I am trying to approximate shape boundaries by using Fourier descriptors. I know this can be done because I've learned about it in class and read about it in several sources. To obtain the Fourier descriptors of a boundary of (x,y) coordinates, I do the following: 1) Turn (x,y) coordinates into complex numbers of the form x + iy 2) Feed...
On my 64-bit Debian/Lenny system (4GByte RAM + 4GByte swap partition) I can successfully do: v=array(10000*random([512,512,512]),dtype=np.int16) f=fftn(v) but with f being a np.complex128 the memory consumption is shocking, and I can't do much more with the result (e.g modulate the coefficients and then f=ifftn(f) ) without a MemoryEr...
Hello, I have a small query regarding the discrete Fourier transforms. If I understand correctly, then what we do is convert a polynomial to its point value representation, with n points for a polynomial that goes up to the power of n-1. But why must we evaluate it at the nth roots of unity? Wouldn't any other n points uniquely identify ...
Say i'm trying to evaluate the Polynomial: x^2 + 1 Using the Fast Fourier transform method for evaluating co-efficients. Now i can change this into matrix/vector form using the co-effcient as inputs for the fast fourier transform: so: x^2 + 1 = <1, 0, 1, 0> This is done by using the coefficient value e.g 1 = 1, 0x^1 = 0, X^2 = 1 a...
Hi, I'm trying to process audio data. I'm working with Java. I've extracted the audio data to an array. Now I should pass N data samples to a function that calculates the Discrete Fourier Transform (or Fast Fourier Transform, which is more efficient). I've read documentation but I'm getting more and more confused. What I'm trying to cal...
Hello. I'm trying to convert an image into an audio signal in MATLAB by treating it as a spectrogram as in Aphex Twin's song on Windowlicker. Unfortunately, I'm having trouble getting a result. Here it what I have at the moment: function signal = imagetosignal(path, format) % Read in the image and make it symmetric. image = ...
Taking speed as an issue it may be better to choose another language, but, what is your library/module/implementation of choice for doing 1D FFT in python? ...
I want to take audio PCM data and find peaks in it. Specifically, I want to return the frequency and time at which a peak occurs. My understanding of this is that I have to take the PCM data and dump it into an array, setting it as the real values with the complex parts set to 0. I then take the FFT, and I get an array back. If each ...
from Wikipedia: fourier division. Here is a screenshot of the same: (view in full-resolution) What is the logic behind this algorithm? I know it can be used to divide very large numbers, but how exactly does it work? ...
With a sine input, I tried to modify it's frequency cutting some lower frequencies in the spectrum, shifting the main frequency towards zero. As the signal is not fftshifted I tried to do that by eliminating some samples at the begin and at the end of the fft vector: interval = 1; samplingFrequency = 44100; signalFrequency = 440; sample...
Hello, I've done a fft to get fundamental frequency in real time and to implement high and low pass filters. Now I want to be able to record to a .wav file after I apply a filter. First I'll have to invert the fft and that is my question. What are the steps to do this? I use the FFT defined in this project. Here is the code for it: ...
Hello, I used made a fft to make a band pass filter. After that I made the ifft to inverse it and pass it to time domain. My ifft has the same length of the fft. The ifft must be longer or is there a way to make it longer? How do I pass this ifft to .wav? ...
Hello, is there a free c# library to do the fast fourier transform and its inverse? ...
If we get the sound from microphone with two channels, to calculate the frequency spectrum we: calculate the fast fourier transform of all the data input? calculate the fast fourier transform of each left and right channel and then make a average of both? calculate the fast fourier transform of each left and right channel and get the b...
The Fast Fourier Transform takes O(N log N) operations, while the Fast Wavelet Transform takes O(N). But what, specifically, does the FWT compute? Although they are often compared, it seems like the FFT and FWT are apples and oranges. As I understand it, a more appropriate comparison would be the STFT (FFTs of small chunks over time) ...
Hey, I have performed an fft (fast fourier transform) on a time series waveform in Matlab, but I seem to have a weird wave actually in the fourier transform plot, although there are spikes this wave looks like something I'd expect to see only in the time domain. Is there any programming reason why this could happen? ...
I am trying to compare two data sets in MATLAB. To do this I need to filter the data sets by Fourier transforming the data, filtering it and then inverse Fourier transforming it. When I inverse Fourier transform the data however I get a spike at either end of the red data set (picture shows the first spike), it should be close to zero a...
I know that if we have some data representing some wave, for example image line values, we can use fourier transform to get frequency function of that wave. But we have N values at points x=0...N-1 And we get only N frequencies at the output. So I want to analyze the wave everywhere in the range [0, N-1] For example at point u = 1.5. ...
Is there a way to compute efficiently the Fourier transform of the max of two functions (f,g), knowing their Fourier transform? ...
As we know Fourier Transform is sensitive to noises(like salt and peppers), how can it still be used for image recognization? Is there a FT expert here? ...