Questions tagged [sampling]

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

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1k views

What is the opposite of sampling called?

We call the conversion from a continuous time signal $f(t)$ to a discrete time signal $f_s[k]$ "sampling". Is there a name for the reverse operation, i.e. creating a continuous time signal from a ...
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546 views

minimum sampling rate for very short duration signals

I understand that sampling rate should be twice the signal bandwidth for successful reconstruction. But what I don't get is how this translates in the time domain. For example, I have a sine wave ...
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672 views

Regarding the Nyquist Criterion

I recently read that with compressive Sensing it possible to sample the signal at a rate lesser than that suggested by Nyquist Criterion. However, I am still not getting how this is possible. Can ...
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1answer
920 views

FFT and aliasing

I have got a txt file which contains voltage and time data. When I did fourier transform using fft function in matlab I got complex numbers. I understand that the real part is the magnitude and the ...
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108 views

About sampling and wireless networks

Wireless networks operate on a high frequency, say some several gigahertz. Are the signals really sampled at that high frequencies? If I got it correctly there's some modulating/demodulating in signal ...
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Offset effect in FFT magnitude

i will use matlab code just for convenience, i get the same behavior using a C++ code. I have two signals: ...
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522 views

Where can I find an authoritative (peer-reviewed or textbook) reference to sampling-induced beating?

I presume we are all here well aware about foldback aliasing when sampling signals above the Nyquist frequency; i.e. half the sampling rate. By contrast, the phenomenon of beating occurs when ...
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12 bit ADC to 8 bit DAC

A bit of background information: I plan to start experimenting with digital signal processing on microcontrollers. The particular microcontroller I plan to use (TI Stellaris LM4F230H5QR, from the ...
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1answer
161 views

What is the optimal adaptive grid for calculating a DFT using a fixed number of sampling points?

I'm currently facing the following problem: I want to approximate the Fourier transform $F(\omega)$ of a (let's say, $L^2(\mathbb R)$) function $f(x)$ by calculating the discrete Fourier transform, ...
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246 views

How does Delta-Sigma Modulation convert a 1-bit signal to higher resolution signal?

I've looked at various resources about Delta-Sigma modulators, and I find them fascinating. However, I'm confused on a particular point and and am looking for an explanation. In my understanding, ...
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1answer
348 views

Slow sampling of signal and averaging over n periods

Can one in theory achieve as high accuracy as needed by sampling a sinusoidal signal over n Periods? Is there a formula that connects the signal frequency (f), sampling frequency (fs), periods (P) and ...
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394 views

Sampling at subnyqvist frequencies

I went through this material on Sampling theorem. http://www.wescottdesign.com/articles/Sampling/sampling.html It uses a powerline signal example and concludes that if a signal is cyclic and ...
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3answers
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How to pick coefficients for Fractional Delay Filters?

I have a Virtex 6 FPGA running at 200MHz with ADC/DACs on it. I have been converting a WiFi signal (2462MHz) down to a more reasonable IF of 25MHz, sampling, running the signal through taps, tweaking ...
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378 views

Practical wideband digital beamforming for large arrays in radar applications

I do understand the mathematics behind digital beamforming but I am not sure how such systems are practically implemented. For example, in a typical wideband FMCW radar operating in S-band, the (...
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1k views

Sampling Frequency Math

The Nyquist formula for digitally sampling and recovering a continuous waveform is well known. Are there any mathematical formulas that show that it is computationally infeasible (or impossible) to ...
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816 views

Sampling the Dirac function

I would like to ask a theoretical question concerning the Dirac function. The Fourier Transform of the Dirac function is the value 1 (DC) for every frequency. If we consider the Sampling Theorem, we ...
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453 views

What is the most computationally efficient way to generate 100 sine waves layered on top of each other?

Right now I simply do this (pseudocode) for freq in freqs: for i in len(samples): samples[i] += sin(...) Is there a better way? This is for ...
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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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1answer
3k views

Spectrum of a Signal Going Through a Zero Order Hold Sampling System

What does the spectrum of a sampled signal look like if one uses a zero-order-hold? There is some information in: Sampling theorem and Dirac comb, but I am wondering, how to apply this in practice. ...
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73 views

Getting error in fit

I was wondering if anyone had run into the problem of trying to estimate errors in their signal processing on spectroscopic data. I know that many people use spectroscopic techniques to estimate ...
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Need for Oversampling in OFDM and symbol time determination

I am trying to implement OFDM on gnuradio. I have two questions. The sampling frequency which is slightly higher than available bandwidth satisfies Nyqvist criterion for complex baseband signals. So ...
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1answer
262 views

Explanation of LidarBoost Algorithm?

I am trying to understand the LidarBoost algorithm as explained in this paper (PDF warning). I don't understand how they take the original depth-images $Y_k$ and transform them into the up-sampled ...
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3answers
936 views

Determining the mean of of a sampled signal (improvements to time averaging method)

I am sampling a signal at 1kHz, which is essentially a single-frequency sinusoid with a DC offset (and a small amount of noise). I don't know the precise frequency of the sinusoid (it is at most 10Hz),...
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1answer
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Determining sampling rate in OFDM demodulation

I have seen that in OFDM, the sampling rate is much lesser than twice the bandwidth of signal. why is it so? How is sampling rate calculated in OFDM? Does it depend on the modulation type used inside ...
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1answer
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Relation between CTFT and DTFT

I need to transform this function: $$ x(t) = 4\sin(20\pi t ) - 5\cos(24\pi t ) + 3\sin(120\pi t ) $$ into a sequence $x(n)$ given that the sampling frequency should be 50 Hz. So that means the ...
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208 views

Ways to analyze electrical signals without FFT?

I am collecting a 15Hz sine wave at 1500Hz. Therefore, every 100 points of data collected should contain a single complete sine wave. If I sample for 10 seconds, I will have 15000 points of data. If ...
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743 views

How to measure the agreement between to curves?

I have values (plotted below) of expected RSSI values over time that I would like to compare with my measured RSSI values. What I was looking for was a way to quantify it so I can change parameters ...
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1answer
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Dynamically changing cut-off and sampling frequency of a digital filter

I have designed a low pass filter that smooths the output coming from an accelerometer attached to a vibrating machine. I designed this assuming cut-off frequency $f_{c1}$, and sampling frequency $f_s$...
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BandPass Signal Vs PassBand Signal

Am reading Rick Lyons - Understanding DSP book about Sampling. I have few doubts related to this chapter. what is the difference between Bandpass Signal and a Passband Signal ? Can somebody give an ...
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127 views

Instantaneous Frequency variation

I am looking for a method to calculate the instantaneous pitch variation within a speech signal for time-warping application. Sample by sample frequency variation knowledge within a frame will give ...
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1answer
184 views

simulating multipath via tap delays in FPGA

I have a Xilinx FPGA running at 200MHz with an ADC and DAC on board. I am taking a 2462MHz sine wave (pretending it is 802.11b chan 11), mixing it down to 40MHz putting it through my FPGA, mixing it ...
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2answers
13k views

Adding echo to audio sample

I have recorded my own voice in Matlab and I intend to add some echo to it.I came up with one solution for getting the desired echo effect: Delay the sampled audio in the time domain and adding it to ...
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2answers
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How to predict the spectrum of an aliased/folded signal without looking at the FFT?

This seems like a trivial concept but I just can't get the hold of it. I have a signal with two complex sinusoids having frequencies -25MHz and 17MHz. Currently it is being sampled at 64MHz so I get ...
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Converting frequency from $\textrm{Hz}$ to radians-per-sample

In MATLAB I have to pass cut-off frequency for designing a filter. But this Cut-off frequency is in radians-per-sample. How do I convert my analog Cut off frequency in $\textrm{Hz}$, into the required ...
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53 views

How to calculate the quantum of the difference between two value of clock counter where the values are divided by 64?

I have a counter in my embedded system with f = 64 Mhz. let's say its read value is $cnt_i$ where $i$ is the index of the time I sampled it. $$\Delta = cnt_{i+1} -...
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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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1answer
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pitch vs playback rate

Let's say I have an audio sample, whose pitch is known to be C4 (don't wanna go in detail here, let's say I just sampled a tuned piano playing the C4 key). The rules of the game are: I can only ...
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115 views

Voice sample prediction scheme

I have some telephone voice audio with occasional "blips" in the audio. The blips appear to come from an IP link buried in the PSTN (this is a conceptual explanation, so don't worry about things like ...
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Trying to understand whether digital signals help in better bandwidth utilisation or not

Suppose x(t) is a continuous-time signal and x(n) is a discrete time signal obtained by sampling the signal x(t) at a Nyquest sampling frequency Fs. The signal x(t) requires a bandwidth of B1 Hz for ...
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2answers
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Sampling a Unit step function

I have following two related questions concerning unit step function. 1-I want to sample the following signal. What will be the sample value at t=0? The signal takes 0 time to change from 0 to 1. So ...
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2answers
7k views

what is the effect of variation of duty cycle of sampling frequency on a reconstructed signal

I have been asked to study an experiment which says "what is the effect of variation of duty cycle of sampling frequency on a reconstructed signal" I am not an electronics/electrical engineer I am ...
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1answer
171 views

reduce harmonics produced by microcontroller

I'm generating an 18kHz sine signal using a dsPIC microcontroller at 44100kHz (I'm not sure I can call it sampling rate, maybe generation rate, although the concept is the same). The dsPIC's DAC then ...
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3answers
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best window for close frequency components

I'm currently designing a receiver which has to determine whether a signal contains specific frequencies or not. The frequencies are at constant 215Hz difference: ...
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1answer
3k views

Why is oversampling helpful to an anti-alias filter?

Why does oversampling make the job of an anti-alias filter easier? I don't understand the intuition on why it becomes helpful. Isn't it economical to just keep the sampling rate at the minimal level,...
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1answer
717 views

How do I resample an image to a rotated grid?

I have an image, I, sampled on a uniform grid: $\ x_i = i*\Delta x, y_j = j*\Delta y, $ I need to resample this image to a grid rotated counterclockwise by an angle $\ \theta$ around $\ (x_0,y_0)$: ...
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1answer
222 views

Locking on to a square wave signal with minimum oversampling

I'm designing a device that will have an IR photodiode connected to a low power microcontroller's ADC pin. At times, another device will be transmitting a 48KHz square wave, and I'd like to be able to ...
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2answers
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Matlab BOC (binary offset carrier)

I am trying to implement a binary offset carrier (BOC) direct sequence spread spectrum scheme in MATLAB. In that scheme, a code $c(t)$ (a binary vector which repeats after a certain number of zeros ...
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1answer
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Sampling of a continuous function: Kronecker's or Dirac's delta?

I've been reading some papers in signal proccesing and I'm very confused about the issue in the title of my question. Consider a continuous function of time $t$, $f(t)$, that I sample at uneven times $...
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4answers
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How does the quantization error generate noise?

I'm learning about sampling and DSP on my own. I have a hard time to understand how the quantization error results in noise. I think I miss a fundamental understanding but can't tell what it is. So ...
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764 views

determine two signals with a scale factor

Suppose I have 2 signals from function $f_1(x)$ and $f_2(x)$, respectively, and assume the sampling rate is above Nyquist frequency, so we can restore the underlying functions $f_1(x)$ and $f_2(x)$. ...