Questions tagged [nyquist]

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What's Nyquist frequency in DFT?

I'm currently studying digital signal processing at university but I can't figure out what the Nyquist frequency means in the DFT coefficients, I know what the Nyquist frequency is in the sampling ...
minghierid's user avatar
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Why a sampling frequency would distort a signal even if it meets nyquist theorem [duplicate]

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giraffe123's user avatar
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How does the sampling rate of a digital filter limit the sampling rate that can be used for replay of filtered signal?

I need a band-limited white noise to characterize a biological sensor that senses mechanical movement. For that, I am generating a Gaussian white noise (MATLAB Communications toolbox) of length 10 ...
chinmayeelm's user avatar
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Nyquist plot of $1/[s(s+1)(s+2)(s+3)]$

I am trying to learn how to plot by hand Nyquist plots. I took $$G(s) = \frac{1}{s(s+1)(s+2)(s+3)}$$ I converted it to $G(jw)$ : $$G(jw) = \frac{i w (-11 + w^2)}{(1 + w^2) (4 + w^2) (9 + w^2)} + \frac{...
tonythestark's user avatar
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Two synthetic signals with same frequency result in two different spectrogram results

I have two signals of the same wave $f(t)=\sin(2\pi\cdot 70\cdot10^6 t ), t \in [0,1e-3] $, which I created with Matlab synthetically. My first signal has 1e6 samples and the second has 1e5 samples. <...
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Nyquist Rate - Computing

Good morning, i had a question regarding the Nyquist rate : Let's say i have a signal $x(t)$ with Nyquist Rate $w_0$. I need to find the Nyquist rate of the following two signals : $$(x * z)(t) \text{ ...
Ravinala's user avatar
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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 ...
Link Coquin's user avatar
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Is there a test/statistic for the reliability of my data given my sampling?

I'm in a situation where I'm sampling blood pressure data over time (unequal sampling) to capture potential peaks. On average, the frequency of circadian blood pressure would be 1. But in reality, ...
Gary Stu's user avatar
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Combining two time series with different cadences (different Nyquist frequencies)...?

If it helps, I want to do perform the below computation in python. Two time-series - 30-min cadence (Nyquist of 24 cycles / day) lasting 27 days, followed by 10-min cadence (Nyquist of 72 cycles / day)...
Prasad Mani's user avatar
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modulation transfer function and ground resolved distance

I am trying to understand something in remote sensing but lack a background in science and technology so it is difficult. Hopefully this is a reasonable question to ask. In sensing there are different ...
napoleon4269's user avatar
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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 (...
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Choice of $N_{terms}$, frequency grid in Lomb-Scargle periodogram

I am completely new to signal processing! Please explain as if speaking to someone who knows nothing more than linear algebra and what a Fourier transform is defined as. I am working with an 8-month ...
Akash Dutta's user avatar
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Find constants such that the Nyquist criterion is satisfied [closed]

I have been given the following spectrum, and I want to find a and b such the pulse satisfies the Nyquist criterion, given that the bandwidth of the pulse is 2 kHz and the sampling frequency is 3 kHz. ...
Gustav's user avatar
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How to compute the ifft of a constant value?

I am clearly missing something obvious here because I am trying to do something that ought to be very simple: compute the ifft of a continuous signal. My understanding is that the ifft of a continuous ...
Darcy's user avatar
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Time-interleaved ADCs, Nyquist zones et al

I am trying to decipher some notes on a Time-interleaved Analog-to-Digital Converter with 4 sub-ADCs (the author is unreachable at the moment), but there are few things obscure to me so I was hoping ...
gangrene's user avatar
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recreating nyquist regions using FFT python

using python I have sampled a signal and made FFT to see the spectral picture of the time domain signal. the plot bellow shows only 1st and 2nd nyquist zone. I want to expend the spectral image and ...
lub2354's user avatar
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A problem about SQNR, PCM, DPCM, and DM

A baseband analog message signal $x(t)$ with bandwidth 20 kHz, power $10^{-3}$, and $|x(t)| \leq 1$ is waveform encoded and transmitted through a channel of bandwidth 160 kHz. Besides, let the sampled ...
Wei-Cheng Liu's user avatar
2 votes
1 answer
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Question about Nyquist sampling - filtering of high image copies

Suppose I sample an audio signal with a sampling frequency > twice the highest audio frequency. ie, the frequency transform of the sampled signal looks like the image on top here, where there is no ...
Ameet Sharma's user avatar
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How do I match a filter to an AWGN channel?

I have the task to find a transition that fulfills the first Nyquist Criterion. After that I am supposed to match that filter to an AWGN channel. For the first part I thought a raised cosine ...
Ole's user avatar
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LTI Filter for DAC Reconstruction

$\textbf{Question:}$ An analog-to-discrete is designed as, $$x[n] = x_a(nT)$$ In an attempt to recover the analog signal from its samples x[n], a D/A converter is designed as , where $x_1(t)$ is ...
Ahsan Yousaf's user avatar
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Why does the bandwidth of a signal need to be half of the sampling rate? [duplicate]

Suppose I perform a DFT on some function with sampling rate of $\frac{1}{\Delta t}$. According to this page, the bandwidth, which is the maximum frequency that can be analyzed when performed the DFT, ...
userflux9674's user avatar
6 votes
3 answers
2k 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? ...
W_vH's user avatar
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Discrete Fourier Transform of real valued input using half the amount of frequency bins

Quick question: Is it correct to define Discrete Fourier Transform like this, if my input signal is real valued: $$ X[k] = \sum_{n=0}^{N-1} x[n] \cdot e^{-i2 \pi n \frac{k}{N}} $$ Where $k \in \{0, 1, ...
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Nyquist frequency Plotting Distortions

I'm trying to plot some sinusoidal signals in Matlab. But while frequency is getting higher (closing to fs/2), results are getting distorted. I guess it's lack of my knowledge but distortion is ...
BugraKezan's user avatar
5 votes
2 answers
677 views

Is there a way to compute the spectrum effect of a non-linear function?

I'm interested in developing audio software. I've read the books by Will Pirkle and there's something I'm struggling to understand about how non-linear functions affect the frequency spectrum of a ...
U62's user avatar
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3 votes
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Filter amplifies frequencies at nyquist frequency. What's the purpose of such a filter?

I'm currently facing a filter that amplifies frequencies at the Nyquist frequency. The sampling frequency is $f_s = 10$ Mhz. What's a typical application for such a filter? This is how I generated ...
Julian Sarcher's user avatar
2 votes
1 answer
186 views

How does a CIC filter output meet Nyquist?

In this image from Understanding cascaded integrator-comb filters The bottom image shows the output response, with the entire range as passband: Even the CIC compensation filters are all passband to $...
user37216's user avatar
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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 ...
drC1Ron's user avatar
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Are there any recommended filter types for passband frequencies near Nyquist?

Is there a recommended filter type for frequency bands near the Nyquist frequency? I have been trying to design complex passband filter with passband $[0.8 ~~1]$ ( where $1$ corresponds to the ...
Hilbert's user avatar
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3 answers
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Why are real-world digital images not bandlimited?

In the materials about image resampling, it always mentions that real-world digital images not bandlimited. However no explanation is provided. For example, Sinc resampling in theory provides the ...
Jogging Song's user avatar
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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:]]), ...
OverLordGoldDragon's user avatar
4 votes
1 answer
777 views

How is the maximum theoretical data rate of a channel equal to $2B\log_2(V)$ bits/sec.?

According to Andrew S. Tanenbaum (in "Computer Networks", Chap. 2, Section 4 "The Maximum Data Rate of a Channel"), the Nyquist/sampling theorem states that "if an arbitrary ...
j3141592653589793238's user avatar
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1 answer
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How to choose correctly oversampling ratio?

As many of us have noticed, last two months I am working on GMSK modulation and demodulation design. Before continuing my research, I want to be sure I chose the correct oversampling ratio ( how many ...
FrimHart64's user avatar
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1 answer
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Reconstructing a signal from a Nyquist plot

I have a system which is like a blackbox which has just one input which could be a sinusoidal wave which is a sum of a range of frequencies, now the problem is that I dont have the time-domain output ...
Novice_Developer's user avatar
1 vote
1 answer
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What does the two following formulas mean?

I am a bit confused between the following two formulas: $$ f\le \frac{f_s}{2} \tag{1}$$ and: $$ f = \frac{f_s}{N} \tag{2}$$ Now I am given an ACF Plot of a sine/cosine wave and I am asked to find ...
Muhammad Ahmad's user avatar
3 votes
2 answers
1k views

How do we determine the required sampling rate of a closed loop control system?

Consider the controlled dynamical system $\dot{x}_t = f(x_t, u(t-\tau_{sd}))$, where $0<\tau_{sd}$ denotes the time delay caused by sampling. It is intuitively clear that the time delay caused by ...
kbakshi314's user avatar
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1 answer
527 views

What is the output signal's frequency when doing operations of two signals?

If I have two continuous time signals x(t) and y(t) of maximum frequencies Ω1, Ω2 respectively. I want to find the sampling frequency used used in continuous-discrete conversion of the following ...
April Crude's user avatar
1 vote
1 answer
113 views

How do I determine the dominant frequency of a signal after sampling?

For example if I have a $10 Hz$ signal and I sample it at $19 Hz$ (less than the Nyquist frequency) how can I determine the dominant frequency of the output and why? If I then apply a lowpass filter, ...
Major Anarchy's user avatar
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1 answer
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Sampling, filters, windowing, FFT. From theory to help on this coding list

My plan is to analyse the spectrum of samples from a microphone. I wonder how correct this suggestion is. The below description may then fail on several points. I am in need of somebody with a red ...
Øyvind Teig's user avatar
4 votes
3 answers
722 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 ...
Abundance's user avatar
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4 answers
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Given a signal that is not bandlimited, how do you properly take the FFT?

I assume that the Nyquist theorem doesn't apply, at least not in the standard sense, for a non-bandlimited signal. In my case, I sample the signal (in the time domain) above the Nyquist rate and then ...
user avatar
2 votes
1 answer
195 views

In what cases can you get aliasing below the Nyquist frequency?

I took the one-sided FFT of a signal and plotted up until the Nyquist frequency. Then, I took the real part of this FFT multiplied by $i\omega$ following a calculation that I'm trying to do of a ...
user avatar
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1 answer
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Matching Filter & Raised Cosine Confusion

I'm reading from Communication Systems, 5th Edition by Simon Haykin. At some point we derived that Which is how the effect due to AWGN is minimized. Meanwhile, to minimize ISI we need $P(f)$ to be ...
Essam's user avatar
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The raised cosine spectrum and Nyquist's criterion for zero ISI

For the past hour, I've been trying to understand what the book is trying to say here: This is Communication Systems, 5th Edition by Simon Haykin. We know that the Nyquist criterion is I'm unable to ...
Essam's user avatar
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1 answer
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Inferring shape of information signal from its DFT?

I came across this question recently, and I am very confused by (b)(ii). b(i) gives $x_n$ = [0.5, 0, -0.5, 0]. My approach to (ii) was to recognise that $X_m$ represents the frequency content of the ...
VJ123's user avatar
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What is the symbol rate achieved with raised cosine filter?

The bandwidth of the raised cosine filter is w=0.5(1+r)Rs, where Rs is the symbol rate, and r is the roll-off factor. r=0 represents the Nyquist filter, for which Rs=2w. Any higher value for the roll-...
Noha's user avatar
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3 answers
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Will or can a sampled signal with a limited sampling frequency have infinite bandwidth?

I know that a continuous-time digital signal with sharp edges (e.g. jumping from one y-Value to another discontinuously at the same x-value) will have infinite bandwidth. But what about sampled ...
Soeren's user avatar
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does T = 1/F always hold?

i just want to know if i use a sampling frequency of 100-110Hz and get a useful signal frequency of 50Hz (because of Nyquist–Shannon sampling theorem), is the period 1/50Hz or 1/100Hz? I've been told ...
B.Adlane's user avatar
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Sampling frequency vs Signal frequency

I've started recently working with the ADXL345 accelerometer with the goal of finding the velocity. And so far, I'm getting "okay" results after applying a second-order Butterworth filter to ...
B.Adlane's user avatar
-1 votes
1 answer
319 views

Sampling with Rectangular Pulse and Nyquist Condition

The classical Nyquist theorem assumes that the sampled signal is obtained by multiplying the signal with dirac-delta functions separated by width 1/f_sample or less. Given such sampling we can ...
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