - unintentionally! - of >> the presenter when she had no answer to why she had made >> some choise she had commented on during the presentation. > >Dr. Rune, did anybody (besides you and your vis-a-vis) realized what was >it all about? Perhaps they were just annoyed that you woke them up from >deep sleep. > >> If you want to play an insult, hide it in plain sight: Make >> the obvious choise, but without justification. Or keep >> quiet about the key trick while exanding on some triviality. > >Whether it was intended to be insult or not, I have no slightest idea >about Gavrilovich-Cheng window. But I found Lanczos window in Wikipedia >(how to spell Lanczos ?). They say it is absolutely the very best window >and you must use it for all cases.I thought Windows 7 was the very best window you must use in all cases. Steve
Reply by ●March 23, 20102010-03-23
On 23 Mar, 02:17, "steveu" <steveu@n_o_s_p_a_m.coppice.org> wrote:> >Rune Allnor wrote: > > >> On 22 Mar, 15:25, Vladimir Vassilevsky <nos...@nowhere.com> wrote: > > >>>Rune Allnor wrote: > > >>>>On 22 Mar, 15:14, Tim Wescott <t...@seemywebsite.now> wrote: > > >>>>>Rune Allnor wrote: > > >>>>"Why did you use the Gavrilovich-Cheng window? What properties > >>>>does that window offer that a regular window like, say, a Hann > >>>>window, does not?" > > >>>Good idea. Nobody knows wtf is Gavrilovich-Cheng window, so everybody > >>>will will shut up so not to look as an idiot. > > >> I wouldn't play on human stupidity quite like that - there > >> is the chance that someone like Jerry or myself is in the > >> audiendce. In that case, the presenter will look like the > >> idiot. I know. I did ask that question, once upon a time > >> many years ago. Made a total fool - unintentionally! - of > >> the presenter when she had no answer to why she had made > >> some choise she had commented on during the presentation. > > >Dr. Rune, did anybody (besides you and your vis-a-vis) realized what was > >it all about? Perhaps they were just annoyed that you woke them up from > >deep sleep. > > >> If you want to play an insult, hide it in plain sight: Make > >> the obvious choise, but without justification. Or keep > >> quiet about the key trick while exanding on some triviality. > > >Whether it was intended to be insult or not, I have no slightest idea > >about Gavrilovich-Cheng window. But I found Lanczos window in Wikipedia > >(how to spell Lanczos ?). They say it is absolutely the very best window > >and you must use it for all cases. > > I thought Windows 7 was the very best window you must use in all cases.I certainly need to change to a better window soon - water has been seeping in when weather was at its weatest this winter. Rune
Reply by ●March 28, 20102010-03-28
On Mon, 22 Mar 2010 07:14:08 -0700, Tim Wescott <tim@seemywebsite.now> wrote:>Rune Allnor wrote: >> On 22 Mar, 14:35, "blackhermi" <dheeraj.iitm@n_o_s_p_a_m.gmail.com> >> wrote: >>> Hi >>> >>> I need to find out the frequencies present in the variation of a physical >>> quantity from a discretely sampled data of finite length. Which window (if >>> any) should I use? >> >> It depends entirely on the data and what you attempt to do. >> If the SNR is large and the sinusoidals are well separated, >> then don't use any. If the SNR is low and you need to >> suppress side lobes, choose a window that can be tuned to >> your particular needs (the Kaiser window is just about the >> only one that fits that bill). Or avoid controversy by using >> the most popular window that everybody else use. I don't have >> any statistics, but the Hanning / Hann / von Hann window ought >> to end up among the top 3 in the popularity polls. > >Understanding the properties of the FFT would help, too -- that will let >you understand why you want to window the data, which in turn will help >you understand what window (if any) you want and why. > >While I could stand in front of a room of fellow engineers and defend a >choice of window by "it's popular _and_ it doesn't matter much anyway", >defending it with "'cause it's popular" would quite deservedly get me >laughed out of the room.Hi Tim, If someone asks me, "Why did you use the Hanning window in this application?", I typically answer with either, (1) "Because that's the way God wanted it to be.", or (2) "Because that's what the voices told me to use." See Ya', [Rick-]
Reply by ●March 29, 20102010-03-29
On 28 Mrz., 14:18, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote:> On Mon, 22 Mar 2010 07:14:08 -0700, Tim Wescott <t...@seemywebsite.now> > wrote: > > > > > > >Rune Allnor wrote: > >> On 22 Mar, 14:35, "blackhermi" <dheeraj.iitm@n_o_s_p_a_m.gmail.com> > >> wrote: > >>> Hi > > >>> I need to find out the frequencies present in the variation of a physical > >>> quantity from a discretely sampled data of finite length. Which window (if > >>> any) should I use? > > >> It depends entirely on the data and what you attempt to do. > >> If the SNR is large and the sinusoidals are well separated, > >> then don't use any. If the SNR is low and you need to > >> suppress side lobes, choose a window that can be tuned to > >> your particular needs (the Kaiser window is just about the > >> only one that fits that bill). Or avoid controversy by using > >> the most popular window that everybody else use. I don't have > >> any statistics, but the Hanning / Hann / von Hann window ought > >> to end up among the top 3 in the popularity polls. > > >Understanding the properties of the FFT would help, too -- that will let > >you understand why you want to window the data, which in turn will help > >you understand what window (if any) you want and why. > > >While I could stand in front of a room of fellow engineers and defend a > >choice of window by "it's popular _and_ it doesn't matter much anyway", > >defending it with "'cause it's popular" would quite deservedly get me > >laughed out of the room. > > Hi Tim, > � If someone asks me, "Why did you use the > Hanning window in this application?", > I typically answer with either, (1) "Because that's > the way God wanted it to be.", or (2) "Because that's > what the voices told me to use."Hi Rick My knee-jerk answer would be: "The guy's name was von Hann!" Regards, Andor
Reply by ●April 11, 20102010-04-11
On Mon, 29 Mar 2010 00:16:39 -0700 (PDT), Andor <andor.bariska@gmail.com> wrote:>On 28 Mrz., 14:18, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote: >> On Mon, 22 Mar 2010 07:14:08 -0700, Tim Wescott <t...@seemywebsite.now> >> wrote: >> >> >> >> >> >> >Rune Allnor wrote: >> >> On 22 Mar, 14:35, "blackhermi" <dheeraj.iitm@n_o_s_p_a_m.gmail.com> >> >> wrote: >> >>> Hi >> >> >>> I need to find out the frequencies present in the variation of a physical >> >>> quantity from a discretely sampled data of finite length. Which window (if >> >>> any) should I use? >> >> >> It depends entirely on the data and what you attempt to do. >> >> If the SNR is large and the sinusoidals are well separated, >> >> then don't use any. If the SNR is low and you need to >> >> suppress side lobes, choose a window that can be tuned to >> >> your particular needs (the Kaiser window is just about the >> >> only one that fits that bill). Or avoid controversy by using >> >> the most popular window that everybody else use. I don't have >> >> any statistics, but the Hanning / Hann / von Hann window ought >> >> to end up among the top 3 in the popularity polls. >> >> >Understanding the properties of the FFT would help, too -- that will let >> >you understand why you want to window the data, which in turn will help >> >you understand what window (if any) you want and why. >> >> >While I could stand in front of a room of fellow engineers and defend a >> >choice of window by "it's popular _and_ it doesn't matter much anyway", >> >defending it with "'cause it's popular" would quite deservedly get me >> >laughed out of the room. >> >> Hi Tim, >> � If someone asks me, "Why did you use the >> Hanning window in this application?", >> I typically answer with either, (1) "Because that's >> the way God wanted it to be.", or (2) "Because that's >> what the voices told me to use." > >Hi Rick > >My knee-jerk answer would be: "The guy's name was von Hann!" > >Regards, >AndorHi Andor, You are exactly correct. Regards, [-Rick-]
