CODEWITHSUNDEEP
c++matlabsignal-processing
Jordan
Jordan

Reputation: 4502

Matlab Hilbert Transform in C++

First, please excuse my ignorance in this field, I'm a programmer by trade but have been stuck in a situation a little beyond my expertise (in math and signals processing).

I have a Matlab script that I need to port to a C++ program (without compiling the matlab code into a DLL). It uses the hilbert() function with one argument. I'm trying to find a way to implement the same thing in C++ (i.e. have a function that also takes only one argument, and returns the same values).

I have read up on ways of using FFT and IFFT to build it, but can't seem to get anything as simple as the Matlab version. The main thing is that I need it to work on a 128*2000 matrix, and nothing I've found in my search has showed me how to do that.

I would be OK with either a complex value returned, or just the absolute value. The simpler it is to integrate into the code, the better.

Thank you.

Upvotes: 4

Views: 15628

Answers (4)

André Bergner
André Bergner

Reputation: 1439

The MatLab function hilbert() does actually not compute the Hilbert transform directly but instead it computes the analytical signal, which is the thing one needs in most cases. It does it by taking the FFT, deleting the negative frequencies (setting the upper half of the array to zero) and applying the inverse FFT. It would be straight forward in C/C++ (three lines of code) if you've got a decent FFT implementation.

Upvotes: 9

Johannes Rebling
Johannes Rebling

Reputation: 11

Not a true answer to your question but maybe a way of making you sleep better. I believe that you won't be able to be much faster than Matlab in the particular case of what is basically ffts on a matrix. That is where Matlab excels!

Matlab FFTs are computed using FFTW, the de-facto fastest FFT algorithm written in C which seem to be also parallelized by Matlab. On top of that, quoting from http://www.mathworks.com/help/matlab/ref/fftw.html:

For FFT dimensions that are powers of 2, between 214 and 222, MATLAB software uses special preloaded information in its internal database to optimize the FFT computation.

So don't feel bad if your code is slightly slower...

Upvotes: 0

user3085701
user3085701

Reputation: 1

Simple code below. (Note: this was part of a bigger project). The value for L is based on the your determination of your order, N. With N = 2L-1. Round N to an odd number. xbar below is based on the signal you define as the input to your designed system. This was implemented in MATLAB.

L = 40;
n = -L:L; % index n from [-40,-39,....,-1,0,1,...,39,40];
h = (1 - (-1).^n)./(pi*n); %impulse response of Hilbert Transform
h(41) = 0; %Corresponds to the 0/0 term (for 41st term, 0, in n vector above)

xhat = conv(h,xbar); %resultant from Hilbert Transform H(w);

plot(abs(xhat))

Upvotes: 0

Matt Phillips
Matt Phillips

Reputation: 9691

This looks pretty good, as long as you can deal with the GPL license. Part of a much larger numerical computing resource.

Upvotes: 2

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