# All Questions

16,633 questions
422 views

### Fourier Transform with both Time Delay and Frequency Shift

I know that the Fourier transform of a function with time delay can be written as: $$\mathscr{F}\big\{x(t-t_0)\big\}=X(f)e^{-j2\pi f t_0}$$ The Fourier transform of a function with frequency shift ...
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### Digital filter design of time series for specified frequency response function

I am currently working with vibration measurements in structures. In the netherlands there is a guideline for verifying vibration measurements for damage to machinery. This is the so-called "SBR ...
16 views

### Sampling Frequency and Spectral Regrowth

Sampling a cosine wave of 10 Hz at Fs = 64 and number of samples Ns = 256 I setup my time vector for the cosine wave as n=(0:Ns-1)*(1/Fs) If I change the sampling frequency from 64 to 64.0005 I get ...
39 views

### Correlation between 2 signals of uneven dimensions

As a part of my work, I am trying to correlate the audio signal in a video with the pixels of each frame. The steps I follow are: Audio sampling rate and frame rate of the video are known. So, ...
60 views

### Simulate time series given temporal auto-correlation functions

Given a random process $x[n] \in \mathbb{R}$ (say of length $N$) and all correlation functions such as: \begin{align} \langle x[i]\rangle\\ \langle x[i]x[j]\rangle\\ \langle x[i]x[j]x[k]\rangle\\ \...
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### Synthesizing a function from a fourier transform

So I have this question in a homework and cannot seem to solve it no matter what I try. Question: Use Matlab to find out what function in time x(t) resulted in the Fourier Series ...
20 views

### how to lower frequency of a soubd file in matlab?

I am new to programming and sound processing, I have been using matlab to process sound files, a few of which are ultrasonic. my sampling rate is 250kHz. I Would like to be able to play the sounds at ...
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### Autocorrelation

What is autocorrelation in real life? Any example? How does autocorrelation dependent on time difference? Here is Xt1 and Xt2 how comes \phi{tau}?
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### DFT of a series of RC exponentials

Context: I'm trying use matlab to apply a single-pole filter to a time-domain ramp waveform that is generated by a sequence of time-shifted "RC steps" that are added together. The time domain voltage ...
77 views

### How can I improve my fit of cosines to periodic data using Python?

I have a space-separated csv file containing a measurement. First column is the time of measurement, second column is the corresponding measured value, third column ...
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### Why is the size of results from FFT half the size of the input, while that is not the case in image processing?

When dealing with real data, Fourier Transform produces symmetric results and FFT algorithms discards half of it. An input with 1024 points will yield only 513 points in the output. However, in image ...
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### vibration analysis in spherical coordinates

I'm trying to understand some data from a vibration sensor, in units of milli-g and in cartesian coordinates. One idea I had was to analyze the data in something like spherical coordinates, to ...
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### How to define and use custom wavelet filters in python?

I would like to define custom analysis and synthesis filters for wavelet implementation in pyhton. How it can be cone using pywt library?
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### Designing Rayleigh Fading Wireless Channel with particular properties [closed]

I have some information on particular wireless channel between an Access Point(AP) and K users as described in the picture below: How i can create this channel in Matlab?
17 views

### response of LTI system to a Random Input Signal

what is LTI filter? what is the output when x(t) is input? let x(t) be the input signal to the system and y(t) denote the output signal. The output of the system may be expressed in terms of ...
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### Artifacts observed in STFTs computed with C++ library FFTW3 or NE10

In one of my projects, I have to compute stfts with audio signals coming either from a microphone or a .wav file in a C++ based program. However, I am observing different artifacts due to my stft ...
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### How to obtain the steady state response of the sampled periodic signal data?

Below the green plot Vin is 5Hz sine voltage signal from a function generator output sampled at 12kHz sampling rate: The blue plot Vout is the processed/filtered data by using the following code in ...
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### GLP type three filter of order k, amplitude response?

Given a GLP type three filter of order K, with an amplitude response of |H(theta)|. I need to show that the number of real and causal FIR filters(identically different) of order K, with the same ...
24 views

### Frequency Resolution Problem

Im trying to tackle the following problem while still not having a firm idea on what "frequency resolution" means : Suppose we sample a continuous time signal with sampling period Ts = 1/2000, and ...
17 views

### Linear equation set construction for Brox et al. optical flow optimization

I'm trying to implement an optical flow calculation program for two successive images based on this article by Brox et al. The Euler-Lagrange combined with a fixed point iteration loop yields two ...
10 views

### Edge detection for bio-film filaments

I have this image of bio-film filaments growing in a matrix and would like to extract just the filaments from the image to calculate the angle at which they are growing. What techniques would be best ...
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### Active Noise cancellation for non periodic signals

I observed that the coded algorithm for active noise cancellation is not able to cancel some of the signals like a human voice. Is there any solution for this? Can we really cancel non-periodic ...
18 views

### Wide-Band Lorentzian FDTD Algorithm

I want to convert a simulated gain/absorption of a material, which can be understood as a discreet (dispersive?) function $g_i(f_i)$ ($f$ is for frequency) or $g_i(\lambda_i)$, into $\tilde g(t)$ for ...
14 views

### Wifi signal stability of routers

In certain routers, there is a setting that allows one to change the interference resistance, which is bounded between the limiting cases of "maximum stability" and "maximum performance." Apparently, ...
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### Services for phoneme recognition?

I wonder if anyone can point me to services or dev libraries that focus on or suit phoneme recognition? Target audience is children at learning to read stage. We have trialed IBM Watson (not good) ...
29 views

### periodicity of constant discrete time signals

are constant discrete time signals periodic? example $$e^{i10\pi n}$$ my proffesor says that this signal is aperiodic, in the discrete sense. but it seems wrong, because ...
21 views

### Error due to downsampling an image

I have two images $I_1$ and $I_2$ suppose $I_2 = downscale(I_1)$, so for example if $I_1$ has resolution 1024x1024 $I_2$ could be 512x512. How can I measure how much quality I've lost during this ...
143 views

### A question on Fourier Series and the frequency of the sinusoids

On studying about Fourier series, I encountered 2 doubts: How is it that a non-periodic function has a Fourier series? When expressing a periodic function as summation of sinusoids, why is the ...
24 views

### DFT sample point k < N has negative frequency

(From: Schaum's DSP outline, 2nd edition, page 254, problem 6.35) A signal $x_a(t)$ that is bandlimited to 10 kHz is sampled with a sampling frequency of $f_s = 20$ kHz. The DFT of N=1000 samples of ...