In signal processing, sampling is the reduction of a continuous signal to a discrete signal.
6
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2answers
63 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 ...
0
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3answers
53 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 ...
5
votes
3answers
228 views
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 ...
2
votes
1answer
100 views
Spectrum of a zero-order-hold signal
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.
...
4
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0answers
32 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 ...
0
votes
1answer
55 views
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. ...
3
votes
1answer
82 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 ...
5
votes
3answers
123 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 ...
0
votes
1answer
66 views
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 ...
2
votes
1answer
52 views
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 ...
1
vote
2answers
69 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 ...
5
votes
1answer
97 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 ...
4
votes
1answer
74 views
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 ...
1
vote
3answers
108 views
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 ...
2
votes
0answers
40 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 ...
0
votes
1answer
61 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 ...
1
vote
2answers
203 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 ...
2
votes
2answers
113 views
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 ...
2
votes
1answer
110 views
Converting frequency from 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 Hz, into the required ...
0
votes
1answer
40 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} ...
1
vote
2answers
106 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 ...
3
votes
1answer
59 views
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 ...
2
votes
0answers
59 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 ...
0
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0answers
52 views
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 ...
1
vote
2answers
98 views
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 ...
0
votes
2answers
148 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 ...
1
vote
1answer
56 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 ...
2
votes
3answers
141 views
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:
...
4
votes
1answer
166 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 ...
4
votes
1answer
104 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)$:
...
0
votes
1answer
185 views
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 ...
10
votes
1answer
484 views
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 ...
7
votes
3answers
444 views
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 ...
5
votes
2answers
100 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)$. ...
7
votes
2answers
234 views
Is there such a thing as band-limited non-linear distortion?
So if you generate a square wave by just switching a signal between two values, at sample boundaries, it produces an infinite series of harmonics, which alias and produce tones below your fundamental, ...
3
votes
2answers
672 views
Alias frequency Formula
I'm taking a multimedia systems class in my MSc Computer Science, and I'm having some trouble understanding the formula for the alias frequency - this could stem from my misunderstanding of the alias ...
3
votes
2answers
130 views
If sampling rate is high does that increase the error or decrease the error?
Suppose we are tracking a computer mouse on the screen, if we increase the frequency of the sampling rate(to very high values) then would that increase the error in getting the exact position of the ...
8
votes
1answer
281 views
Directly compare subpixel shifts between two spectra — and get believable errors
I have two spectra of the same astronomical object. The essential question is this: How can I calculate the relative shift between these spectra and get an accurate error on that shift?
Some more ...
4
votes
3answers
1k views
Demonstrating the effect of aliasing
How does the signal look when we don't use the Nyquist rate to remove aliasing from a signal during sampling?
Let's suppose the signal is sinusoidal, with a frequency of 500 Hz and an amplitude ...
4
votes
1answer
334 views
What is “Equivalent Time Sampling” and what is it good/used for?
The literature on this method seems scarce, but I know that it has been used on radar systems to 'get away with' not having to sample nearly as fast as Nyquist would otherwise dictate, (at the cost of ...
4
votes
1answer
60 views
What is the difference between the Point Spread Function and Sampling Aperture?
I've been told that the point spread function of a pixel is its distribution of intensity, while the sampling aperture of a pixel is its distribution of sensitivity. I'm a little unsure of what the ...
4
votes
1answer
179 views
Reference for Supersampling
I want to downsample images to arbitrary sizes using supersampling to avoid aliasing effect.
The only two good explanations I found were on Wikipedia and everything2.com, but there are still gaps. ...
4
votes
2answers
86 views
Compensating for measurement errors
I have a system where I sample some data periodically (every 10usec). The shape of the data is triangle, in other words it linearly increases and decreases in time. (Both theory and practice are in ...
6
votes
2answers
227 views
The current state of the art in audio signal interpolation
Three questions:
1) what are all the metrics one can use to measure audio interpolation quality, objectively (but also in terms of psychoacoustics if possible)
2) by those metrics, what is the ...
13
votes
1answer
864 views
“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 ...
4
votes
1answer
703 views
How to determine where to sample for demodulation of BPSK signals?
I have a simple BPSK demodulator. Very simply, the signal comes in and is split into two branches, one for I and one for Q.
The I branch is mixed with a sin wave of the carrier, and the Q branch ...
5
votes
2answers
188 views
Is there any way to make a sampling rate reduction in the frequency domain?
Is there any way to take advantage of the frequency domain to make a clean/nice sampling rate reduction effect ? and how ?
Basically, deducted from my tests:
if I set to 0 the magnitude uppon a ...
7
votes
3answers
716 views
What is anti-alias pre-filter for preventing aliasing after under-sampling?
We know that the under-sampling results in aliasing and frequencies higher than half of the Nyquist rate is not distinguishable. I've a base band signal that I want to use the higher frequencies which ...
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votes
1answer
91 views
What is the smallest sampling points that can recover the signal?
Propose that we have a signal with a model of
$$
f_{4at0} = v_0(1 - \epsilon + \epsilon \exp(-c_l(t_{t2d}-t_0)))
$$
$f_{4at0}$ is dependent variable while $t_{t2d}$is independent variable,others ...
6
votes
3answers
269 views
What is the effect of aliasing on the magnitude of the autocorrelation?
I've a question about the effect of aliasing on the magnitude of autocorrelations. From a simulation in MATLAB, I don't see any effect of aliasing or any need to anti-alias filter when I take the ...
