Questions tagged [sampling]
In signal processing, sampling is the reduction of a continuous-domain signal to a discrete-domain signal.
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Multiple different length Windows for high resolution realtime FFT
I am looking at trying to achieve a 'realtime' (as quick as possible to acquire, process and present data) FFT application to analyse audio.
I have setup my app to acquire a set of samples, apply a ...
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1answer
19 views
Modulation upsampling method
I try to implement a qpsk modulator in Octave.
The chain is the state of the art I guess: Mapper -> Upsampling x4 -> Root raised cosine filter.
My main question is about the upsampling.
I try to ...
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1answer
282 views
Phantom harmonics when using cosine windows why do they appear and how to avoid them?
Given an L order cosine window, it is possible to show that the width of the main lobe is given by:
$$\omega_w = \frac{2 \pi L}{(2N+1)}$$
Where $L$ is the order of the window, $N$ is the maximum ...
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3answers
1k views
Aquila DSP C++ Library - Wave file FFT analog frequency off by factor of 4?
I'm working with the Aquila C++ DSP library. I'm computing the FFT of a wave file (16 bit depth, single channel, 44100 sample rate). I am using a window size of 16384 to calculate the FFT spectrum.
I'...
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2answers
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sampling a sinusoidal signal at the Nyquist rate
To sample a sinusoidal signal at the Nyquist rate, we have to take two samples per cycle. Is there any condition on the position of the two samples? is it necessary to take them at the peaks?
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59 views
Cancelling out known signal with sampling offset
I would like to cancel out a known audio signal at my receiver.
Specifically at my transmitter I am playing a song, and at my receiver I am recording it. Both transmit and receive sampling rate is 44....
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0answers
19 views
Filtering a noise of F[sig] frequency [Example 20Khz] in measurement system
I am developing a system where there is inherent noise of F[sig] frequency. This is a DC measurement system and want to get rid of the noise by sampling at F[samp] samples per rate and taking multiple ...
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1answer
28 views
Sampling the Wave Equation for String Vibration
I am having a difficult time understanding the basic principles when sampling the function describing the vibration of a string. Mainly I am confused on given a sampling rate how many samples to take ...
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1answer
62 views
How to describe correlated noise after the signal is oversampled?
The Gaussian noise in discrete signal models is usually assumed to be independent and identically distributed variables (i.i.d.). Does this mean that the signal must be sampled with the sampling rate ...
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1answer
155 views
about sampling frequency
I am trying to make a DFT on a signal with frequency f=50 MHz main component plus some noise.
As far as I know if I sample it at F=100MHz I should be able to get a proper plot of the DFT since F=2f ...
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1answer
72 views
Reconstruction of sampled band-pass signal
I am pretty new to signal processing. I am currently trying to reconstruct a sampled band-pass signal created with the filtfilt and ...
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1answer
40 views
How to convert ofdm symbol to signal?
Hello may I know how to convert ofdm symbol generated from ifft block to an OFDM signal for the purpose of transmitting it?
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Where does the imaginary part of a singnal come from? [duplicate]
So I recently watched this lovely overview of DSP/SDR explaining how demodulation of AM and FM becomes trivial by turning a signal into a complex number. (AM being the magnitude of the number and FM ...
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1answer
82 views
IQ Sampling and Oversampling Differences? *Confused*
Two different thought process that produce two different alias band calculations .... What concepts are these?
If I have two 1 GHz ADC's and they sample with 90 degree offset (A comment said this is ...
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1answer
32 views
IDFT - influence of sample numbers
I'm quite a newbie in dsp domain, and there's something I can't understand clearly.
I'm doing a IFDT of a spectrum regularly spaced with complex values : the spectrum is a complex conjugate symetric ...
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1answer
38 views
going from output of D/C to input of D/C
$$y_c[n] \longrightarrow \boxed{D/C} \longrightarrow y(t)$$
If the following equation describes the IDEAL D/C converter:
$$y_c(t) = \sum \limits_{n=-\infty}^{\infty} y_d[n]~ \text{sinc}\Big(\pi (t - ...
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4answers
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“Complex sampling” can break Nyquist?
I have heard anecdotaly that sampling complex signals need not follow Nyquist sampling rates but can actually be gotten away with half Nyquist sampling rates. I am wondering if there is any truth to ...
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1answer
21 views
Multisampling of an ADC channel in a PWM cycle in TI C2000
I want to sample an ADC channel multiple times in one PWM cycle.
I can trig any ADC channel in anywhere in my PWM timer counter now. But I want to trig and sample same channel in many times within a ...
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1answer
98 views
Sampling period
The signal $x(t)=e^{-t^2}\text{sinc}(t)$ was sampled at interval $T$. It was then found that the discrete time Fourier transform of the sampled signal is: $X(e^{j\omega})=1$. What is the minimum $T$ ...
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2answers
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How to calculate sine wave SNR from oscilloscope
I'm trying to calculate the SNR of a sine wave produced with a 12 bit DAC. I'm new when it comes to calculating/measuring noise in signals. My idea was to capture the signal using an oscilloscope (...
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0answers
132 views
How to Extrapolate a 1D Chirped Signal?
Following a past question, I'd like to extrapolate a signal like the one below: (red is signal, blue is the the extrapolated )
...
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4answers
15k views
How to Extrapolate a 1D Signal?
I have a signal of some length, say 1000 samples. I would like to extend this signal to 5000 samples, sampled at the same rate as the original (i.e., I want to predict what the signal would be if I ...
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1answer
61 views
Convolution : Anechoic Speech signal and Impulse response
I am trying to perform convolution in MATLAB of an anechoic speech signal (2.1 s) and a impulse response (20 s) using the following code:
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2answers
495 views
why total energy of a finite duration continuous signal becomes infinite after sampling
If I have a continuous-time energy signal and multiply it with an impulse train, the frequency domain representation has infinite replicas. The total energy if we sum them up becomes infinite. What ...
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1answer
30 views
Interpreting the cross correlation results
I am new to this forum. I am just trying to understand how to calculate delay (in terms of samples) between two signals using cross-correlation function. I wrote a small Matlab code in order to ...
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0answers
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How to sample along diagonal in 2D FFT
I aquire typically 2D time traces which I process by a 2D Fourier transform. The aquisition is done line by line. First, I let the signal evolve for t1, then an action is performed that possibly ...
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1answer
42 views
Sampling of bandpass signal with bandpass filter
Trying to solve the following problem about bandpass signal sampling.
I have a signal whose Fourier transform is such that $X(w)= 0$ if $w>w_h$ or $w<w_l$.
The reconstruction is done using a ...
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4answers
8k views
Zero, First, Second … nth-order Hold
The rectangular function is defined as:
$$\mathrm{rect}(t) = \begin{cases}
0 & \mbox{if } |t| > \frac{1}{2} \\
\frac{1}{2} & \mbox{if } |t| = \frac{1}{2} \\
1 & \mbox{if } |t| < \...
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1answer
36 views
Frequency response and sampling theorem for triangular function
The triangular function is defined as follows:
$h_l(x) = \begin{cases}1-|x|,&|x|<1;\\0&\text{otherwise}.\end{cases}$
According to ccrma.stanford.edu:
"If the output of the interpolator ...
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1answer
57 views
Zone Plate Reconstruction
I am trying to reconstruct the Zone Plate image and am struggling to remove the last remaining aliasing.
ShaderToy: https://www.shadertoy.com/view/wdGGWK
In the shader above you can see that I am ...
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1answer
56 views
Torque signal fft
I have the following torque signal picked up with a 10.240Hz sampling rate from a testbench.
I am studying its fft which I create on Octave with the following code:
...
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1answer
34 views
Max frequency of cosine in SDR
I would like to transmit a 56 MHz real cosine and receive it using SDR with max complex sample rate equals 61.44MSPS and an analog filter with BW = 56MHz (the transceiver is AD9361). Can I do it? How ...
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1answer
42 views
Impulse Invariant method for digital filter design
One of the known methods for discretizing analog filters is impulse response invariant. We get the impulse response in time domain, discretize it and then get the Z transform.
What I am trying to ...
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1answer
83 views
Find continuous signal given a condition on its samples
Let $x(t)$ be band-limited with $B = \omega_m$. Sampling gives us $$x(nT_s) = \begin{cases}
1, & n = 0 \\
0, & n \not = 0
\end{cases}$$
And $\omega_s = 2\omega_m = \frac{2\pi}{T_s}$. Find ...
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0answers
72 views
Reconstruct $x(t)$ from $y(t)$ and $z(t)$
Let $x(t)$ be band-limited signal with $X(j\omega) = 0$ for $|\omega|\gt \omega_M$. We use $$s(t) = \sum_{k =-\infty}^{+\infty}(-1)^k\delta(t - \frac{kT}{2})$$ for sampling. So we have $z(t) = x(t)s(t)...
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1answer
57 views
Fourier transform of the sampled signal
I want to calculate Fourier transform of the sampled signal in two ways. Let $$s(t) = \sum_{k = -\infty}^{\infty}\delta(t - kT)$$And $z(t) = x(t)s(t)$. So we have $$z(t) = \sum_{k = -\infty}^{\infty}x(...
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1answer
42 views
Build an inverse model for a train of gaussian pulses
I have a stationary signal from a train of Gaussian pulses.
My sampling window is too wide (cannot be reduced). In the example 1 ms. So it is not possible to clearly distinguish one pulse from another....
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3answers
74 views
Meaning of sampling frequency?
Say there is a communication system, which can manage sampling frequency up to 4 MHz (given by software). Can the system be able to process signals with maximum frequency more than 2 MHz? Because ...
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3answers
5k views
How replicas are formed in Frequency domain when a signal is sampled in Time Domain?
I know that sampling in one domian (time or frequency) gives raise to replicas in another domain (frequency / time).
How replicas are formed?
What is this Time domain periodicity and frequency domain ...
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4answers
149 views
What is Frequency Resolution?
Im trying to tackle the following problem while still not having a firm idea on what "frequency resolution" means :
Suppose we sample a continuous time signal with sampling period Ts = 1/2000, and ...
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1answer
78 views
What does the frequency band mean when it comes to finding aliases?
The time signal which i'm trying to find the aliases for is:
$$x:{\mathbb R}\rightarrow {\mathbb R}\\\ x(t)=\cos(50t) +2\cos(70t).$$
If the sample period is $T_s = \frac{\pi}{60}$ then according ...
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1answer
93 views
Sample-rate, filtering, digital-filtering and aliasing
I am strugling with a question that I hope someone can help me with.
I am recording single molecule events which I detect is picoampere square deflections.
I wish to use as gentle low-pass bessel ...
0
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1answer
27 views
Aperture Jitter in Digital to Analog Converters
I have noticed in the literature that there is an internally induced timing jitter inside Analog to digital converters called (aperture jitter). It is caused by the sample-and-hold circuit of the ADC.
...
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1answer
28 views
Sample and Hold Circuit at Digital to Analog Converters
Does DACs contain sample-and-hold circuits? I am a bit confused
thanks
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3answers
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Can we have a Digital Anti Aliasing filter?
I am working on a board that has no antialisaing filter at the input of the ADC. I have option to I implement my own filter using RC + Opamp circuit. But is it also possible to implement Anti ...
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2answers
38 views
Ideal low pass filter output at given sampling frequency
Consider the signal $\cos(30t)$ sampled at $w_s=40 rad/s$ using a unit impulse train. The sampled signal is filtered with an ideal low pass filter with unity gain and cutoff frequency $w_c = 40rad/s$. ...
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1answer
39 views
Recoverable continuous function after average sampling
I have a personal interest in this question, but I don't know if it is unfounded.
Suppose I have a continuous function x (t), which is sampled using an average sliding window, which performs a ...
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0answers
32 views
How should I sample the signal $f(t) = \sin(24t)^3\chi_{[0,0.52]}$ on the interval $[0,1.25]$?
I am from an applied math/PDE background and I don't usually deal with proper sampling and signal processing. I just take roughly what seems to be a good number of samples. But I would like to be ...
1
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1answer
35 views
Oversampling a signal
I’ve built a circuit with an analogue sensor (70 Hz bandwidth) connected to a 24 bit ADC, which is oversampling the signal at 10 kHz. Nyquist sampling theorem implies I should sample by at least 140 ...
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1answer
24 views
Oversample or undersample correlated noise?
I wish to measure nontrivial (non-Gaussian) broadband current noise for its distribution and power spectral density.
The noise is amplified (with transimpedance amplifier) with some characteristic ...
