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From: FatScouser on 2 Jun 2010 12:46
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
From: HpW on 2 Jun 2010 15:56
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

?


From: Zorg 421 on 2 Jun 2010 16:05
On 2 juin, 18:46, "FatScouser" <john.hague(a)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!
>
> John

You 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.
From: Jerry Avins on 2 Jun 2010 17:20
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.
�����������������������������������������������������������������������
From: Eric Jacobsen on 2 Jun 2010 17:54
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
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