Hi, Could someone recommend the best spectrum analysis software package - or method - for dealing with signals having only partial waves? I've been using SigView's FFT function on such signals, but the results are unexpected. I've tried applying filters/windows, varying the sample rate, and other things, but to no avail... If I pass in sustained signals comprising multiple wavelengths, e.g. from music (which I think is what SigView is tailored more towards anyway), the FFT works as expected: nice clean spikes at definite frequencies. But if I pass in a noisier waveform consisting of only partial waveforms (i.e. few component waves sustained for longer than 1 wavelength), the frequency amplitude response figures are much less clear. I'm thinking that the FFT function fundamentally is not the best method for our data. It may work well for sustained signals such as music notes, but not for the quickly-changing signals such as ours? FYI our data is in the 1 - 20 Hz range. I've heard of the Maximum Entropy (all poles) method, but SigView doesn't support that. Does anyone know whether I should be looking into alternatives to FFT? If FFT is the only way to go, however, perhaps there are other settings - e.g. windowing parameters - I could use? I am about to download and try SciLab - but don't know whether that offers additional methods to FFT... Many thanks in advance for any help with this! John
Spectrum analysis (FFT) of partial waves / scilab
Started by ●June 2, 2010
Reply by ●June 2, 20102010-06-02
Hi John, Just check with my FFT Spectrum Analyzer for the MS Windows platform using the free evaluation version... http://www.hpw-works.com Best regards Hanspeter Widmer ?
Reply by ●June 2, 20102010-06-02
On 2 juin, 18:46, "FatScouser" <john.hague@n_o_s_p_a_m.truebit.co.uk> wrote:> Hi, > > Could someone recommend the best spectrum analysis software package - or > method - for dealing with signals having only partial waves? I've been > using SigView's FFT function on such signals, but the results are > unexpected. I've tried applying filters/windows, varying the sample rate, > and other things, but to no avail... > > If I pass in sustained signals comprising multiple wavelengths, e.g. from > music (which I think is what SigView is tailored more towards anyway), the > FFT works as expected: nice clean spikes at definite frequencies. > > But if I pass in a noisier waveform consisting of only partial waveforms > (i.e. few component waves sustained for longer than 1 wavelength), the > frequency amplitude response figures are much less clear. > > I'm thinking that the FFT function fundamentally is not the best method for > our data. It may work well for sustained signals such as music notes, but > not for the quickly-changing signals such as ours? FYI our data is in the 1 > - 20 Hz range. > > I've heard of the Maximum Entropy (all poles) method, but SigView doesn't > support that. Does anyone know whether I should be looking into > alternatives to FFT? > > If FFT is the only way to go, however, perhaps there are other settings - > e.g. windowing parameters - I could use? > > I am about to download and try SciLab - but don't know whether that offers > additional methods to FFT... > > Many thanks in advance for any help with this! > > JohnYou may have a case more suited to harmonic inversion methods. Or spectral estimation. For the former, look at http://ab-initio.mit.edu/wiki/index.php/Harminv, for the later, a good book on DSP, oppenheim & schafer or proakis & manolakis.
Reply by ●June 2, 20102010-06-02
On 6/2/2010 12:46 PM, FatScouser wrote:> Hi, > > Could someone recommend the best spectrum analysis software package - or > method - for dealing with signals having only partial waves?... What is a partial wave? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●June 2, 20102010-06-02
On 6/2/2010 2:20 PM, Jerry Avins wrote:> On 6/2/2010 12:46 PM, FatScouser wrote: >> Hi, >> >> Could someone recommend the best spectrum analysis software package - or >> method - for dealing with signals having only partial waves? > > ... > > What is a partial wave? > > JerryThis is my first thought: http://www.youtube.com/watch?v=-TpW8xa0A-w then maybe this: http://www.youtube.com/watch?v=o2ZICNCxR8w past that I'm not sure. -- Eric Jacobsen Minister of Algorithms Abineau Communications http://www.abineau.com
Reply by ●June 3, 20102010-06-03
>On 6/2/2010 12:46 PM, FatScouser wrote: >> Hi, >> >> Could someone recommend the best spectrum analysis software package -or>> method - for dealing with signals having only partial waves? > > ... > >What is a partial wave? > >Jerry >-- >Engineering is the art of making what you want from things you can get. >����������������������������������������������������������������������� >Hi Jerry, Yeah - am maybe being contradictory there... To give an example: If you use SigView (with its default settings, i.e. no windows, zero padding, or averaging) to analyse a periodic sine with 4 wavelengths, say, you get a nice spike in the spectrum at expected frequency. But if you feed in a 'partial' sine wave, i.e. non-periodic 1 wavelength or less, said spike doesn't show. I guess attempting to fourier transform - which assumes periodicity - is like trying to push a square peg through a round hole, so I shouldn't be surprised. I just don't know at this stage the correct method to use. Cheers, John
Reply by ●June 3, 20102010-06-03
>On 6/2/2010 2:20 PM, Jerry Avins wrote: >> On 6/2/2010 12:46 PM, FatScouser wrote: >>> Hi, >>> >>> Could someone recommend the best spectrum analysis software package -or>>> method - for dealing with signals having only partial waves? >> >> ... >> >> What is a partial wave? >> >> Jerry > >This is my first thought: > >http://www.youtube.com/watch?v=-TpW8xa0A-w > >then maybe this: > >http://www.youtube.com/watch?v=o2ZICNCxR8w > >past that I'm not sure. > >-- >Eric Jacobsen >Minister of Algorithms >Abineau Communications >http://www.abineau.com >Very droll .. ;o)))
Reply by ●June 3, 20102010-06-03
On Jun 3, 10:26�am, "FatScouser" <john.hague@n_o_s_p_a_m.truebit.co.uk> wrote:> If you use SigView (with its default settings, i.e. no windows, zero > padding, or averaging) to analyse a periodic sine with 4 wavelengths, say, > you get a nice spike in the spectrum at expected frequency. > > But if you feed in a 'partial' sine wave, i.e. non-periodic 1 wavelength or > less, said spike doesn't show. > > I guess attempting to fourier transform - which assumes periodicity - is > like trying to push a square peg through a round hole, so I shouldn't be > surprised. I just don't know at this stage the correct method to use.The method depends on the goal. 'Frequency content' is *defined* by the Fourier transform. If you send in one wavelength of a sine wave in signal of total length more than one wavelength, then the frequency content is not just that of the sine wave from which you 'cut' the wavelength. The 'cutting' process itself introduces an infinite number of other frequencies. Equally, if you feed in less than one wavelenght of a sine wave, then you implicitly have a jump at the boundary due to lack of periodicity, and again you are introducing an infinite number of other frequencies. If you wish to define 'frequency content' differently, you can do so, and then analyse your signals appropriately. But this definition is up to you, and doubtless depends on your ultimate goal, i.e. the application, which you have not described. It may be connected to prior information about some 'total' signal of which you possess knowledge of only a part, or it may simply be a definition of your choice. illywhacker;
Reply by ●June 3, 20102010-06-03
Dnia 03-06-2010 o 10:26:51 FatScouser <john.hague@n_o_s_p_a_m.truebit.co.uk> napisał(a): (...)> I guess attempting to fourier transform - which assumes periodicity(...) There is no such assumption. This transform is decomposition within periodic signals. Maybe other transforms would fit to what you expect.> I just don't know at this stage the correct method to use.Are you looking for periodic component in energy signal (finite time and amplitude - relatively short and strange shaped impulse :))? Hmm, why? Their's spectrum is infinite which means energy is smashed to all frequencies because of discontinuity in time. So you will find no spikes but smooth fields. The ultimate question is do you know what are you looking for? -- Mikolaj
Reply by ●June 3, 20102010-06-03
On Jun 2, 5:20�pm, Jerry Avins <j...@ieee.org> wrote:> On 6/2/2010 12:46 PM, FatScouser wrote: > > > Hi, > > > Could someone recommend the best spectrum analysis software package - or > > method - for dealing with signals having only partial waves? > > � �... > > What is a partial wave? > > Jerry > -- > Engineering is the art of making what you want from things you can get.My 1st thought is "partial wave expansion" in physics. This has to do with the scattering of a plane wave by a particle where the resulting scattered wave is expressed as a sum of spherical waves each with its own amplitude and phase shift. But I'm quite sure the OP didn't want this version. LOL. Clay
