Why (if) should be windows in spectral analysis nonnegative ?

Started by Robert Rozman in comp.dsp16 years ago 18 replies

Hello, I'm reading a lot of literature on windowing in spectral analysis but haven't found theoretical cause of background for statement that...

Hello, I'm reading a lot of literature on windowing in spectral analysis but haven't found theoretical cause of background for statement that windows sequences should be nonnegative. It seems logical that weighting should be done with positive factors but since gained frequency response is convolution integral between "real" response and window's response there seems to be no cause for no...


Name of this window

Started by Anonymous in comp.dsp15 years ago 15 replies

I've started using a simple windowing function to low pass filter a 2D image. Following the FFT, I multiply in the frequency domain with...

I've started using a simple windowing function to low pass filter a 2D image. Following the FFT, I multiply in the frequency domain with a function that increases with distance from the origin (allowing for wrapping). Then I IFFT back to the image domain. Basically the window is this: f = sqrt(alpha / (alpha + x^2 + y^2)) where x,y range from 1-n/2 to n/2 and alpha is a scalar. Anyone k...


Spectrogram Plot to Bitmap Output

Started by BobM in comp.dsp13 years ago 2 replies

Hi Everyone, I'm looking to make a small C/C++ command-line utility which takes a binary audio file as input and generates a spectrogram of a...

Hi Everyone, I'm looking to make a small C/C++ command-line utility which takes a binary audio file as input and generates a spectrogram of a given time range of the file. First off, I am already comfortable with reading/writing binary audio files, as well as the "back end" requirements for generating spectrogram information (FFT, windowing, etc.). What I am not familiar with is gener...


Questions about "windowing & bin width" and "DCT/DST & convolution"

Started by Richard Owlett in comp.dsp9 years ago 6 replies

CAVEAT - My formal coursework in "Signals and Systems" predates undergrads being introduced to Cooley, Tukey etc. I'm also such an antique...

CAVEAT - My formal coursework in "Signals and Systems" predates undergrads being introduced to Cooley, Tukey etc. I'm also such an antique that I visualize in terms of RLC tank circuits characterized by Q ~= F0/BW. (My father operated a legal land based spark gap transmitter and built his own capacitors in a fish tank obtaining ~ 1 ufd/gal {no idea what the insulation was} ;) BACKGROU...


FIR filter design question

Started by Zeph80 in comp.dsp11 years ago 7 replies

In windowing method for FIR design, you specify the frequency response of the desired filter at sample points fs/N, and perform an IDFT to...

In windowing method for FIR design, you specify the frequency response of the desired filter at sample points fs/N, and perform an IDFT to obtain h(n). So doesnt this mean that you want fs to be as low as possible to specify better frequency resolution. But Fs is generally many times the cut-off frequency - more than the minimum of twice the cut off needed. Why is this?Isn't the frequency res...


Audio output distorted with any FFT windowing other than rectangular

Started by tomb18 in comp.dsp5 years ago 18 replies

Hi, For an experiment i have a simple application that takes a quadrature signal from a radio and then does the following: Complex FFT -> ...

Hi, For an experiment i have a simple application that takes a quadrature signal from a radio and then does the following: Complex FFT -> Inverse FFT -> Cartesian to Polar -> audio out If I tune the radio to an AM signal I can demodulate it perfectly well by this but it depends on how the FFT is processed. In the FFT routine, I apply a window and if it is anything other than a rectangular wind


Phase is affected by windowing?

Started by Salvadorr in comp.dsp13 years ago 3 replies

Hello for everybody!!!!!!!!!!!!! I write a program for FHT(Hartley) and i wtite a flat top, hanning and hamming window function everything is...

Hello for everybody!!!!!!!!!!!!! I write a program for FHT(Hartley) and i wtite a flat top, hanning and hamming window function everything is ok here. Im analysing 2 signal of 60 Hz both. v=sin(2pif) i=sin(2pif-theta_i) theta=theta_v-theta_i if theta_i is between 0-27 degrees and theta_v=0 there?s no problem theta= angle between 0-27 but if theta_i is for example 28 or more (theta_v = ...


Denoising and envelop detection

Started by wolverine_w2000 in comp.dsp11 years ago 2 replies

Hi, I am working on radar processing and I am new to this study. I have 1D time domain data and I used windowing technique and 'fft'ed the data...

Hi, I am working on radar processing and I am new to this study. I have 1D time domain data and I used windowing technique and 'fft'ed the data and plotted the data using imagesc and it is a spectrogram. My question is to denoise the spectrogram and to extract the data from the envelope obtained in the spectrogram. I am working this study in Matlab. Can any one suggest me denoising algorithm and e...


Illustrating concepts of FFT bin width and spectral leakage

Started by Richard Owlett in comp.dsp10 years ago

Recent discussion of bin width got me thinking about that and the how/why of windowing data before performing an FFT. As one who always did...

Recent discussion of bin width got me thinking about that and the how/why of windowing data before performing an FFT. As one who always did better in lab courses than theory, I decided to do some experiments. The attached program is my attempt to illustrate effects of window width and sampling frequency. I plan to add illustrations of effect of window type and numerical precision (emu...


MFCC

Started by nerdlinger in comp.dsp9 years ago 2 replies

Hi all, long time reader, first time posting as a member. My query relates to MFCC calculation. Generally speaking I have an ok verbal...

Hi all, long time reader, first time posting as a member. My query relates to MFCC calculation. Generally speaking I have an ok verbal understanding of MFCC's, however I never had a detailed understanding. Firstly, im trying to implement this in MATLAB (this being MFCC calculation). Im fairly all right at MATLAB, so the previous steps to MFCC calculation such as windowing and framing a...


Wiener adaptive filtering and windowing: discontinui

Started by sandro in comp.dsp14 years ago 1 reply

Hi all, I wrote a simple adaptive wiener filter in matlab to remove noise from an audio file. The routine computes correlation matrixes on a...

Hi all, I wrote a simple adaptive wiener filter in matlab to remove noise from an audio file. The routine computes correlation matrixes on a rectangular window of 256 samples but I have difficulties when rebuilding the whole file: on every edge of the filtered windows I have a discontinuities, so the global result is corrupted. http://img208.imageshack.us/img208/950/wiener4kq.jpg Cou...


Windowing

Started by Anonymous in comp.dsp13 years ago 10 replies

Hello, I'm new to dsp, still much to learn. I'm working on something that will apply window function to signal read from a .wav file. Until...

Hello, I'm new to dsp, still much to learn. I'm working on something that will apply window function to signal read from a .wav file. Until now I've developed a code that reads the data and loads it into memory buffer. The code looks like: "int main(int argc, char *argv[]) { FILE *fwyj,*fout; double ts,tk,time; float f0,pr,window; int z,N; long start_byte,end_byte; long new_d...


Spectral analysis

Started by Tom in comp.dsp13 years ago 13 replies

Hi, I am familiar with computing the spectrum of a real time signal using FFT after windowing it using a window such as hamming to increase...

Hi, I am familiar with computing the spectrum of a real time signal using FFT after windowing it using a window such as hamming to increase the resolution of the spectrum, however I need to compute the spectrum of a complex signal, can anybody explain how to window a complex signal before computing the FFT. Thanks Tom


Hanning window - I/Q signal

Started by r.a.m- in comp.dsp4 years ago 1 reply

Hi everybody, I have implemented Hann windowing function as follows: var N = samples.Length / 2; for (int i = 0; i < samples.Length;...

Hi everybody, I have implemented Hann windowing function as follows: var N = samples.Length / 2; for (int i = 0; i < samples.Length; i++) { samples[i] *= 0.5 - 0.5 * Math.Cos((2 * Math.PI * i) / (N - 1)); } Samples field consists of varying real and imaginary values. When i apply Hann window my signal mirrors every time at negative frequency, ergo the peak shoul


autocorrelation for frequency estimation question

Started by Anonymous in comp.dsp16 years ago 5 replies

When using an fft for frequency estimation of a complex audio waveform (singing voice, piano, etc.), the bin representing half the...

When using an fft for frequency estimation of a complex audio waveform (singing voice, piano, etc.), the bin representing half the fundamental frequency will be mostly empty. Won't the bin of the autocorrelation result for double the wavelength of the fundamental frequency have some energy in it? How does one handle this false positive? Also, the fft of short segments requires windowing f...


Usage of windowing for FFT order analysis

Started by MedievalMan in comp.dsp11 years ago 6 replies

Hi; I have an algorithm in VBA that: -takes the sampled (500-1000 Hz) Torque signal, and splits it up into sections that correspond to each...

Hi; I have an algorithm in VBA that: -takes the sampled (500-1000 Hz) Torque signal, and splits it up into sections that correspond to each revolution of the machine. - For each revolution of torque data, I interpolate the data to fit a power of 2 samples for the FFT algorithm. - I take the FFT of each revolution of torque data, and then chop all but the 1st 4 orders of the spectrum. ...


Regarding Linear prediction analysis.

Started by neelufar.2005 in comp.dsp12 years ago 3 replies

Hi, I am working on the linear prediction analysis implementation,I have one question which is regrding windowing which is done before LCP,...

Hi, I am working on the linear prediction analysis implementation,I have one question which is regrding windowing which is done before LCP, where we have a frame of size 240 samples i.e 40 samples from past, 80 samples of present frame and 40 samples from future. I am using the linear prediction analysis for decorrelation of signal after acoustic echo cancellation. I can store the 40 sample...


windowing question

Started by Anonymous in comp.dsp14 years ago 23 replies

Suppose that I have a continous-time signal that consists of a finite number of Dirac impulses at integer time points. For example, lets say the...

Suppose that I have a continous-time signal that consists of a finite number of Dirac impulses at integer time points. For example, lets say the signal starts at t=0 and lasts for 100 seconds, with 100 dirac impulses, one per second. It's easy to take the Fourier Transform of this signal, since it is time-limited. Now lets apply a rectangular window to this signal, such that only 50 sec...


Overlap-Add Question

Started by stau...@gmail.com in comp.dsp14 years ago 15 replies

Hi, I have a question about the overlap-add technique. I am taking some raw audio data and I'm windowing it with 4096 point FFTs (and throwing...

Hi, I have a question about the overlap-add technique. I am taking some raw audio data and I'm windowing it with 4096 point FFTs (and throwing away the data that is reflected so I get 2047 points for each window). The windows are non-overlapping. In the frequency domain, I set some frequency bins to zero and then I do an IFFT with each window (making sure to put back the reflected data) wh...


MATLAB Hamming Window-Applying Multiple Windows to one Signal

Started by kachi in comp.dsp11 years ago 2 replies

I have a question about windowing in MATLAB. So I have a 1 second signal, y1 to which I would like to apply a 24ms hamming window. Within...

I have a question about windowing in MATLAB. So I have a 1 second signal, y1 to which I would like to apply a 24ms hamming window. Within the windowed signal, I want to perform a series of calculations . From what I understand about windows you can simply multiply y1 and the window function to get the windowed signal. I'm curious though is it possible to split that 1 sec signal into many (approx...