## cross correlation

Started by in comp.dsp16 years ago 1 reply

Hello Everybody, i am a newcomer to dsp as well as this usenet. i was studying cross correlation using matlab, the two signals which i used...

Hello Everybody, i am a newcomer to dsp as well as this usenet. i was studying cross correlation using matlab, the two signals which i used were a 1 hz sine and a 2 hz sine, the waves were sampled at 10hz, i got 2 correlation peaks one at 8th bin and other at 14th , why there are two peaks?, is it that if we get more than one peak, the correlation result cannot be accepted as the above two si...

## Cross-correlation by convolution (unexpected results)

Started by in comp.dsp16 years ago 22 replies

Since an image is word ten thousand words, here's what sums up what i'm trying to do http://www.geocities.com/michel0528/correlation.jpg As...

Since an image is word ten thousand words, here's what sums up what i'm trying to do http://www.geocities.com/michel0528/correlation.jpg As you can see, I'm trying to correlate the first signal by the second by correlation. The problem is, I didn't really expect the result you can see on the picture, I expected more something looking like from not too close like a delta function right in th...

## Cross Correlation & Accuracy

Started by in comp.dsp16 years ago 4 replies

i've implemented a cross correlation algorithm for an audio software, but the values i find aren't accurate enough for the use i need. For...

i've implemented a cross correlation algorithm for an audio software, but the values i find aren't accurate enough for the use i need. For example, using -exactly- the same signal delayed by 1024 samples (at 44100 Hz samplerate) i find results between 985 and 1020, never 1024, and sometimes totally wrong values. I used buffers of 262144 samples (6 sec) to 1048576 samples (24 sec), which seems...

## What is happening with the Cross-Correlation and Power Spectra of these signals?

Started by in comp.dsp16 years ago 8 replies

Hi all, I am trying to extract some caracteristic velocity from two time signals obtained from two sources apart from a distance DX. In order...

Hi all, I am trying to extract some caracteristic velocity from two time signals obtained from two sources apart from a distance DX. In order to get the velocity I am dividing the distance DX by the maximum time lag of the cross-correlation. However I am getting the maximum time lag to be at t = 0. Does anybody have a clue about what is happening ? My other doubt is when I try to get the ...

## Normalization and cross-correlation - what am I doing wrong?

Started by in comp.dsp16 years ago 3 replies

Hi NG, I have a problem regarding normalization when performing cross-correlation: I have a relatively short signal/waveform ("A") which...

Hi NG, I have a problem regarding normalization when performing cross-correlation: I have a relatively short signal/waveform ("A") which I'm cross-correlating with a longer timeseries ("B") to look for this waveform. Since there are large fluctuations in B, I have decided to apply some sort of normalization scheme to both A and B. So, for A I divided all the samples with the squareroot ...

## Cross Correlation - phase or magnitude or both?

Started by in comp.dsp15 years ago 3 replies

I have written a cross correlation algorithm which is giving me quite a few problems. From what is looks like, and from the descriptions of...

I have written a cross correlation algorithm which is giving me quite a few problems. From what is looks like, and from the descriptions of cross correlation on this site are telling me, i think i found the problem...however I cant think of how to fix it. Hopefully you can help. Here is the situation which has been described in more details in other threads. I have a template of data, of len...

## cross correlation implemenation

Started by in comp.dsp15 years ago 1 reply

For starters, I hope I'm not off topic. I'm looking for a C/C++ cross correlation implemention. Something akin to matlab xcorr. I'm...

For starters, I hope I'm not off topic. I'm looking for a C/C++ cross correlation implemention. Something akin to matlab xcorr. I'm perusing the matlab source for xcorr and - it's so say the least - intimidating. Trying to convert my matlab source to C++ but would hate to re-invent the wheel if a sound implementation of these exists someplace. Thanks in advance

## I need 2D cross correlation code

Started by in comp.dsp15 years ago 2 replies

Hello all, for the last month i was searching for 2D cross correlation code in C/C++ with no success. I also tried many times to use the...

Hello all, for the last month i was searching for 2D cross correlation code in C/C++ with no success. I also tried many times to use the 'mcc' function in matlab & convert the normxcorr2.m into C/C++ but it's issuing so many problems I'll spare you with. Can you direct me to a good source or advise me with a solution? Thanks in advance.

## Cross correlation

Started by in comp.dsp15 years ago 2 replies

Hello, I have a problem with my C code. My algorithm might be wrong but when I work with fewer samples, I get convinced that I am right. In...

Hello, I have a problem with my C code. My algorithm might be wrong but when I work with fewer samples, I get convinced that I am right. In C I have two arrays: Data and Code. They are both array of structs (both are array of imaginary numbers). Now, according to my shorter calculations, if I keep Data constant and shift only Code array or vice versa, I ought to end up with the cross correl...

## Cross correlation and system ID

Started by in comp.dsp15 years ago 2 replies

I was looking at this link http://www.prosig.com/signal-processing/CorrelationExample.html and is says that for a system with excitation x...

I was looking at this link http://www.prosig.com/signal-processing/CorrelationExample.html and is says that for a system with excitation x and output y that the transfer function is found to be H(f)=Gxy(f)/Gxx(f) where Gxy is cross power spectrum and Gxx is auto power spectrum. Trouble is - H(f) must be uncausal (or unstable) since Power spectrum has poles in the right half plan...

## Using cross-correlation function to recognize signal pattern

Started by in comp.dsp15 years ago

Hi. I have cetain sampled sequence out of non-stationary audio signal featured by certain noise pattern (which is also non-stationary in details...

Hi. I have cetain sampled sequence out of non-stationary audio signal featured by certain noise pattern (which is also non-stationary in details but is well defined in general). I intend to run numerous recordings featuring this noise, to separate the noise pieces ad process them in order to obtain some kind of averaged noise stamp (in time domain) and then to use it by cross-correlation with an ...

## Reverse a cross correlation with MatLab

Started by in comp.dsp15 years ago 3 replies

I have a cross-correlation signal and one of the two signas that were cross-correlated: CC=A*B I have CC and let's say A. Now I try to find the...

I have a cross-correlation signal and one of the two signas that were cross-correlated: CC=A*B I have CC and let's say A. Now I try to find the second signal B. In detail: CC and A is are normalized envelops of a pulse that are kind of gaussian. At the beginning and the end of the vektors there are a lot of zero values. I played around with the original formulars with FFT, but doing the d...

## How to design a DFE equalizer?

Started by in comp.dsp15 years ago

Hi, I want to know how to design a DFE equalizer. In some text books, it gives the formular but I don't know how to calculate the...

Hi, I want to know how to design a DFE equalizer. In some text books, it gives the formular but I don't know how to calculate the correlation and cross correlation matrix. On the other hand, some material gives formular when one have the received training samples. My situation is that I know the channel impulse response (of course, this is a assumption). How to design a DFE with the criterio...

## Extracting waveform from WAV files using libsndfile

Started by in comp.dsp15 years ago

Hello, I have several traces of "flow noise" that I have recorded by locating microphones in a flow field. These are stored as .WAV files on my...

Hello, I have several traces of "flow noise" that I have recorded by locating microphones in a flow field. These are stored as .WAV files on my PC. I would like to process these traces (power spectrum, cross-correlation etc.) and therefore need to get the amplitude Vs. time information out of the WAV files. I just started using libsndfile and made some progress. Not sure how to get at the wa...

## long symbols in IEEE 801.11a

Started by in comp.dsp15 years ago

Hello, I have searched for information for synchronization project and its about IEEE 802.11a preamble.I have one question that is very...

Hello, I have searched for information for synchronization project and its about IEEE 802.11a preamble.I have one question that is very important for me. why do we use both auto correlation and cross correlation together .I mean exactly that we use cross correlation (using known symbol such as long symbols) for symbol timing but for packet detection we use auto correlation.why dont we use...

## Summation problem

Started by in comp.dsp15 years ago 3 replies

In the course of understanding a cross-correlation problem (this is not homework!), I need to evaluate: sum (n = 0 to N) exp (j * n *...

In the course of understanding a cross-correlation problem (this is not homework!), I need to evaluate: sum (n = 0 to N) exp (j * n * theta) or equivalently: sum (n = 0 to N) cos(n* theta) + j * sum(n = 0 to N) sin(n * theta) where N is 150 or so and theta is something rather small, on the order of 0.001 * pi. I'd guess these summations are somewhat common and I could ...

## Time Delay Estimation - LMS

Started by in comp.dsp15 years ago 1 reply

I know how to estimate time-delays using FFTs and generalised cross- correlation but I was wondering if LMS offers any advantages. eg if I have...

I know how to estimate time-delays using FFTs and generalised cross- correlation but I was wondering if LMS offers any advantages. eg if I have say two acoustic sensors I would know the delay by assuming there are 'zeros' in the leading coefficients of the LMS (ie the weights). What mechanism would be used to say what is near to zero? Practically you might have something obvious like 0.01,...

## How to cross-correlate in polar coordinate using FFT?

Started by in comp.dsp15 years ago 6 replies

Hi, We all know the FFT-based cross-correlation in cartesian coordinate is given by: C = IFFT[ FFT[ f(x,y) ] * Conj[ FFT[ h(x,y) ]...

Hi, We all know the FFT-based cross-correlation in cartesian coordinate is given by: C = IFFT[ FFT[ f(x,y) ] * Conj[ FFT[ h(x,y) ] ] Here is the question: how is it possible to do this in polar? I do not think if this is the answer: C = IFFT[ FFT[ f(r,p) ] * Conj[ FFT[ h(r,p) ] ] where f(r,p) and h(r,p) are the polar transformation of f(x,y) and h(x,y).

## circular cross correlation

Started by in comp.dsp15 years ago 2 replies

I need a cross correlation, which is circular along teta-axis and linear along ro-axis XC(H', R') = Σ Σ F(p + H', teta + R')....

I need a cross correlation, which is circular along teta-axis and linear along ro-axis XC(H', R') = Σ Σ F(p + H', teta + R'). G(p,teta ) I have tried several methods but without satisfactory results. Also, I have used the function "imfilter", which does a circular correlation but the result is always the same: bad. I know that teta-axis-circular and p-axis-linear

## Generalized Cross Correlation

Started by in comp.dsp6 years ago 2 replies

Following this thread http://www.dsprelated.com/showmessage/1737dd5/1.php and the code from Davide Renzi...

Following this thread http://www.dsprelated.com/showmessage/1737dd5/1.php and the code from Davide Renzi at http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=8581&objectType=file I tried to implement a simple demo to learn the differences between all GCC methods for time delay estimation. I have some questions and request: 1 - Can someone run this script and tell me ...