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Adaptive windowing to improve FFT resolution and side lobes rejection

Hi, I come accross a patent found by Russell. The below is the link. http://www.freepatentsonline.com/6298363.html I try to find more information on the Adaptive windowing method but did got any luck. May I know does any one has any opinion or information about the Adapative Windowing method? ...

Inverse windowing

Hi All, I am taking FFT of incoming signal and then windowing (convolving H(f) with the signal) it in frequency domain. After that I perform filtering of the signal. Now before taking the the IFFT, I want to do inverse windowing. What should be my H(f) for this? ...

DFT spectrum and coefficient insight

Hi, I have created a new flash program that gives further insight into the DFT. it is located here. http://www.fourier-series.com/fourierseries2/DFT_tutorial.html I have the new program highlighted on the page. This program explains the DFT coeffiecients and also gives insight into why...

How much do Windowing procedures harm the signal?

Hello experts, I was cruising on Internet for faily long time and I could not get the answer to my questions regarding windowgin procedure. 1. Everybody are writing how good windowing is for supressing leakage (amplitudes at frequencies higher and lower than the signal frequency). Howeve...

How are windowing functions' coefficients extracted?

Hi all, I just wonder why for example Hamming has chosen 'that' special set of coefficient for his windowing function, or any other guy such as Kaiser, Van Haan etc. Is there any mathematical reasoning behind these coefficients or are they just 'discovered' by performing several tests? Vah...

fft and windowing

Hi, I'm doing a spectrum analyzer. i collect 4096 samples of data from codec then I stop interrupt and begin fft. The algoritm that I use ( in the ti's dsplib) does not provide a windowing, so I don't understand if would be ok to do some "by-hand weighted windowing" multiplying a window with the fr...

FFT Windowing and Transmit Pulse Shaping

So I'm pretty confused about something.While studying DFT windowing, I saw how rectangular window has lowest bandwidth compared to Hanning window( which is basically raised cosine), but higher side-lobes. But in all pulse shaping filter tutorials, apart from minimizing ISI they describe how the ban...

How spectral leakage changes the phase spectrum?

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 ...

Re: Phase of FFT compared to phase of Sinusoid

Stan Pawlukiewicz wrote: > robert bristow-johnson wrote: > > Ron N. wrote: > > > robert bristow-johnson wrote: > > > > in article 1143525055.696028.32790@u72g2000cwu.googlegroups.com, Ron N. at > > > > rhnlogic@yahoo.com wrote on 03/28/2006 00:50: > > > > > Within the DFT window, ...

Re: should FFT{x-mean(x)} = FFT{x}-FFT{mean(x)} ?

On 08/28/2010 11:03 AM, thedean515 wrote: > Hi guys, > > The Linearity property of Fourier transform says: > > z(t)=af1(t)+bf2(t) > > the linear combination of the terms is unaffected by the transform. > Z(ω)=aF1(ω)+bF2(ω) > > and > > Z(ω) = FFT{ z(t) }. > ...

Re: Windowing problem before LPC

On Mar 16, 11:08=A0pm, Vladimir Vassilevsky wrote: > hyeewang wrote: > > Why window the signal before computing LPC coefficients? =A0 > > > What is the whys of windowing? =A0I know windowing can prevent spectrum > > leakage,but LPC is none of business of FFT, oh? > > so it ha...

Frequency resolution of FFT after windowing

When I normally do a FFT, the frequency resolution = sampling frequency/number of samples. When I use windowing (like BH4) to prevent smearing, this should increase the frequency resolution of the FFT, because of the convolution in the frequency domain. I have seen tables which show the frequenc...

thx for clay and julius, 'Still mathetical problem, but for AM demodulation with FIR filter"

Clay, thanks for your opinion... my problem is the mathematical equation for how the FIR filter to process demodulation for AM. oya, bout the windowing method, u tell me...i found the equation for bandpass filter ideal. i read a book, and i got the equation for unideal filter. is it h=w.hd? h...

Re: Need help for some simple questions

doggie wrote: ... > 4) What is the purpose of the overlap add method? Why are we doing it? To avoid circular convolution, also called time-domain aliasing. Spectral leakage of the FFT has nothing to do with this. Indeed, if you perform frame windowing and frequency-domain filtering (as in...

Re: short-term energy

"ciskusz" wrote in message news:1gcyc83.a13c3txqo280N%hotaru@alinet.it... > Jerry Avins wrote: > > > Normalizing or not doesn't affect ratios. Why bother? > > Because later I could need the energy for other purpose, hence I have to > window anyway, isn't it? ciskusz, Jerr...

seeking formula for Fourier xform of Hamming family of windowing functions

Can someone please post a closed form *formula* for (not just a plot of) the Fourier transform of windowing functions in the Hamming family of such functions, or at least post link(s) to web page(s) containing such a formula. Thanks in advance, -Michael ...

About windowing question.

Assume a digital signal x,let us call its true spectrum X.then we apply a window w with x,we get y = x.*w. let us call y's true spectrum Y. Then my question is : Are X and Y the same? 1. If they,X and Y, are same, how to account for that they are different in time domain obviously? 2. If t...

Re: The inherent periodicity of the Discrete Fourier Transform

On Feb 8, 10:18=A0pm, robert bristow-johnson wrote: > On Feb 7, 4:31=A0pm, dbd wrote: > ... > first of all, it was Eric who brought up the illustration of the 10.5 > cycle segment of signal that was an example that somehow > differentiated the DFT from the DFS, that this was pro...

Windowed FFT power and amplitude spectrum

Here is another fascinating question on FFT spectrum!! I am trying to find how to incorporate the normalisation factors when windowing is applied to the time series before FFT is applied. When windowing (eg Hanning, flat top etc.) is applied to the time series, the amplitude of the time series...

Re: Blackman Window

Sorry for being late... Already solved it... i've decided not to use windowing. What i'm doing is the following.... As a final university project, i've written a software based on neural networks, able to distortion guitar-digitalized-audio-signals, in offline mode. In order to do so, yo...

FFT windowing and deconvolution

I would like to get some feedback on this idea. Multiplying a signal in the time domain by a window before computing its FFT is equivalent to the convolution of the transform of the signal with the transform of the window. It seems therefore that one could "undo" the effect of a square window (...

Increasing Notch depth using windowing

Hello everyone, Hope no introduction for why I am here (I have a problem.....) Presently i am working on a ofdm simulink implementation where I need to increase the single carrier notch depth (notch is created by putting some carriers to zero)which at present is 13dB(because of 'no window' or ...

DFT output signal power

Hi there, yet another question about DFT/IDFT processing. Here's what I do (assuming 80% overlap): 1) Take let's say 4096 source samples. 2) Perform windowing (using Hann). 3) DFT the result. 4) Here should be some spectral processing, but now it is not. 5) IDFT the result. 6) Perform windowi...

Re: FFT with discontinuities...

Hello, Fourier theory doesn't like discontinuities... it's optimal in a least-squares sense, since it minimizes the integral over the error squared. But that says little about the -peak- amplitude of the error itself. Or, taking an alternative view, the FT result is correct, under the bandwid...

Windowing in the Frequency Domain

Hello there, I'm currently working on a pitch identification program in MATLAB. It uses the Sliding DFT so I need to apply windowing functions in the frequency domain. I understand this is done by convolution and have managed to find the kernel for the von Hann window: [-0.25 0.5 -0.25], but am...

six DFT window functions applied to a 64 point DFT

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 g...

coherent sampling and I/Q demod

(how) does coherent sampling (used primarily in A/D testing?) differ from I/Q demodulation? Say for instance I'm using I/Q to close a PLL. In this case the 'sine wave' I'm locked to is being sampled at x4 the sine frequency. This would seem to satisfy the coherent sampling requirement that regarding...

Re: Equalization using DFT

On Nov 12, 11:26=A0am, "jungledmnc" wrote: > Hi, > > I'm wondering, if there is no problem in equalization with DFT. Simply > window =A0the source signal, DFT, mutliply each frequency bin by a real v= alue > defining it, and IDFT. This would even be zero-phase filtering wouldn't i= t?...

Re: Finding phase and mag at particular freq

Hi, Conceptually: a) Multiply your first stream with the complex sequence exp(-j*2*pi*f*t) The purpose is to downconvert your "f" of interest to 0 Hz b) Do the same for the other stream c) low-pass filter both results. This is the tricky part, unless your signal is cyclic - for example one ...

Peak Windowing for OFDM

Hi I am trying to implement a program in Matlab in order to apply a window to the peaks of the envelope of an OFDM signal. The window I am using is a Gaussian window, with factor gamma (exp(-gamma*t^2)) I have already implemented it, but I do not know if the results obtained are so satisfactor...

Re: Autocorrelation

> My question was for a more general case... A lot of people says that > the autocorrelation is dominated by a cardinal sinus (ie something > like sin(A)/A), Which people say that and under what context?? Once again, the autocoreleation description that you mentioned above is what I would...

Re: Removing a window function (any ideas?)

The window function can be applied by a vector multiply in the time domain or a small convolution in the frequency domain. The frequency domain version can be represented as a vector-matrix multiply. If the frequency domain windowing matrix is invertible, the inverse matrix can be used to remove...

Re: Unusual Impulse Resp. from Parks-McClellan

"Jerry Avins" wrote in message news:bklsqc$j53$1@bob.news.rcn.net... I learned here recently that other optimizations -- least square error, for example -- often yield more desirable impulse responses. With a few extra taps and a nice window like Blackman, the problem doesn't arise. Does t...

Re: formula for hanning (sic) filter

Perhaps it really should be called the "von Hann" window? Does it really matter? We could call it the "cosine-squared" window, as I believe some physicists like to do, and cut Herr von Hann out completely. "Can't we all just get along?" - Rodney King Note that the relationsh...

How to compute phase of FFT signal in real world?

Hi, I am trying to compute the amplitude and phase of signal with specific frequency. The frequency of the signal is known (measured with laser - the rotation machine). I tried to simulate the computation in matlab first: close all clear all % clc f = 50; % Frequency of si...

Re: SNR calculation using FFT

Cheng, The SNR calculation using FFT method does not depend on the number of points (assuming it to be large to begin with). Couple of things that needs to be considered while computing FSNR (I call it Frequency domain SNR Calc, time domain would be called TSNR). 1...

Re: A little question about THD+N

It can be done without windowing, as Randy said. It can also be done with windowing, but why make it more complicated. I've got an example on my web page, that does a similar job. If you like, have a look (below). The method is a bit more complicated, but you could copy the general approach: -...

FIR notch filters using the Windowing method

Hi, I am trying to obtain a FIR notch filter which is very narrow. For example, a 50 Hz notch filter to remove mains noise from a 1250Hz signal say. Doing this with an IIR filter was easy, I could specify my "notch region" as small as [49 51]Hz. I am now trying to do the same with a FIR fi...

Re: PitchShift using STFT

How are the clicks suppresed? Is it because of the windowing being done? I am still not able to correlate the two? Help. Regards --Himanshu ...

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

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 str...