Teaching and conducting research on DSP related topics for four decades. Robert Stockwell, I and Robert Lowe co-authored the defining paper on S-transform (ST), a method of local Fourier spectral analysis of time series. ST has been applied to 1-D (time series) and 2-D (images) in numerous and diverse fields including geophysics, medical imaging, power system quality studies, wind gust analysis etc.

Re: Spectrum monitoring - signal detection problem

Reply posted 3 weeks ago (01/04/2021)
Perhaps you can use a sliding DFT with the Goertzel algorithm and monitor in the frequency domain.  There are limitations of course. It will help if you can provide...
In applying the linear phase shift, you have to take into account the conjugate symmetry of the fft output.
The app looks neat and interesting.  But I need some description as to what the app illustrates.  Please point towards a tutorial on the subject.  Thanks.

Re: Off-topic: Xmas gift for a techie?

Reply posted 2 months ago (12/03/2020)
Thanks Neil.  I am going to order the book.  

Re: How to synthesize band-limited noise?

Reply posted 2 months ago (11/27/2020)
Hello Marcin:  If you do not have access to C/C++ libraries (like fft/ifft), the simplest method to generate a noise time series of length N, between frequencies...

Re: Purity > 1?

Reply posted 2 months ago (11/20/2020)
...

Re: Purity > 1?

Reply posted 2 months ago (11/19/2020)
If you have access to the input time series, you can apply FFT and get the specific Fourier component you calculate with Goertzel.  Do they differ by a factor?  Does...

Re: Purity > 1?

Reply posted 2 months ago (11/18/2020)
I think DTFT energy should be (1/N)*(DTFT)^2  .It all depends as to how DTFT is calculated.  Please compare the DTFT with the FFT output.  To obtain the Fourier...

Re: Purity > 1?

Reply posted 2 months ago (11/18/2020)
Please give some description  and expression for calculation of the purity.

Re: Constructing vector for IFFT

Reply posted 3 months ago (11/05/2020)
This thread started with discussion of zeropadding in the frequency domain and the consequent interpolation in the time domain.  The usage of the term 'interpolation'...

Re: Constructing vector for IFFT

Reply posted 3 months ago (11/05/2020)
The relationship between zero padding in t(or f) domain and interpolation between points in the f( or t) domain is exact.  Duality must hold.  One can look upon...

Re: Constructing vector for IFFT

Reply posted 3 months ago (11/05/2020)
Basically we have a set of digitised samples separated by gaps.  h = h(x0),h(x1),h(x2),...............h(xn)If one wishes to compute the value at a point xu within...

Re: Constructing vector for IFFT

Reply posted 3 months ago (11/05/2020)
One can interpolate by several methods.  The interpolated points by different methods give similar, but not identical results.  When referring to interpolation...

Re: Constructing vector for IFFT

Reply posted 3 months ago (11/04/2020)
I thought of another viewpoint that is (I think) is simpler.  When you add even a single zero point in the f domain (and mirror it), you are also increasing the...

Re: Constructing vector for IFFT

Reply posted 3 months ago (10/29/2020)
Zero padding is easier to understand for going from time > frequency domains.  Zero padding is adding more points, just that they are zeros.  The sample interval...

Re: Constructing vector for IFFT

Reply posted 3 months ago (10/27/2020)
1.  Let us your data series in the f domain is 1+N/2  points long.  You add the conjugate mirror points to get N points. Lets call this H2 Apply IFFT to the...

Re: Constructing vector for IFFT

Reply posted 3 months ago (10/26/2020)
Thanks for the sketch.  It made things a bit clearer.  But I need to understand some terms before I can give you an answer to your original question.  FFT is...

Re: Constructing vector for IFFT

Reply posted 3 months ago (10/26/2020)
Looks like you have an odd number of samples in the f domain.  sample s1=f0 denotes the DC term.  Then samples s2 to s281 represent s2=0.5Hz to s281=160Hz.  I...

Re: Anything like a “shift delay”?

Reply posted 3 months ago (10/24/2020)
I think you have to describe the query a little better.  I am assuming that x(t) is the input and y(t) the output of a filter.  What are the filter properties? ...
Let us consider a short vector A=[0 1 2 3 0] and a vector B (see matlab script below).  I have deliberately chosen the lengths of A (5) & B (21) as odd.  But...
I do not understand why you expect the crosscorrelation of y1 with different time series would give you the same peak value. Crosscorrelation is simply 'lag multiply...

Re: LFT

Reply posted 4 months ago (09/28/2020)
A basic assumption in applying FFT/IFFT (for that matter any operation on a sampled series) is uniform sampling rate.    you are assuming in above that R is uniformly...
It will help me understand the physics of the problem if you describe a bit about the three (y2,y3,y4)time series that you trying to cross-correlate with the y1.  Crosscorrelation...

Re: IFFT Synthesis Amplitude Estimation

Reply posted 5 months ago (08/12/2020)
You do not aim for a specific waveform of the output. Since your requirement is that the amplitude of the sum of the sinusoids not exceed a specific range, say +-A,...
Hello jleman: I posted a reply about 6:30am today (about 9 hours ago), but it seems to have vanished.  So I am retyping it in shorter form.  If dropping a point...
Hello jleman: looks like you have had most of your questions answered.  Since you are in DSP learning mode, perhaps it is useful to restate some basics:1. A sampled...
Since  you obtained B by Fourier Transform of A (since you have computed with sampled data, there is really no difference between 'continuous' FT and FFT),you should...
I agree with CharlieRader.  It is the assignment of the index number.
Since your data is only 64 samples please send the data for A B C and D.  I will take a look with Matlab.cheers
When you state 'FFT/IFFT algorithm adapted for the specific pair', what did you actually do?  I am unfamiliar with Julia, but probably can make some sense of the...
When you go from the frequency domain (A) to the space domain (B) do you examine the imaginary part in the space domain?  The imaginary part should be zero in the...
Notch filters are effectively IIR filters.  They are of a class called 'recursive filters', because the notch filtere uses a part of the output together with the...

Re: Moving Average Filter's Magnitude Response

Reply posted 6 months ago (07/27/2020)
Hello varungupta: Please post a plot of your temperature data, as well as the filtered output.  Since Amplitude and Magnitude are often confusingly used, please...
I thought I will repeat what others have already stated:1. Since you state that you are seeing only the line signal, most likely you have grounding or shielding...

Re: DSPOnlineConference.com - need help testing it.

Reply posted 6 months ago (07/21/2020)
Hello Stephane:I checked out the webpage.  Everything worked smoothly.  Saw no problem.  I registered.  Again, the process was smooth.Thanks for organising...

Re: Sine Dipole formation using two hydrophones

Reply posted 6 months ago (07/20/2020)
Hello naumankalia: Your original question was that you are interested in determining the directivity function of a two element hydrophone array, with opposing phases.In...

Re: Blackman Window FIR Filter Coefficients

Reply posted 6 months ago (07/18/2020)
Hello Gaurav: The figures on p299, CH17, show custom designed filter, and how to obtain the coefficients.  But if your aim is to obtain  a Blackman LPF, then why...

Re: Blackman Window FIR Filter Coefficients

Reply posted 6 months ago (07/18/2020)
Hello Gaurav: I am trying to understand some details. In #1 did you estimate the LPF  frequency response using both +ve and -ve part of the amplitude spectrum? ...

Re: Sine Dipole formation using two hydrophones

Reply posted 6 months ago (07/18/2020)
Hello naumankalia:  You should recognise that you get (near) identical results, whether you derive the dipole field from two oppositely phased closely spaced monopoles,...

Re: Sine Dipole formation using two hydrophones

Reply posted 6 months ago (07/16/2020)
Hello naumankalia: The expression for a monopole is real, but the expression for a dipole  has a multiplying factor (j =sqrt(-1), or, -j).  This arises out of...

Re: Sine Dipole formation using two hydrophones

Reply posted 6 months ago (07/11/2020)
Hellol Naumankalia: I am trying to figure out your problem, and a possible solution if I can. The physics of it should be simple enough.  Please explain what you...

Use this form to contact Platybel

Before you can contact a member of the *Related Sites:

  • You must be logged in (register here)
  • You must confirm you email address