Questions tagged [lowpass-filter]
A low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency.
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low pass filter and FFT for beginners with Python
I am new to signal processing and especially to FFT, hence I am not sure if I am doing the correct thing here and I am a bit confused with the result.
I have a discrete real function (measurement ...
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What is the physical interpretation of Lowpass/Highpass filtering?
In Image/Signal processing context we have seen/we know that if there are say 4 samples and if we take an average of those 4 samples, then we say that the result sample is a low pass filtered output ...
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How can I lowpass filter by only reducing peak data?
I have a 2D image, which I want to lowpass filter, with these constraints / quality metrics:
I can not "add" light to the image, so each pixel in the result
should be <= the corresponding pixel in ...
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How to write lowpass filter for sampled signal in Python?
I have some signal that sampled each 1 ns (1e-9 sec) and have, let say, 1e4 points. I need to filter high frequencies from this signal. Let say I need to filter frequencies higher than 10 MHz. I want ...
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Differences between filtering and polynomial regression smoothing?
What are the differences between classical low-pass filtering (with an IIR or FIR), and "smoothing" by localized Nth degree polynomial regression and/or interpolation (in the case of upsampling), ...
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Why is $y(n) = x(n) + x(n-1)$ a low pass filter?
I have found that this is a simple, but bad lowpass filter:
$$y(n) = x(n) + x(n-1)$$
However, I can't understand why it is a lowpass filter. What is its cutoff frequency?
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Is a high-passed signal the same as a signal minus a low-passed signal?
My question is, if I want to high-pass a signal, is it the same as low-passing a signal and subtracting it from the signal? Is it theoretically the same? Is it practically the same?
I have searched (...
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Documentation about filters in general
I already posted this question on StackOverflow. I got a suggestion to go for a better answer here.
To make the question more concise I'm interested in an introduction to digital filters, any ...
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Why would one use a Hann or Bartlett window?
Suppose we're designing a low-pass FIR filter, and I want to use one of these three windows: Bartlett, Hann or Hamming. From Oppenheim & Schafer's Discrete-Time Signal Processing, 2nd Ed, p. 471:}
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Savitzky–Golay filter vs. IIR or FIR linear filter
A traditional IIR / FIR filter (lowpass to remove the high freq oscillations), e.g. moving average,
or a Savitzky-Golay filter
can all be useful to smoothen a signal, such as an envelope signal:
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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,
$$
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Apply Low pass Butterworth filter in Python
I want to use a low pass Butterworth filter on my data but on applying the filter I don't get the intended signal. Here is the dummy code:
Signal A:
...
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How should a moving average handle missing data points?
I'm writing a program that averages the user's weight across different days. I'm planning to use a 5-point moving-average (current day, two before and two after). Sometimes, a data point is missing ...
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Savitzky-Golay filter parameters
I am trying to smooth a series of data in order to obtain a continuous function that could represent that given data set.
It came out that the Savitzky-Golay method could be a good way.
Now, I don't ...
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First order low pass filter
I am trying to better understand the first-order low pass filter:
Summary:
Per wikipedia, a first order low pass filter yields the following in discrete time:
$$
\frac{Y(s)}{U(s)}= \frac{\omega_{c}}...
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Exponential moving average cut-off frequency
I am trying to implement a low pass filter from this example.
What is the cut-off frequency for this type of filter? Is it $$F_s \left(\frac{1-\alpha}{2\pi\alpha}\right)$$ where $F_s$ is sampling ...
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Filtering of streaming audio
Given something like 103 data points ($N=103$), a DFT will give back 103 frequency values. Then to do something like filtering the high frequencies involves setting the high frequency values from the ...
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What is the name of a low-pass filter that tracks rate of change?
When applying a low-pass filter to a constantly changing signal, there will be a lag between the actual value and the filtered value. For example, if f(x) = x, the ...
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What is this sinc doing in my LP-turned-HP filter output?
I'm trying to HP-filter a signal by LP-filtering it and subtracting the output from the original filter. To obtain the LP-filtered signal, I backward-forward filtered using a third-order Butterworth ...
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Where do RBJ's analog shelving filters come from?
In RBJ's Audio EQ Cookbook, the analog prototype for a low shelf filter is given as such:
$$H(s)=A\cdot\frac{s^2+\left(\frac{\sqrt{A}}{Q}\right)\cdot s + A}{A\cdot s^2 + \left(\frac{\sqrt{A}}{Q}\right)...
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How does a low-pass filter programmatically work?
I have been working on a simple low pass filter for < 100 Hz metering in my application. But so far, I am struggling with the theory behind it all. It's cool that I got it working, but I'd really ...
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Low pass filtering on short int (16 bit PCM) samples
I am writing software for processing audio given as 16-bit PCM samples. The first stage of the processing involves calculating the energy (or total variation) in a certain frequency range (above a ...
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complementary IIR filters
I would like a pair of complementary IIR filters (lowpass/highpass). By complementary, I mean, when the output from the two filters is summed, the original signal is recovered. I thought I could build ...
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2-d circularly symmetric low-pass filter
For a square pixel grid, the ideal 2-d low-pass filter with a horizontal and a vertical cut-off angular frequency $\omega_c$ in radians has an impulse response (kernel) $h_{\small\square}(x, y)$ that ...
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How to smooth a signal?
The easiest way to smooth a signal is by moving window average.
A more advanced way is to use a Savitzky-Golay filter.
From wikipedia:
The main advantage of this approach is that it tends to ...
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Filter message from noisy voice signal
I am trying to decipher a message hidden within a very noisy audio file(.wav)(I think it is white noise with an additional low drone). The message is a six digit number. I have not have any further ...
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Single-pole IIR low-pass filter - which is the correct formula for the decay coefficient?
A single-pole IIR low-pass filter can be defined in discrete time as y += a * (x - y), where y is the output sample, ...
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Can you turn a square wave into a sine wave using a low pass filter?
And if it could, would it make the sound of the square wave thinner than before because of losing its harmonics?
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What are the advantages and disadvantages of Kalman filter compared with FIR, IIR and low pass filter to filter data with noise?
It is known that the Kalman filter can filter the data with noise. I also find it works well after using it compared with FIR, low pass filter,etc. Now, I have a couple of questions about the ...
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Why is the median filter called 'edge-preserving'?
I want to know about median filtering. Recently, I read that it is best for preserving edges. But how does it preserve edges?
I need complete knowledge of median filters. Why it is non-linear filter ...
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FIR vs IIR filter
In my filter design, FIR gives order 14 and IIR gives order 8 or 4.
so what are the disadvantages of IIR design?
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How is the lowpass to bandpass transformation derived?
I'm using a lowpass to bandpass filter transformation:
$$ s \leftarrow Q \left( \frac{s}{\omega_0} + \frac{\omega_0}{s} \right) $$
Based on the wiki article: http://en.wikipedia.org/wiki/...
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Choice of Gaussian kernel parameters when lowpass filtering before image resampling?
I need to decimate a signal by a factor of q.
More specifically my signal is a 3D "image": $\ I(x_i,y_j,z_k)$,
which I need to downsample by a factor of two in the z direction.
I want to do lowpass ...
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Low pass filter algorithm origin
I have been doing some research, because I used this algorithm that's very spread in the web:
y += a * (x - y)
or
...
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Simple software low pass filter
I am measuring voltages and currents of a 3-phase electrical machine and I need to calculate the power. Every interrupt (frequency between 30-70kHz) I get values (voltages, currents) from analogue-...
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Using a low pass filter to interpolate signal
In my DSP university textbook, the interpolation process is described as follows:
In order to represent a baseband signal $x[k]$ at an increased sampling rate with the same shapes of its time-...
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Using oversampling to increase resolution of a DC-signal as input
Currently I'm working on a project which uses oversampling to increase the resolution of a 12 bit ADC to a maximum of 16 bits. My goal is to fully understand the theory behind oversampling and why it ...
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What exactly is Savitzky-Golay differentiation filter?
I could understand Savitzky-Golay filter as being smoothing filter, but then there also seems to be Savitzky-Golay differentiation filter, though for some reason, details do not seem to be clear.
So ...
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How to estimate taps required for Parks-McClellan filters
I have some code based on Jake Janovetz's Parks-McClellan (Remez) filter generating code. How can I estimate the number of taps required to build a lowpass filter given requirements for pass band ...
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Discrete Time Fourier Transform (DTFT) for an unstable system (Ideal Low Pass Filter)
The Dirchlet conditions state that if the signal is absolutely summable then it the DTFT of the signal definitely exists. This is a sufficient condition but not necessary condition.
There are ...
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Removing values from FFT result same as filtering?
I don't quite understand why the textbooks say it is impossible to implement an ideal low pass filter.
If I was to take the FFT of a discrete signal x[n], with Matlab's fft function I'd be returned ...
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Why is implementing a digital LPF with low cutoff frequency but high sampling frequency infeasible?
I am new to signal processing and I want to implement an LPF using SciPy. In order to do so, I used the following python code from: here
The code itself looks like:
...
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What is the name of this digital low pass filter?
I found this digital filter in code I am working on. It is a low pass filter. In the code it is called an "alpha filter", but it is not the same as the alpha filter mentioned here.
I post the ...
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Difference Between Equiripple & Least Squares Design for FIR Digital Filters
For an efficient and optimized digital FIR filter design, there are two methods available broadly, Equiripple filter design & Least Squares filter design. A general method for designing a filter ...
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Low pass fir filter with non-unity gain
In my filter specs, the passband gain is given as 6.02db. How do I achieve this?
Usually all texts give the passband gain as 0db (as well as passband ripples if any).
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What are the characteristics of a "good" smoothing convolution kernel?
At work we were smoothing a signal by convolving with either
f1=[0.2000 0.2000 0.2000 0.2000 0.2000]
or
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Shannon interpolation formula for downsampled data with an "almost ideal" low pass filter
Let $x[n]$ be a discrete time signal with DFT given by $X(f)=\sum_n x[n]e^{-2\pi inf}$ supported on $[-1/2M,1/2M]$ with $f\in[-1/2,1/2]$.
I can then down-sample to get $y[n]:=x[nM]$. Then, let
$$\...
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Fast Integer 8 Hz 2nd Order LP for Microcontroller
I need an 8 Hz 2nd order LP filter. It does not have to be terribly accurate but it should be 2nd order-ish. Performance is much more important.
My sample rate at the moment is ~9.5 kHz. The filter ...
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How to measure aliasing?
Aliasing is bad, and we want good filters when downsampling. While what qualifies as aliasing is well-defined mathematically, and we can manually design filters with various tradeoffs, how do we ...
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Derivation of the lowpass to bandpass transformation
I have a basic question.
The "well known" lowpass to bandpass transformation is
$$
s \longmapsto \frac{\bar{s}^2 + \omega_1\omega_2}{\bar{s}(\omega_1 - \omega_2)},
$$
which gives a bandpass ...
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