Hello Everybody :) I'd like to refer to opinion more expirienced people about spectral leakage. Part of my task which is related with DSP course is to tell about it to rest of the class. While I (think I) have sufficient knowledge and resources to do regular work ;), i don't have any idea about what extra thing i can tell about - particulary, if spectral leakage can be useful in anyway, so i decided to ask for a piece of advice here. Any suggestions are most welcome :) Best Regards, Peter
[question] spectral leakage - is it ONLY a problem ?
Started by ●March 21, 2005
Reply by ●March 21, 20052005-03-21
>Hello Everybody :) > >I'd like to refer to opinion more expirienced people about >spectral leakage. Part of my task which is related with DSP >course is to tell about it to rest of the class. While I (think I) have >sufficient knowledge and resources to do regular work ;), i don't have >any idea about what extra thing i can tell about - particulary, if >spectral leakage can be useful in anyway, so i decided to ask >for a piece of advice here. Any suggestions are most welcome :) > > >Best Regards, >Peter >In none of the applications I have used it for have I ever seen a benefit. That and smearing are not too fondly looked upon. I would not know if it had a positive effect because it is based on imperfections in the sampling method (incorrect term I know but the word escapes me as I quickly write this)itself, namely the windowing or weighting used. If i remember correctly (and i should or i will reply with a very embarrassed apology) leakage occurs when the window allows power from bands of the frequency domain of the true PSD to overflow onto areas that are supposed to be zero. Leaking power to bands that should not have them. I do not really think it is useful sorry...but maybe I am wrong. sincerely, Crim This message was sent using the Comp.DSP web interface on www.DSPRelated.com
Reply by ●March 21, 20052005-03-21
Antey wrote:> Hello Everybody :) > > I'd like to refer to opinion more expirienced people about > spectral leakage. Part of my task which is related with DSP > course is to tell about it to rest of the class. While I (think I) have > sufficient knowledge and resources to do regular work ;), i don't have > any idea about what extra thing i can tell about - particulary, if > spectral leakage can be useful in anyway, so i decided to ask > for a piece of advice here. Any suggestions are most welcome :) > > > Best Regards, > PeterSpectral leakage in a Fourier transform is like the blurring of an out-of-focus lens. Soft-focus lenses are sometimes used for portraits of people with skin blemishes. I can think of no corresponding use in data analysis. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●March 21, 20052005-03-21
"Jerry Avins" <jya@ieee.org> wrote in message news:-fWdnTewxuSreaPfRVn-gQ@rcn.net...> Antey wrote: >> Hello Everybody :) >> >> I'd like to refer to opinion more expirienced people about >> spectral leakage. Part of my task which is related with DSP >> course is to tell about it to rest of the class. While I (think I) have >> sufficient knowledge and resources to do regular work ;), i don't have >> any idea about what extra thing i can tell about - particulary, if >> spectral leakage can be useful in anyway, so i decided to ask >> for a piece of advice here. Any suggestions are most welcome :) >> >> >> Best Regards, >> Peter > > Spectral leakage in a Fourier transform is like the blurring of an > out-of-focus lens. Soft-focus lenses are sometimes used for portraits of > people with skin blemishes. I can think of no corresponding use in data > analysis. > > Jerry > -- > Engineering is the art of making what you want from things you can get. > �����������������������������������������������������������������������Hi Antey ; using wikepedias definition of when spectral leakage occurs : http://en.wikipedia.org/wiki/Spectral_leakage I suppose you could use it as an indication that one of the things that cause spectral leakage has happened and maybe adjust your sampling accordingly. You'd need pretty good signal to noise to be able to do it with any confidence. Best of Luck - Mike
Reply by ●March 21, 20052005-03-21
>Antey wrote: >> Hello Everybody :) >> >> I'd like to refer to opinion more expirienced people about >> spectral leakage. Part of my task which is related with DSP >> course is to tell about it to rest of the class. While I (think I) have>> sufficient knowledge and resources to do regular work ;), i don't have>> any idea about what extra thing i can tell about - particulary, if >> spectral leakage can be useful in anyway, so i decided to ask >> for a piece of advice here. Any suggestions are most welcome :) >> >> >> Best Regards, >> Peter > >Spectral leakage in a Fourier transform is like the blurring of an >out-of-focus lens. Soft-focus lenses are sometimes used for portraits of>people with skin blemishes. I can think of no corresponding use in data >analysis. > >Jerry >-- >Engineering is the art of making what you want from things you can get. >����������������������������������������������������������������������� >Unless of course...you want to deliberatly drown out a weak signal in a spectral band ;). But that would be rather silly, wouldn't it. I think of spectral leakage (and smearing for that matter) as a mirage. you can't tell if it is really there or it is your eyes tricking you, horrible analogy but i thought it sounded rather right. --Crim This message was sent using the Comp.DSP web interface on www.DSPRelated.com
Reply by ●March 21, 20052005-03-21
Jerry Avins wrote:> > Spectral leakage in a Fourier transform is like the blurring of an > out-of-focus lens. Soft-focus lenses are sometimes used for portraitsof> people with skin blemishes. I can think of no corresponding use indata> analysis. >Hello Jerry, This can be useful for data trending. My late father who was a statistician, said that sometimes when all else fails, you just print out the numbers and squint at the printout to see if there is a trend. Clay
Reply by ●March 21, 20052005-03-21
Clay wrote:> Jerry Avins wrote: > >>Spectral leakage in a Fourier transform is like the blurring of an >>out-of-focus lens. Soft-focus lenses are sometimes used for portraits > > of > >>people with skin blemishes. I can think of no corresponding use in > > data > >>analysis. >> > > > Hello Jerry, > This can be useful for data trending. My late father who was a > statistician, said that sometimes when all else fails, you just print > out the numbers and squint at the printout to see if there is a trend. > > ClayI can see that. It's interesting to speculate about the meaning of low-pass filtering the graph of a spectrum. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●March 21, 20052005-03-21
"Jerry Avins" <jya@ieee.org> wrote in message news:goudnejSHLaKm6LfRVn-sQ@rcn.net...> Clay wrote: > > Jerry Avins wrote: > > > >>Spectral leakage in a Fourier transform is like the blurring of an > >>out-of-focus lens. Soft-focus lenses are sometimes used for portraits > > > > of > > > >>people with skin blemishes. I can think of no corresponding use in > > > > data > > > >>analysis. > >> > > > > > > Hello Jerry, > > This can be useful for data trending. My late father who was a > > statistician, said that sometimes when all else fails, you just print > > out the numbers and squint at the printout to see if there is a trend. > > > > Clay > > I can see that. It's interesting to speculate about the meaning of > low-pass filtering the graph of a spectrum.Isn't low-pass filtering the graph of a spectrum just 'video filtering or video bandwidth filtering'...something that's used fairly extensively in spectrum analyzers? I will admit that this term is usually not used in the world of 'FFT spectrum analyzers'. Cheers Bhaskar> > Jerry > -- > Engineering is the art of making what you want from things you can get. > �����������������������������������������������������������������������
Reply by ●March 21, 20052005-03-21
Bhaskar Thiagarajan wrote: ...> Isn't low-pass filtering the graph of a spectrum just 'video filtering or > video bandwidth filtering'...something that's used fairly extensively in > spectrum analyzers? I will admit that this term is usually not used in the > world of 'FFT spectrum analyzers'.I didn't mean low-pass filtering the signal. I meant taking the bin heights as samples of a new signal, and low-pass filtering that. The peaks would come down and the empty bins between them would rise. I can (by squinting) see what it looks like. What it means is another matter. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●March 21, 20052005-03-21
"Jerry Avins" <jya@ieee.org> wrote in message news:9didnSZTe8gGraLfRVn-2Q@rcn.net...> Bhaskar Thiagarajan wrote: > > ... > > > Isn't low-pass filtering the graph of a spectrum just 'video filteringor> > video bandwidth filtering'...something that's used fairly extensively in > > spectrum analyzers? I will admit that this term is usually not used inthe> > world of 'FFT spectrum analyzers'. > > I didn't mean low-pass filtering the signal. I meant taking the bin > heights as samples of a new signal, and low-pass filtering that. The > peaks would come down and the empty bins between them would rise. I can > (by squinting) see what it looks like. What it means is another matter.That's what I meant as well Jerry. 'Video' filtering refers to filtering the 'video' or 'trace' data rather than the input signal. Typically it is used to smooth out noise to try and identify spurs, but it has the same effect as you mention. Some variations do exist in video filtering...some refer to this term when several traces are averaged together while others use this when each trace is sent through a low pass filter. Cheers Bhaskar> > Jerry > -- > Engineering is the art of making what you want from things you can get. > �����������������������������������������������������������������������
