# Questions tagged [cross-correlation]

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### Calculating an impulse response in a stable environment

I would like to estimate the impulse response of a simple environment (room, two speakers, one microphone). I am aware of the issues/limitations of working with "near" LTI systems. That said, I have a ...
6k views

### Measuring time delay of audio signals

Before anyone yells at me I fully realize that this question has been asked numerous times. I assure you that I've read through the existing questions and answers but I am still confused about part of ...
196 views

### Getting error in fit

I was wondering if anyone had run into the problem of trying to estimate errors in their signal processing on spectroscopic data. I know that many people use spectroscopic techniques to estimate ...
7k views

### Phase Correlation - Poor Performance on Noisy/Blurred Images?

I have successfully tested 1D phase correlation algorithm to determine vertical shift between two synthetic images. When I moved to real images, however, it is not able to detect translation at all (...
376 views

### Cross Power Spectral Density of Unevenly Sampled Data

Here's my problem. The input signals $x$ and $y$ will be having the time value aligned with each other. However, the data are not evenly sampled. I would like to calculate CPSD of both signals. The ...
350 views

### Find the time lag for a wave

suppose that we have a wave which has some peaks in some indexes like 2,12,25,... and otherwise zero. I want to extract the time lag or lags between peaks of a signal. could anyone help me ?
262 views

### Correlation between 2 functions

I have a periodical function $f(x)$ that is sampled in time, at a rate of 1 millisecond. Together with this, I also have a second function $t(x)$. I want to find the correlations between periods ...
582 views

### Normalized cross correlation via FHT - how can I get correlation score?

I'm using the 2D Fast Hartley Transform to do fast correlation of two images in the frequency domain, which is the equivalent of NCC (normalized cross correlation) in the spatial domain. However, ...
4k views

### Finding periodicity of spikes, matlab

In my time series data, I have often spikes with regular periods. Sometimes, I get two or three different periodical spike sequences (two electrical noise sources), some with T1 seconds period, some ...
308 views

### How can I detect clicks/ticks in a wav file?

I have a long recording of a train (here is a small sample) there are a number of clicks as the wheels go over joins in the tracks. I would like to detect the location of these. Looking at the ...
1k views

### get amplitude difference via cross correlation?

im currently comparing 2 signals: A = some music B = A + noise and ive implemented cross correlation in frequency domain via complex multiplication to determine the time offset, which works ...
3k views

### Finding symmetric regions/patterns in image

I have a set of images representing the mean curvature of a human back surface. What I want to do is to "scan" the image for points which have similar, reflected "counterparts" in some other part of ...
866 views

### Is there any example or existing resource for using matlab in audio comparison (cross correlation)?

I am new to MATLAB. I have the audio files A and B, B is recorded using a mic while playing audio file A. The length of file B is different from A. A does not always start from 0 second. My program is ...
705 views

### determine background noise level via cross correlation

The setup: Sound is being played by the speaker on the iphone. At the same moment i record sound via the microphone. Obviously the speaker sound will be recorded in addition to all the external noise. ...
514 views

### Why is there a mismatch between normalized cross-correlation and perception for basic waveforms?

To my ears, sawtooth and square waves are more similar to each other than either one is to a triangle wave. However, when I compare their magnitude spectra against each other using normalized cross-...
173 views

### When might looking at rising edges perform better than cross-correlation?

A simple question as the title indicates: Let us assume that we have two signals, measured from two different sensors that are close together. (For this application, the sensors are measuring blood/...
408 views

### Using reference objects to estimate the point spread function?

I have a well-defined object and a clear image matrix of it. In subsequent frames the object moves, causing motion blur. I want to use the object as a reference to "guide" the deconvolution and ...
2k views

### Finding Peaks in an Autocorrelation Function

I'm trying to find the period of a signal. I've used FFT to compute the autocorrelation of the signal. As can be seen from the autocorrelation function (plotted below) I obtained, there are 70 sample ...
2k views

### Time delay estimation of two sensor signals

I have two sensors which are placed around 30 to 40 cm apart , both of them measure the same signal say 'lambda signal'. so there is a delay in the measurement of the signal from the second sensor. ...
46k views

### What is the difference between convolution and cross-correlation?

I've found on multiple sites that convolution and cross-correlation are similar (including the tag wiki for convolution), but I didn't find anywhere how they differ. What is the difference between ...
2k views

### Directly compare subpixel shifts between two spectra — and get believable errors

I have two spectra of the same astronomical object. The essential question is this: How can I calculate the relative shift between these spectra and get an accurate error on that shift? Some more ...
6k views

### Meaning of the Transpose of Convolution

I have an $n \times n$ asymmetric convolution kernel, $k(t_1,t_2)$. $k$ is zero everywhere except for in small regions near the corners. I also have an $n \times n$ image, $f$. Let $*$ denote ...
6k views

### Is up-sampling prior to cross-correlation useless?

Consider a simple case where two signals from two different sensors are cross-correlated, and the time-delay-of-arrival computed from the absissa of the peak of their cross-correlation function. Now ...
2k views

### Finding the Wiener filter transfer function

I am trying to understand the mechanism of finding the transfer function for a Wiener function. ...
14k views

### Time delay estimation of oscilloscope signals using cross correlation

I have recorded 2 signals from an oscope. They look like this: I want to measure the time delay between them in Matlab. Each signal has 2000 samples with a sampling frequency of 2001000.5. The ...
2k views

### What is the difference between normalized peak of correlation, versus peak of correlation divided by its average?

Given a template, and a signal, the question arises as to how similar the signal is to the template. Traditionally a simple correlation approach is used, whereby the template and a signal are cross-...
782 views

### Probability distribution of windowed cross-correlation

This question is in the context of time-delay estimation. Say I have a stationary Gaussian stochastic process $g$, and I know its autocorrelation function $R_g(\tau)$. To do time-delay estimation, I'm ...
3k views

### Synchronizing Two Audio Tracks

I would like to implement an algorithm that synchronizes two audio tracks. The two tracks are very similar; you can imagine they are two recordings of sound (not necessarily music) from two ...
5k views

### Examples of Independent and uncorrelated data in real-life, and ways to measure/detect them

We always hear about this vector of data VS this other vector of data being independent from each other, or uncorrelated, etc, and while it is easy to come across the math regarding those two concepts,...
277 views

### Coarse summary of various methods for detecting when a signal 'starts'

My question is basically in regards to how to detect when (in time) a signal 'starts', and it might also be called 'transient detection', or, as I have read in some papers regarding music, the 'onset' ...
1k views

### Implementing a Matlab filter to cancel cross talk between two sensors

I have two sensors that have a cross talk between them. I would like to cancel the cross talk. For this I recorded two tracks, where sensor no.1 (called x1) has some input, and sensor no.2 (called x2) ...
2k views

### What is the cross-correlation of a WSS signal and the LTI filtered signal?

I remember a result about the cross-correlation function of a stationary signal and that same signal, filtered through a linear time-invariant filter. There might have been an assumption that the ...