## How Shifting and Scaling in Continous signals is related to Images

Started by in comp.dsp11 years ago 2 replies

Hello Everybody! I am doing a study of wavelets. I am able to get basic idea of wavelets as how the input signal is multiplied with a scaled...

Hello Everybody! I am doing a study of wavelets. I am able to get basic idea of wavelets as how the input signal is multiplied with a scaled and shifted windowing function.But I am not clear of how the filtering process is carried out for 2-d matrices or images. Can anybody tell me how shifting and scaling of wavelets in continous time signals is related to images. Thanks in advance! Narin...

## Sharpening oversampled STFT-based spectrograms

Started by in comp.dsp11 years ago 17 replies

If you made a spectrogram by windowing in the time domain using an infinitely long window (let's go for a Gaussian function) every one sample in...

If you made a spectrogram by windowing in the time domain using an infinitely long window (let's go for a Gaussian function) every one sample in the signal (that is centre your window on each sample and DFT each time), you would obtain a huge and very blurry spectrogram. But this huge blurry image wouldn't be aliased, so the thought occurred to me, since it's oversampled and not aliased, and ...

## DSP Spectral Analysis using MATLAB

Started by in comp.dsp13 years ago 1 reply

Hi everyone, I am new with matlab and am having problems with a spectral analysis problem i'm trying to do. I need to perform spectral analysis...

Hi everyone, I am new with matlab and am having problems with a spectral analysis problem i'm trying to do. I need to perform spectral analysis of a signal consisting of 1000Hz, 1000.1Hz and 999.9Hz i.e., x=cos(2*pi*1000*t)+cos(2*pi*1000.1*t)+cos(2*pi*999.9*t) so that all the three peaks are seen. This is to be done using a windowing function like blackmann-harris/guassian. I wrote the m-...

## How spectral leakage changes the phase spectrum?

Started by in comp.dsp12 years ago 9 replies

Hello All, I want to understand how spectral leakage changes the phase spectrum of a sine wave? Also when I apply window...

Hello All, I want to understand how spectral leakage changes the phase spectrum of a sine wave? Also when I apply window (blackman harris 11 Term or chebyshev window with 300db attenuation), I see a significant amount of reduction in spectral leakage in the amplitude part of the spectrum. But this windowing also affects the phase part of the ...

## Spectral Analysis using MATLAB

Started by in comp.dsp13 years ago 4 replies

Hi everyone, I am new with matlab and am having problems with a spectral analysis problem i'm trying to do. I need to perform spectral analysis...

Hi everyone, I am new with matlab and am having problems with a spectral analysis problem i'm trying to do. I need to perform spectral analysis of a signal consisting of 1000Hz, 1000.1Hz and 999.9Hz i.e., x=cos(2*pi*1000*t)+cos(2*pi*1000.1*t)+cos(2*pi*999.9*t) so that all the three peaks are seen. This is to be done using a windowing function like blackmann-harris/guassian. I wrote the m-...

## Might "spectral leakage" be irrelevant?

Started by in comp.dsp16 years ago 2 replies

In another thread Rick Lyons said: "Windowing is generally used to reduce the spectral leakage that causes a strong (high amplitude) signal's...

In another thread Rick Lyons said: "Windowing is generally used to reduce the spectral leakage that causes a strong (high amplitude) signal's spectral magnitude to cover over (swamp out) the spectral components of nearby weak signals. If a weak signal (in which you're interested) is 3-4 FFT frequency bins away from a strong signal's center frequency, use the Hamming window. If the weak s...

## FFTW Accuracy vs Matlab Accuracy

Started by in comp.dsp13 years ago 12 replies

Hi, i'm using FFTW to computer determine the SNR of a recorded sinusoidal signal. (1khz sinus for 5seconds @ 48khz) I'm experiencing a...

Hi, i'm using FFTW to computer determine the SNR of a recorded sinusoidal signal. (1khz sinus for 5seconds @ 48khz) I'm experiencing a strange behaviour: if i compute the fft with FFTW i obtain really different values from what matlab compute. To be more specific: i compute a real 2 real fft with: ApplyWindow(BLACKMANHARRIS);//

## six DFT window functions applied to a 64 point DFT

Started by in comp.dsp12 years ago 2 replies

Hi, I have created a new flash program that shows how windowing is used to reduce leakage in a DFT. The program also discussed magnitude...

Hi, I have created a new flash program that shows how windowing is used to reduce leakage in a DFT. The program also discussed magnitude and power representation of the DFT coefficients. The program allows you to run a 64 point DFT. The DFT allows two frequency inputs with variable gain on the input levels of each frequency. You can apply six window functions and vary the signal...

## Zero padding and the Shannon information content

Started by in comp.dsp13 years ago 10 replies

Hello all, I am confused about how zero-filling / windowing a signal alters its information content and I'm hoping someone here can help. I...

Hello all, I am confused about how zero-filling / windowing a signal alters its information content and I'm hoping someone here can help. I have a continuous signal (time domain) and I Fourier transform it to get a band-limited spectrum (frequency domain). From Shannon & Weaver, I can compute the information content of the time domain signal from the signal variance and, given the linea...

## FFT magnitude for frequency analyzer

Started by in comp.dsp11 years ago 4 replies

Hi there, I'm trying to implement frequency analyzer for audio signal using DFT. Nothing extraordinary, just take e.g. 4096 source samples, apply...

Hi there, I'm trying to implement frequency analyzer for audio signal using DFT. Nothing extraordinary, just take e.g. 4096 source samples, apply windowing, pass through DFT and get magnitude of particular frequency bin via msqrt(msqr(Re) + msqr(Im)) , then maybe some overlapping or whatsoever. Let's say, that source samples are in -1..1. The problem is, even if the source signal is for e...

## MATLAB code for Power Spectral Density

Started by in comp.dsp14 years ago 11 replies

Can anyone please check if my code is correct? SINE512 is just a file name. This file has 512 data points and it's a sine wave. Thank...

Can anyone please check if my code is correct? SINE512 is just a file name. This file has 512 data points and it's a sine wave. Thank you!! %Sampling frequency Fs=50000; %# of samples in the data datasize=size(SINE512); numsample=datasize(1); %Windowing H=hann(numsample); W=H.*(SINE512(:,2)); %Fourier Transform FFTX=fft(W,numsample); %Power: magnitude^2 X=FFTX(1:floor(numsamp...

## Windowing question

Started by in comp.dsp16 years ago 2 replies

Hi, I noticed this phenomena when using a Hanning window before using FFT of 4096 size. If the data that I put into the FFT is up to about 2048...

Hi, I noticed this phenomena when using a Hanning window before using FFT of 4096 size. If the data that I put into the FFT is up to about 2048 samples, Hanning window reduces the side-lobes as expected. But if I use more data on the FFT such as 4096 samples, the Hanning window actualy add more side-lobes than Rectangular. Is this the way it supposed to work? I used Sound-Forge spectrum anal...

## equivalent operations in the time-domain & the frequency-domain

Started by in comp.dsp15 years ago 4 replies

Hi all, You know how convolution in the time-domain is the equivalent of multiplication in the frequency-domain, and vice-versa.... can...

Hi all, You know how convolution in the time-domain is the equivalent of multiplication in the frequency-domain, and vice-versa.... can anyone explain to me what would be the frequency-domain equivalent of taking an "inner-product" in the time-domain?? For a signal-detection problem I've had some success with a matched filter, windowing through data and taking time-domain inner-product...

## FFT with TMS320F2812

Started by in comp.dsp11 years ago 3 replies

I use the TI FFT Library and I have two question : First, in the TI example RFFT32_brev(ipcb,ipcb,N); RFFT32_brev(ipcb,ipcb,N);// Input...

I use the TI FFT Library and I have two question : First, in the TI example RFFT32_brev(ipcb,ipcb,N); RFFT32_brev(ipcb,ipcb,N);// Input samples in Real Part fft.win(&fft); RFFT32_brev(ipcb,ipcb,N); RFFT32_brev(ipcb,ipcb,N);// Input after windowing fft.calc(&fft); fft.split(&fft); fft.mag(&fft); There are 4 times "RFFT32_brev(ipcb,ipcb,N); ", I don't know why ? I deleted the last 3 l...

## use matlab to do short time fourier transform

Started by in comp.dsp16 years ago 4 replies

Hi all the experts, I would like to use Matlab to do short time fourier transform on a speech signal. May I know how can I use the windowing...

Hi all the experts, I would like to use Matlab to do short time fourier transform on a speech signal. May I know how can I use the windowing function and fft function to do the short time fourier transform? (I know there is a blockset to do that but I'm not allowed to use simlink to do the short time fourier transform. So please help! Thank alot. David

## window and fft

Started by in comp.dsp16 years ago 10 replies

Hi, I have a little problem ... I am working with audio datas, I get the datas block by block. I have to process the datas in the fourier...

Hi, I have a little problem ... I am working with audio datas, I get the datas block by block. I have to process the datas in the fourier domain, for that I windowing a signal block and then I compute the fft, process the block in the fourier domain, compute the ifft and overlap with a previous processed block. The problem is that the processing in the fourier domain modify the signal phas...

## 2D FFT window function

Started by in comp.dsp11 years ago 3 replies

I have some questions about length of windowing functions applied to 1D and 2D FFT. For a N point 1D FFT, it is very straightforward, I can...

I have some questions about length of windowing functions applied to 1D and 2D FFT. For a N point 1D FFT, it is very straightforward, I can generate a N point window function, and multiply it with the signal before doing FFT. But for N*N point 2D FFT, what length of window function should I use? Should I generate a N*N point window same to the one used in 1D FFT, or a N point window and repeat the...

## Positive functions in both their time and frequency representations? (i.e. Gaussian function)

Started by in comp.dsp11 years ago 18 replies

Are there any (windowing) functions out there that are positive in the time domain as well as in the frequency domain? I know the...

Are there any (windowing) functions out there that are positive in the time domain as well as in the frequency domain? I know the Gaussian function is strictly positive in both, the Fourier transform of a Gaussian function being a Gaussian function. But are there any other functions that are stricly positive in both the time and frequency domain? The reason I'm asking this is that I'm look...