Questions tagged [sampling]

In signal processing, sampling is the reduction of a continuous-domain signal to a discrete-domain signal.

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Effect of down-sampling to PSD from auto-correlation?

I have a problem to evaluate the PSD from auto-correlation. As you know, PSD is the Fourier Transform of the auto-correlation. But I observe the spur at PSD when I calculate the auto-correlation with ...
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RSSI of a sampled signal dBFS formula logic

i am trying to understand the logic of the formula bellow. learned before the simple A2D formula resolution=amp/2^bits A2D_value=digitam_number*resolution Is the some material i can read abou this ...
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Symmetric half band filter - redundant oversampling?

I'm making a basic symmetric decimating half band filter (M=2), with alternating 0 coefficients. The signal is oversampled by a factor of 2, at frequency $f$. I must be missing something simple, but ...
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Why HRV is considered as "irregularly time-sampled sequence"?

HRV is heart rate variability. As far as I understood, it is the time interval between two consecutive R peaks in the ECG signal. So an HRV dataset may contain two columns, one containing the interval ...
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What is clock frequency used for?

What is clock frequency used for? for example, a 64MHz microcontroller is used for sampling with a rate of 256 Hz. Why? I think we can use a simpler one with lower clock frequency?
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1 answer
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Conceptual doubt about PID algorithm in PLC

I have to use the PID algorithm that I describe below, obtained from a PLC in the company where I work, so I want to understand it. This is used for control a valve that opens to let gas pass and ...
1 vote
2 answers
77 views

Realtime sample rate conversion from variable source

Having all but given up on getting USB audio to work reliably, I'm looking now at taking the stereo 16-bit I2S stream from the Raspberry Pi 4's 40-pin GPIO header. Unfortunately, that signal stops ...
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Question on discrete signals and quantization

Suppose we have 2 different levels of a quantized signal. Let's say that the range is $[-1,1]$. The number of bits necessary to encode these levels is$\log_2(2) = 1$. However if the value of the ...
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1 answer
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How does the quadrature sampling lower the sampling rate?

According to this tutorial, by exploiting quadrature sampling with IQ signals, we then have the benefit that each ADC operates at half the sampling rate of standard real-signal sampling (This ...
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1 answer
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Strange Look to Sampled Sinusoid [duplicate]

Ok so as part of a project for school I have been designing an FIR bandpass filter. The output should have been a signal which looks like a sampled sinusoid but there was a strange alteration on the ...
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Relation between baud rate and sampling rate and regarding simulation in Simulink

I am new to the field of signal processing. So, this might be a very basic question. Recently, I am trying to build a Heart rate sensor for a cycle. I am mod-ekg (olimex) board with TI's MSP430FG439 ...
1 vote
2 answers
56 views

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 ...
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FFT channelising for DF

I have a 25 MHz IBW real time signal analyser throwing out 25 MHz wide complex data at 50 MHz sampling frequency. I want the frequency resolution to be 12.5 kHz (width of a vhf channel) so need 2000 (...
1 vote
1 answer
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Conceptual clarification of Sampling theorem

I am new to signal processing. We were introduced to the sampling theorem and intuitively I am struggling to make sense of it: There are 3 points I am struggling to comprehend: The analog signal: the ...
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3 answers
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How do you find the null to null bandwidth for the signal below?

My tutor does not explain it very well. Can someone please explain to me the reasoning and what null to null bandwidth actually is?
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accelerometer data processing, time drift and fft

We have have a small data cleaning issue we would like to share. Context: We have data from an accelerometer sensor worn at the hip. We set the device so that data are collected at a sampling rate of ...
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1 vote
1 answer
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How to get a single point of the rising edge of a square wave in relation to its time?

I am trying to get data from only 1 point of each rising edge and trying to relate it to 1 point of the sin wave at the same time. Ideally, the middle of the rising edge is where I want the sin wave ...
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MCMC on unevenly distributed data

So I have this data set, consisting of 100 points. But the problem is that they're not evenly distributed on the time axis. Meaning, I can see a very clear sine wave in the very beginning of the set ...
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Which one is a better impluse response by comparing two given filter length?

I was asked which impulse response $h_1(t)$ or $h_2(t)$ has a better decoding performance for two filter lengths: $l_1 = 50$ and $l_2 = 500$. $$h_1(n) = \cfrac{1}{\sqrt{l_1}}\cos{(0.2\pi n f/f_s)}$$ $$...
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1 vote
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What is the connection between the maximum time-value in seconds, number of samples N and the sampling frequency fs in Hz?

I am working with the following: The script signalsim simulates one realization of a Gaussian stationary harmonic process according to $$x(n) = A_1 \cos (2 \pi \...
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2 votes
2 answers
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Why complex signal doesn't remove "beatings" while sampling?

My motivation to this post has arisen from the accepted answer to Amplitude modulation vs sampling rate? Sampling the signal with the frequency close to $f_s/2$ can lead to some kind of "beatings&...
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Why power = variance = rms^2 in the White Noise process?

I'm an electrical engineering student studying statistics. I saw in an article that White Noise variance = power = rms^2. Could you explain how this expression is ...
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1 vote
3 answers
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Sample Frequency does not matter if it is sufficiently large

I'm not able to convince a colleague on the following topic. Statement: If, and only if, the sample frequency is sufficiently large and above the Nyquist frequency it does not matter what fs is as ...
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Downsampling a binary file

TEXBAT is a recorded dataset about spoofing scenarios for evaluating GPS signal authentication techniques. On this project, there are recorded GPS signals stored as complex 16- bit samples at a rate ...
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3 answers
1k views

Why are the units of a sampled signal Volts*Hertz?

I'm posting here because I don't understand why when we have a signal, let's say a voltage, the units of its sampled values are Volts multiplied by Hertz and not just only Volts? It's something I've ...
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2 votes
1 answer
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Calculating estimated ADC Noise Floor from given specifications

As per my current understanding, the ADC datasheets for modern high speed ADCs give the noise level measurements in terms of Noise Spectral Density (NSD) in unit of dBFS/Hz. Now to convert that value ...
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Why does Python welch give me a different answer from MATLAB's pwelch?

I am trying to implement the following line of MATLAB code: [pxx, f] = pwelch(data,[],[],4096,F_S) in Python. Knowing that MATLAB using a Hamming window type that ...
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When I am acquiring the DFT on collected data, do I need to normalize the sampling frequency?

I have collected data from an oscillating system where angle values change over time and I am interested in identifying frequencies in my oscillations. Given that my sampling frequency is $f_s = 1$ ...
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sampled FT of Continuous time LTI output

I am trying to compute the sampled Fourier Transform of a Continuous Time LTI system output. $x(t)$ is the input of LTI and $h(t)$ is the impulse res. $y(t)$ is the output. we know that $$ y(t) = \...
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Sampling with impulse train

There are many times when the textbooks used by all university students like me make an introduction to the notion of sampling of a continuous-time signal with an impulse train as shown below. Why do ...
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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 ...
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gnuradio , SDR usrpx300

I use usrp x300 SDR. I'm confused about Bandwidth and sample_rate. How do I calculate them? is ...
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1 answer
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Do you append 00 or 10 when oversampling

Say I have an 8-bit ADC and I oversample at such a rate as to obtain 2 additional bits. So, before I apply the low-pass filter, I need to append two extra bits to the 8-bit signal of the ADC. Do I ...
1 vote
2 answers
153 views

FMCW radar and calculating ADC Sampling rate

I am new to FMCW radar and I am using a TI module. I have been reading the TI reference material and they keep mentioning the parameter "ADC Sampling Rate". I am confused by what this means ...
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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:]]), ...
1 vote
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Stability analysis of hybrid discrete-continuous systems

I'm trying to derive the overall state-space system model for a hybrid system, in order to plot its eigenvalues. The system is shown as follows: Which is originally from this paper: Modeling and ...
2 votes
2 answers
171 views

How does the sample rate work on an SDR?

How can an SDR, which has a sample rate of about 32MHz record signals with a frequency of 1GHz? Shouldn't the sample rate be at least two times as high as the frequency or am i missing something?
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1 vote
1 answer
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How to Calculate Frequency "X values" from a FFT/DFT Transformation

First of all I am totally new to the DSP field and I have no background in it whatsoever, but my work in biology has led me to data that would greatly benefit from DSP. Any answers devoid of specific ...
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Upsampling after S/P convertor in MSK modulation

I have found this post "implementation a S/P conversion: different length / in Matlab" In the given implementation, Tsym = 2*ovs. ...
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1 answer
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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 $f+Nf_0$ ...
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Optimum sampling frequency for decoding analog PDM stream?

I have an analog value coded as an analog PDM stream, which has a toggling frequency $f_{PDM} \approx$ 100 kHz when the value is at midscale. I am demodulating this value into a 32 bit result with a ...
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11 votes
5 answers
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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{...
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Quadrature Detector with a single ADC

I have a quadrature detector, which provides I and Q baseband signals with 4 kHz bandwidth, set by detector's LPF. I digitiize them on two ADCs with sampling frequency 48 kHz, make Hilbert ...
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FFT to work out optimum number of samples to average

I have a magnetometer, a LIS3MDL to be precise, and I am taking readings from it every second. As expected there is variation in the readings. For example, if I take five readings I get: 1164, 1190, ...
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1 answer
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Sampling Frequency For Samples That Are Greater Than 1 Second

I understand that sampling @ X times per second is X Hertz. What if the sampling rate is given in minutes? 5 minutes for example. 5*60=300 Is that 1/300 Hertz or 0.003333~ Hertz?
2 votes
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Convolve sinc trains

$$ \begin{align} & \mathrm{sinc}(As + .5)\sum_{n=-\infty}^{\infty} \delta (s - n/A)\ \star \\ & \mathrm{sinc}(Bs + .5)\sum_{n=-\infty}^{\infty} \delta (s - n/B) \end{align} $$ How to compute? ...
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Why would the emitted signal from repeating binary data over a wire appear at a frequency lower than the bit frequency?

I have a signal over which binary data is transferred over wire in a repeating 10 bit format. The wires that the data is send over are CML, DC coupled 3.3V twisted pairs, and the protocol of encoding ...
0 votes
1 answer
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How to maintain DFT symmetry for zero padding in frequency domain? [duplicate]

I am looking for a mathematically correct way of zero-padding in the frequency domain when we have an even number of points. (i) If we zero pad in the center of the DFT, after the Nyquist value, the ...
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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 ...
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2 answers
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Does LPF limit the maximum sampling frequency of the input signal? [closed]

Consider the system where the signal passes through analog LPF with cutoff frequency of 50 Hz, so the maximum sampling frequency of the input signal could be 100 Hz (according to the theorem). But can ...
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