# Questions tagged [aliasing]

In signal processing and related disciplines, aliasing refers to an effect that causes different signals to become indistinguishable (or aliases of one another) when sampled.

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### Ratio of aliased to desired energy of a sampled signal

In this article "Sampling: What Nyquist Didn't Say, and What to Do About It" from Wescott, the author shows in Figure 6, the plot of the frequency spectrum of a signal which goes through a ...
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### Help figuring out how to extract audio content correctly from a file that produces spiky waveform with audible hiss/noise

I'm trying to extract PCM wave sequences from different files (files that are NOT audio files but contain audio data, and other data all in one file), and while this code does extract the expected ...
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I want to measure a signal whose frequency spectrum is infinite, but I am particularly interested in the frequency range $0 - 500 \ \text{Hz}$. I have a 12-bit ADC. The ADC has dynamic range $6 \ \... 1 vote 1 answer 117 views ### Sampling a sinusoidal signal smaller than Nyquist rate If we have a sinusoidal signal at 50 kHz and we sample it by an ADC with a sampling rate of 7 kHz. What would be the output of the ADC? Since the sampling rate is way less than the Nyquist rate (... 1 vote 0 answers 32 views ### Filter choice for the signal with the possible time jitter in sampling and frequency aliasing I'm trying to filter data from the force sensor mounted on the end effector of the industrial robot arm. Mechanical vibration caused by the robot's motion (possibly by actuators, reductors, etc.) ... 2 votes 1 answer 185 views ### Can time aliasing cause peaks? For the following I use the terms “time domain signal” and “frequency domain signal” as a Fourier Transform pair. The question is for generalized cases of continuous-time signals that once sampled in ... 0 votes 1 answer 62 views ### Aliasing problem with pressure data I have done some pressure measurements of flowing air with transducers that had a frequency response of 5 kHz. The data from these transducer was sampled also with 5 kHz and this is where my problem ... 5 votes 2 answers 786 views ### How to measure aliasing? Aliasing is bad, and we want good filters when downsampling. While what qualifies as aliasing is well-defined mathematically, and we can manually design filters with various tradeoffs, how do we ... 5 votes 2 answers 361 views ### How to avoid harmonic distortions in a DAC? I have a DAC which is assumed to be nonlinear, such that it produces unwanted harmonic distortions at integer multiples of the input frequencies. (EDIT: Any other nonlinear distortions, such as ... 0 votes 1 answer 94 views ### Difficulty Understanding a Triangular Graph: Aliasing of Signals I have been reading a textbook on the "fundamentals" of signal processing but the author of the textbook has not given any explanation for the triangular graph located at the bottom of the ... 12 votes 2 answers 1k views ### Where are these aliasing artifacts coming from in transmitting audio? (Frequency reflection, duplication) I am trying to understand how a SIM7600G 4G modem degrades the audio when configured for 8 kHz sampling rate. I created a reference audio using librosa.chirp to slowly sine sweep from 30 Hz to 3400 Hz.... 0 votes 1 answer 63 views ### proof of alias matlab sin wave and syntax for time array I have been asked to prove the following; Show that a sinusoid of amplitude 10V and frequency 2kHz sampled at %fs = 10kHz is an alias of a 500Hz sampled signal. I have develped the code for the 500hz ... 1 vote 0 answers 75 views ### Azimuth image extent in frequency domain SAR algorithms (RDA, omega-k) When looking at the practical implementation of frequency domain SAR imaging algorithms like the range Doppler algorithm (RDA) and the omega-k algorithm (also called range migration algorithm, RMA) as ... 2 votes 2 answers 143 views ### Reconstruction of a Ricker Wavelet using inverse discrete fourier transform - signal cut in a half? I am new here and new to DSP, so maybe my question is really basic. I have the formula for the Ricker wavelet (Mexican Hat) in frequency-domain and I wish to do an inverse Fourier transform to recover ... -1 votes 2 answers 92 views ### Is square of signal more recoverable than signal itself? Let$x[n]$be aliased sampling of real-valued$x(t)$over$t_0 \leq t \leq t_1$. Can$|x(t)|^2$be recovered more accurately than$x(t)$, over$t_0 \leq t \leq t_1$? If so, how? For$|x[n]|^2$, ... 0 votes 1 answer 49 views ### Sampling frequency to use with irregular signal I have experimental data where I collected data points over time and my "signal" looks oscillatory in nature (y-axis values are more or less constrained in a y-axis bandwidth), but the curve ... 1 vote 1 answer 143 views ### Reconstructing an undersampled signal by cutting off at the signal's maximum frequency Assume a (continuous) band-limited signal$f$, that is, a signal for which$F(s) = 0$for all$\lvert s \rvert > p / 2$. If the signal is sampled with frequency$p$, we can reconstruct it by ... 3 votes 0 answers 73 views ### Strange signal processing: is this chaos or spectral aliasing? In the context of DFT calculation, I would like you to explain me why I get this red curve: I work with a DFT simulator I built myself in Python. When I plot the output$y[t]$with the impulsional ... 1 vote 1 answer 89 views ### Is my solution correct?$\textbf{Question:}y_a(t)$is a rectangular waveform defined as: $$\ y_a(t) = \begin{cases} 2 &t \in [0,1/25)s\... 1 vote 1 answer 96 views ### How can I find x_r(t) in this case?$$x_a(t) = 10 + 4\cos(30\pi t +\frac\pi 3) - \sin(250\pi t + \frac 14) -3\cos(500t + \frac \pi4) $$\textbf{Question:} This signal is first sampled at a rate of f_s = 100 samples per second to ... 6 votes 3 answers 1k views ### Moving average before downsampling: effect on Nyquist frequency? First the simple questions: Is there an effect on the Nyquist frequency when I apply a moving average filter on the raw data before I downsample? And what does this do to aliased frequencies? ... 0 votes 1 answer 66 views ### Intuition for how much ringing a particular filter will induce I've seen figures in various books about the the tradeoff between aliasing and blurring when using a gaussian-like filter: the narrower it is, the more it cuts off low frequencies and thus blurs it, ... 2 votes 1 answer 250 views ### Why 5Hz aliasing with LPF implemented I have a simple signal chain with a differential sinusoid as the input. This passes through the first amp which converts the signal to a single ended signal. The next block is a 4 pole low pass ... 1 vote 1 answer 109 views ### How do I estimate possible aliased frequencies in sampling limited measurements? Say I've got some data made from measurements with a too infrequent sampling rate; I know for certain there is aliasing. What I'm interested in is figuring out what frequencies are likely present ... 12 votes 3 answers 914 views ### Other end of Nyquist limit Say I perform FFT on some data. If the underlying (measurement) sampling rate is not twice the highest frequency, I will almost assuredly get aliasing. This limit on sampling we call the Nyquist limit.... 1 vote 1 answer 81 views ### What will happen when we reverse an analysis/synthesis system? Suppose that we have four filters H_0(z), H_1(z), F_0(z), and F_1(z) forming a classic perfect-reconstruction 2-channel filter bank: Will the perfect reconstruction still be achieved if we ... 0 votes 0 answers 41 views ### Is the slow waveform an alias - and why don't we see other alias'es of different frequencies? The following figures are data from sampling the DC bus of an inverter for a BLDC/PMSM drive running a speed-loop with FOC. The upper subplots are FFT's of the signal and the lower subplots are of the ... 0 votes 1 answer 169 views ### Having Nyquist bin = aliasing? Here I motivate the question by deriving FFT upsampling for N \rightarrow 2N with even N. One might naively try xup = 2*ifft([xf[:N//2], zeros(N), xf[-N//2:]]), ... 0 votes 1 answer 92 views ### Sampling and Aliasing What is meant to be explained in the section between the 2nd paragraph and the folding section in the Sampling sinusoidal functions section shown in this link? Why is Nf_0 written in f+Nf_0 ... 12 votes 5 answers 1k views ### What is the frequency representation of nonuniform sampling? Uniform sampling can be thought of as multiplication of a function x(t) with a Dirac comb function:$$\text{III}_T(t) = \sum_{k=-\infty}^{\infty}\delta(t-kT)$$Multiplication of x(t) with \text{... 4 votes 3 answers 718 views ### Stanford EE 261 HW6 Q1 - Sampling below Nyquist Rate The problem (taken from here) asks for possible sampling rates that will not cause aliasing in the following frequency spectrum: The range of possible values after some math is given as B_2 < f_s ... 1 vote 1 answer 104 views ### Removing aliasing from recorded signal I am recording a signal from a vibration sensor with a frequency response that stops at about 7kHz, but linear up to 1kHz. I am thus recording data from it using an Arduino at 2kHz, so that signals up ... 0 votes 2 answers 68 views ### Aliasing in continous-time signal I have the following signal and it was plotted with a sampling frequency (Fs) of 5Khz and F0 was then varied for 0.5Khz, 2Khz, 3Khz, and 4.5Khz. I obtained aliasing when F0 = 2Khz and 3Khz only. ... 0 votes 1 answer 229 views ### How to visualize frequency domain of signal with multiples of f_s? Is it possible to visualize signal in frequency domain for frequencies bigger than f_s? I'd like to get the plot of some example signal like that: I tried to create some signals in ... 2 votes 1 answer 88 views ### Noise from irregular sampling pattern In this paper the author says By using an irregular sampling pattern and filtering the irregular samples to create the pixels, featureless noise is produced from such high frequencies rather than ... 0 votes 1 answer 33 views ### Running a signal through a circuit with some odd components I am studying a course in signal analysis and systems. Currently we are looking at aliiasing, samplig,DTFT and reconstruction. I got stuck on an excercise. For the in signal x_{a}(t)=2\cos(2\pi F_{0}... -1 votes 2 answers 65 views ### What should be my sampling frequency for a peak detector output where it is extremely important for me to capture the first time the peak occured? Following is the output of the peak detector: The amplitude is not important to me, however the time when the peak occurs is extremely important. So my microcontroller will have an algorithm like ... 5 votes 2 answers 276 views ### Nyquist frequency isn't working The situation is that I have a signal with linearly increasing frequency,$$\text{sin}(2\pi\omega(t)t),$$where \omega(t)=a+bt for some a and b, and we constantly sample at one point per second ... 0 votes 1 answer 565 views ### Resampling pitch shifter I’m trying to build a very basic resampling pitch shifter which reads samples from disk. I only want to change -+6 semitones without keeping the original sample length. I already have all the classes ... 1 vote 1 answer 277 views ### How is sampling affecting this sine wave? I am trying to create a sine wave in python, but when I graph it, it looks like this: here is the code I used to make the signal: ... 2 votes 1 answer 846 views ### Aliasing in Doppler Radar my book about RADAR says that: If a Continuous wave radar sends a sine wave at frequency f_T to a moving object (at speed V), a frequency f_R is received. Their difference is called Doppler ... 0 votes 1 answer 60 views ### Digital lowpass filter causing aliasing I'm writing a biquad filter program in C++, using the RBJ Cookbook as the source for the formulas. https://www.w3.org/TR/audio-eq-cookbook/ The lowpass filter that I've made seems to half work. The ... 1 vote 1 answer 82 views ### How to verify and plot expression for sampled signal is correct? Given the signal x_a(t)=4cos(2\pi\times40t+\pi/3)+10cos(2\pi\times160t-\pi/6), I am to sample it at f_s=200Hz and find the expression for x[n] My process:$$x[n]=x_a(nT)=x_a({n\over f_s})=4cos(0.... 0 votes 1 answer 80 views ### Aliasing Issues in Sub Band Coding The general structure of Sub-Band Coding (SBC) is shown below: The diagram shows that after each of the analysis filters, decimation is performed by a factor M which corresponds to the number of ... 0 votes 1 answer 202 views ### Band limited discrete signals division If I take two analog, band limited signals$ x(t) $and$ y(t) $with non-zero$y(t)$I can define the division: $$z(t) = \frac{x(t)}{y(t)}$$ In general$z(t)$may have a very wide bandwidth, also ... 2 votes 1 answer 155 views ### Is spectral density conserved after aliasing? Will the integral of the PSD of a down-sampled signal still equal the variance in all cases 1 vote 1 answer 160 views ### Aliasing below$f_s/2\$

phi = exp(linspace(0, log(511), 1024)) - 1 x = cos(2 * pi * phi) Above will alias, despite peak instantaneous frequency evaluating to ...
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### Condition for aliasing

Which one of the following is the condition of aliasing? (a) Tails of the replicas enter into the Nyquist interval (b) The tails of the replicas enter into the Nyquist interval and add to the ...