# All Questions

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### Why is it a bad idea to filter by zeroing out FFT bins?

It's very easy to filter a signal by performing an FFT on it, zeroing out some of the bins, and then performing an IFFT. For instance: ...
1k views

65k views

### What does frequency domain denote in case of images?

I was just learning about the frequency domain in images. I can understand the frequency spectrum in case of waves. It denotes what frequencies are present in a wave. If we draw the frequency ...
62k views

### Variance of White Gaussian Noise

It could seem an easy question and without any doubts it is but I'm trying to calculate the variance of white Gaussian noise without any result. The power spectral density (PSD) of additive white ...
147k views

### Why should I zero-pad a signal before taking the Fourier transform?

In an answer to a previous question, it was stated that one should zero-pad the input signals (add zeros to the end so that at least half of the wave is "blank") What's the reason for this?
18k views

### What Resources Are Recommended for an Introduction to Signal Processing (DSP)?

What are some recommended resources (books, tutorials, lectures, etc.) on digital signal processing, and how to begin working with it on a technical level?
3k views

### About Discrete Fourier Transform vs. Discrete Fourier Series

I am new to the field of signal processing. I am wondering what is the difference between DFS(Fourier Series) vs. DFT(Fourier Transform). For common applications, usually we get a segment(length <...
10k views

Being a non signal processing science student I have limited understanding of the concepts. I have a continuous periodic bearing faulty signal (with time amplitudes) which are sampled at $12\textrm{ ... 1answer 52k views ### Kalman filter for position and velocity: introducing speed estimates Thanks to everyone who posted comments/answers to my query yesterday (Implementing a Kalman filter for position, velocity, acceleration ). I've been looking at what was recommended, and in particular ... 4answers 27k views ### How many taps does an FIR filter need? I am looking to design a set of FIR filters to implement a low pass filter. I am also trying to reduce the latency of the signal through the filter so I am wondering what the minimum number of taps I ... 6answers 15k views ### Flipping the impulse response in convolution During convolution on a signal, why do we need to flip the impulse response during the process? 2answers 7k views ### Frequency shifting of a quadrature mixed signal I've a quadrature mixed signal with 10 MHz as highest frequency available. I want to shift it to any frequency lesser than 10 MHz. I should get it by multiplying this signal by cosine of the required ... 1answer 20k views ### I and Q components and the difference between QPSK and 4QAM Both 4QAM and QPSK apparently produce the same waveform, but are they the same mathematically? In a QPSK constellation, are the mapping points at 45, 135, 225 and 315 degrees while the 4QAM is at 0, ... 2answers 28k views ### Why so many methods of computing PSD? Welch's method has been my go-to algorithm for computing power spectral density (PSD) of evenly-sampled timeseries. I noticed that there are many other methods for computing PSD. For example, in ... 2answers 27k views ### How do I manually plot the frequency response of a bandpass Butterworth filter in MATLAB without freqz function? I have code like below that applies a bandpass filter onto a signal. I am quite a noob at DSP and I want to understand what is going on behind the scenes before I proceed. To do this, I want to know ... 9answers 72k views ### What is the physical significance of negative frequencies? This has been one of the holes in my cheddar cheese block of understanding DSP, so what is the physical interpretation of having a negative frequency? If you have a physical tone at some frequency ... 3answers 62k views ### Why is the FFT “mirrored”? If you do an FFT plot of a simple signal, like: t = 0:0.01:1 ; N = max(size(t)); x = 1 + sin( 2*pi*t ) ; y = abs( fft( x ) ) ; stem( N*t, y ) 1Hz sinusoid + DC ... 1answer 7k views ### Does the autocorrelation function completely describe a stochastic process? Is a stochastic process completely described by its autocorrelation function? If not, which additional properties would be needed? 3answers 47k views ### FIR filter with linear phase, 4 types I know there are 4 types of FIR filters with linear phase, i.e. constant group delay: (M = length of impulse response) Impulse response symmetrical, M = odd Imp. resp. symmetrical, M = even Imp. resp.... 2answers 18k views ### Transfer function of second order notch filter Can anyone mention the transfer function of second order notch filter to remove the line frequency of 50 Hz, in terms of frequency and sampling rate. Just like for Low pass Butterworth filter as, $$... 3answers 3k views ### how to make CIC compensation filter I gotta wrap my head around to design CIC compensation filter I'm studying by referring these materials: Altera, "Understanding CIC compensation filters Hardware Efficient FIR Compensation Filter ... 8answers 134k views ### Why is the Fourier transform so important? Everyone discusses the Fourier transform when discussing signal processing. Why is it so important to signal processing and what does it tell us about the signal? Does it only apply to digital signal ... 3answers 9k views ### How to implement a digital oscillator? I have a floating-point digital signal processing system that operates at a fixed sample rate of f_s = 32768 samples per second implemented using an x86-64 processor. Assuming that the DSP system ... 1answer 3k views ### What is an AMDF? The wikipedia page for Average Magnitude Difference Function/Formula (AMDF) appears to be empty. What is an AMDF? What are AMDF's properties? What are AMDF's strengths and weaknesses, as compared ... 1answer 4k views ### What happens when N increases in N-point DFT [duplicate] I am curious about DFT, and I wrote a simple MATLAB code to test what happens when N increases. I took a rectangular signal with length L=15, an then found th DFT of 16, 32 and 64 points. I looked ... 4answers 191k views ### What is meant by a system's “impulse response” and “frequency response?” Can anyone state the difference between frequency response and impulse response in simple English? 8answers 95k views ### How do I implement cross-correlation to prove two audio files are similar? I have to do cross correlation of two audio file to prove they are similar. I have taken the FFT of the two audio files and have their power spectrum values in separate arrays. How should I proceed ... 12answers 31k views ### Deconvolution of 1D Signals Blurred by a Gaussian Kernel I have convolved a random signal with a a Gaussian and added noise (Poisson noise in this case) to generate a noisy signal. Now I would like to deconvolve this noisy signal to extract the original ... 3answers 6k views ### Pink (1/f) pseudo-random noise generation What are some algorithms for generating a good pseudo-random approximation to 1/f (pink) noise, yet suitable for implementation with low computational cost on an integer DSP? 2answers 2k views ### High modulation index PSK - carrier recovery How to recover the carrier of a PSK signal that has high modulation index (eg. 750 symbols per second at carrier frequency 1500 Hz)? I guess that a PLL will not be able to lock onto it with such ... 1answer 3k views ### Numerically Controlled Oscillator (NCO) for phasor implementation? If I want to simulate a digital oscillator (or phasor) to modulate an arbitrarily length signal:$$y(t) = \cos(2\pi f_ct)\quad\text{where}\quad t = \frac{n}{f_s}\quad\text{for sample}\quad n$$What ... 2answers 43k views ### Step by Step Camera Pose Estimation for Visual Tracking and Planar Markers I have been working on the topic of camera pose estimation for augmented reality and visual tracking applications for a while and I think that although there is a lot of detailed information on the ... 3answers 44k views ### What are the most common algorithms for adaptive thresholding? Adaptive thresholding has been discussed in a few questions earlier: Adaptive Thresholding for liver segmentation using Matlab What are the best algorithms for document image thresholding in this ... 2answers 30k views ### What is the advantage of MATLAB's filtfilt MATLAB's filtfilt does a forward-backward filtering, i.e., filter, reverse the signal, filter again and then reverse again. Apparently this done to reduce phase ... 5answers 16k views ### How to create a sine wave generator that can smoothly transition between frequencies I am able to write a basic sine wave generator for audio, but I want it to be able to smoothly transition from one frequency to another. If I just stop generating one frequency and immediately switch ... 4answers 5k views ### Which time-frequency coefficients does the Wavelet transform compute? The Fast Fourier Transform takes$\mathcal O(N \log N)$operations, while the Fast Wavelet Transform takes$\mathcal O(N)$. But what, specifically, does the FWT compute? Although they are often ... 2answers 16k views ### What is normalized frequency I am working on DSP and finding difficulty to understand the term Normalized frequency often used with DFT & DTFT. What is normalized frequency in DSP ? and how it is different from analog ... 1answer 1k views ### Is the Laplace transform redundant? The Laplace transform is a generalization of the Fourier transform since the Fourier transform is the Laplace transform for$s = j\omega$(i.e.$s$is a pure imaginary number = zero real part of$s$). ... 1answer 116 views ### How determine the delay in my signal practically I am trying to practically determine filter group delay so that I can try to reduce or adjust for it. I have tried all kinds of methods but still can't get the right result. I know that theoretically ... 6answers 48k views ### What is the distinction between ergodic and stationary? I have trouble distinguishing between these two concepts. This is my understanding so far. A stationary process is a stochastic process whose statistical properties do not change with time. For a ... 3answers 20k views ### What algorithm does Google use for its “Search By Image” site? What is your best guess how Google Image Search works? I can upload a photo and can search for similar images. What algorithm does it use to identify similar images? 4answers 43k 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 ... 7answers 21k views ### What is an algorithm to re-sample from a variable rate to a fixed rate? I have a sensor that reports its readings with a time stamp and a value. However, it does not generate readings at a fixed rate. I find the variable rate data difficult to deal with. Most filters ... 5answers 7k views ### Is there a technical term for this simple method of smoothing out a signal? Firstly, I am new to DSP and have no real education in it, but I am developing an audio visualization program and I am representing an FFT array as vertical bars as in a typical frequency spectrum ... 3answers 12k views ### How to resample audio using FFT or DFT I'm down sampling voice audio by first performing an FFT, then only taking the parts of the result that I need, and then performing an inverse FFT. However, it's only working properly when I'm using ... 1answer 2k views ### Fourier transform 4 times = original function (from Bracewell book) I was glancing through "The Fourier Transform & Its Applications" by Ronald Bracewell, which is a good intro book on Fourier Transforms. In it, he says that if you take the FT of a function 4 ... 1answer 2k views ### Location of Matched Filter In a digital communication receiver, matched filter(SRRC filter) is used. In different literatures, the location of the matched filter is mentioned in two different places. One is just after the ADC ... 4answers 3k views ### How to get Fourier coefficients to draw any shape using DFT? I'm teaching myself about Fourier Series and the DFT and trying to draw a stylised$\pi\$ symbol by fourier epicycles as detailed by Mathologer on youtube (from 18:39 onwards), and the excellent ...

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