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1500 questions
11
votes
5 answers
Why is Scipy implementation of Hilbert() function different from Matlab implementation of the function?
I am trying to fit Hilbert envelop to a high frequency ultrasonic signal of frequency 250 KHZ and sampling rate 12000000. Raw signal looks like below: .
I used hilbert() function from scipy.signal package in python this is what it looks like .
The…
Spandyie
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11
votes
1 answer
Python's $\tt resample$ vs $\tt resample\_poly$ vs $\tt decimate$
I have multiple signals each measured with a sampling rate 300Hz. They are mostly periodic, although there are some parts of some of the signals, that seem to be random and do not follow the rest of the pattern(could be noise). I want to downsample…
Andreas G.
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11
votes
3 answers
First order low pass filter
I am trying to better understand the first-order low pass filter:
Summary:
Per wikipedia, a first order low pass filter yields the following in discrete time:
$$
\frac{Y(s)}{U(s)}= \frac{\omega_{c}}{s+\omega_{c}}
$$
yields
$$
y[k] =…
kando
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11
votes
3 answers
What is the Fourier Transform of a constant signal?
I am trying to figure out what the fourier transform of a constant signal is and for some reason i am coming to the conclusion that the answer is 1. Or better yet a step function.
Micheal C.
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11
votes
1 answer
How Can I Use MATLAB to Solve a Total Variation Denoising / Deblurring Problem?
The Total Variation Denoising Problem is given by:
$$ \arg \min_{x} \frac{1}{2} {\left\| A x - y \right\|}_{2}^{2} + \lambda \operatorname{TV} \left( x \right) $$
Where $ \operatorname{TV} \left( \cdot \right) $ is the Total Variation Norm.
How…
CEB12
11
votes
2 answers
Effect of windowing on noise
I understand that truncating a signal in time 'smears' the frequency response depending on the window chosen. In general, the shorter the signal duration, the more 'flattened' the frequency response, as seen in The Fourier Transform of the Box…
abc
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11
votes
1 answer
When is cubic spline interpolation better than an interpolating polynomial?
The following plot is a slight variation of an example in a text book. The author used this example to illustrate that an interpolating polynomial over equally spaced samples has large oscillations near the ends of the interpolating interval. Of…
Ted Ersek
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11
votes
4 answers
Peak Signal to Noise Ratio (PSNR) in Python for an Image
How do I calculate the maximum signal to noise ratio (PSNR) in Python? Is there any library that can calculate PSNR for Image?
Sudip Das
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11
votes
5 answers
Mathematical question that comes out of using bilinear transform
So this is related to the Cookbook and I tried solving it maybe two decades ago, gave up, and was reminded of the unsolved problem. But it's pretty damn straight forward, but I still got slogged down in the muck.
This is a simple Bandpass filter…
robert bristow-johnson
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11
votes
3 answers
How to check the FFT results of a sine wave?
I have been given an audio file (sine wave) 1000Hz as an input to my FFT algorithm.
I have got 8192 power spectrum samples in a array.
What is the best and easiest way to check whether my output is right or wrong?
If I give a silent audio file then…
Warrior
11
votes
4 answers
Whittaker-Shannon ($\mathrm{sinc}$) interpolation for a finite number of samples
Given an infinite number of samples $(N)$, a higher (or lower) number of samples $(cN)$ can be derived using sinc interpolation followed by sampling. How can this be applied to finite length signals?
With $\mathrm{sinc}$ interpolation, one can…
Television
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11
votes
2 answers
Frequency shifting of a quadrature mixed signal
I've a quadrature mixed signal with 10 MHz as highest frequency available. I want to shift it to any frequency lesser than 10 MHz. I should get it by multiplying this signal by cosine of the required frequency. Right?
Sumbul
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11
votes
2 answers
Transfer function of second order notch filter
Can anyone mention the transfer function of second order notch filter to remove the line frequency of 50 Hz, in terms of frequency and sampling rate.
Just like for Low pass Butterworth filter as,
$$
H=…
Sudharshan
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11
votes
1 answer
how to detect center of a blurry circle with opencv
I have got the following image:
There are curvs on the picture. i would like to find center of the circles containing curves.
i tried opencv and hough circle transform but had no results.
JingKe
- 111
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11
votes
1 answer
How does OpenCV find chessboard corners?
What are the internal workings of the OpenCV function findChessboardCorners?
Geerten
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