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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group delay of Bessel filters
Wikipedia states that Bessel filters have a group delay within passband of $1/\omega_0$. While the inverse relationship to knee frequency makes sense, it ignores the effect the filter order has on the ...
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I'm struggling to understand the FIR Filter and its application
I'm new to GNU Radio, and I was watching this video However, I didn't quite understand the purpose of the FIR Filter. I know what decimation or downsampling is because I have the book "Digital ...
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Ratio of aliased to desired energy of a sampled signal
In this article "Sampling: What Nyquist Didn't Say, and What to Do About It" from Wescott, the author shows in Figure 6, the plot of the frequency spectrum of a signal which goes through a ...
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Applying Lowpass filter on a signal in time domain gives ringing artifacts - how to get rid of them
EDITED AND UPDATED:
My signal is an impulse response. In the following figure:
The frequency spectrum of the impulse response (original signal) is shown by blue line.
The original signal is ...
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Trying to understand scipy.signal.kaiserord
I am trying to understand scipy.signal.kaiserord example. The example says
We will use the Kaiser window method to design a lowpass FIR filter
for a signal that is sampled at 1000 Hz.
We want at ...
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Theory behind transfer function transforms of the type $H(s) \rightarrow H(f(s))$
My brother wanted me to derive a high-pass version of a Butterworth low-pass filter. I found that the transform $H \left( s \right) \rightarrow H \left( j - j s \right)$ does the thing, but I can't ...
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How to design low pass filter for this case
From control systems perspective, I have two subsystems that are connected in a cascade structure. An outer loop represents a joystick that provides position that runs at 1kHz and an inner loop ...
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Demodulation + LPF gives derivative of modulated signal
I'm new in this community and I hope it is the right place to post my question. Unfortunately, signal processing and electronics in general are not my fields, so I'm sorry if the question is trivial.
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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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Type 1 Chebyshev 3rd Order Lowpass Filter
I'm trying to implement a 3rd order Type 1 Chebyshev digital lowpass filter in C++. I've been having a lot of problems and I'm not sure why. I can plot the transfer function in MATLAB and see that it ...
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Lowpass filter to downsample data
I have some data that is sampled at a certain rate (16384Hz). I am only interested in the 10-30Hz region, so I want to downsample the data. My idea to do this goes as follows:
I apply some kind of ...
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Is lock-in amplifier a correct approach?
I have a noisy signal which is the voltage output from a photodetector circuit. I have researched about extracting signals, and found that lock-in amplifiers are one of the main approaches for the ...
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Lock-in Amplifier: How to improve the output of lock in amplifier?
I tried to extract a pure signal from the noisy signal using a lock-in amplifier with the help of python code.
The output is from a photodetector circuit.
These are the reference signal, expected ...
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Low-pass filtering a clipped signal
In order to downsample a signal sampled at 48KHz, I implemented an anti-aliasing filter. An Elliptic LPF with a cutoff at 16KHz and order of 10. Everything looks OK until the input to this filter is a ...
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In the RMS bandwidth equation, why do we have the energy of the signal in the denominator?
In the following equation:
$$B_{\rm rms}^2 = \frac{\displaystyle\int_{-\infty}^\infty f^2\lvert G(f)\rvert^2df}{\displaystyle\int_{-\infty}^\infty \lvert G(f)\rvert^2df}.$$
It is not clear why do we ...
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Adaptive filtering [duplicate]
I want to mention upfront that I'm not very experienced in this field.
I have a signal $u(k)$ that I get from a black box simulation (sampled irregularly). The signal looks like this:
The blue signal ...
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Low-pass Filter with constant phase response
I would like to design (e.g. in GNU-radio) a low-pass filter where up to the cut-off frequency the phase-response is constant (I do not mean a "linear-phase response"). The rationale is to ...
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Applying filters in the frequency domain
I have data in the frequency domain. How can I apply the low pass filter such that it still removes the high frequency information?
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Demonstrating linear filters on daily weather data
I have daily temperature data from some place on Earth. Apparently, the sampling frequency f_s = 1/day.
I would like to use these data to demonstrate (visually) the use of low-pass, high-pass, and ...
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What are the tradeoffs between shifting a lowpass FIR filter vs using a bandpass FIR filter?
Is there a difference between shifting a lowpass FIR filter to an arbitrary frequency offset versus creating an equivalent bandpass filter, such that the passband and cutoff frequencies are identical? ...
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How to export raw audio from audacity?
Request to Experts:
I am a DSP novice. I would like to experiment with some methods for low pass filtering in the time domain.
To that purpose, I would like to generate a tone in audacity and export ...
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Which audio smoothing algorithm has the lowest latency?
I am working on an audio smoothing project. My inputs are from a record scratching MIDI controller, and I am trying to produce a smooth output (the raw data creates noisy audio).
I'm using a simple ...
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Relation between discrete wavelet transform and filter banks
I have approached wavelet transformation from a projection perspective. Specifically, we can show for a certain class of functions (in the continuous setting) that they can be written in terms of a ...
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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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NUFFT/FFT interpretation
I know this has been covered thousands of times on the internet, but I'm still struggling with it.
My end goal is to cancel out the noise in an Inertial Measurement Unit chip readings so I can double-...
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Why does the discrete bode plot look like the following and if possible explain the black vertical line at the end for an averaging filter
Why in the attached image for a simple 3 point moving average that has been converted into a TF (z domain) is there a wired dip? It seems that when I change the sampling time, the dip shifts to the ...
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Is this how to show decimation in the frequency domain?
Let's say I have a discrete-time signal $y[n]$ that is passed through an Ideal Lowpass Filter (impulse response $h[n]$) to get $y_1[n]$. The filter has cutoff frequencies at $\pm \pi/N$ rad.
Now this $...
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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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Is it possible to lower the slope of a biquad lowpass? [duplicate]
I'd like to implement a lowpass with arbitrary slope. I'm currently cascading biquads in order to get a higher order, hence higher slope. But is it possible to do the opposite - lower the slope of one ...
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Scenarios where Phase Response is (non-)problematic
In order to get a better feel for phase response and how it applies across the field of dsp, I'm looking for example scenarios where a filter's phase response is a concern and where it is not.
Take ...
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Frequency components in Bin averaging
I am back with another question.
Context for the question: I am trying to smooth out the angular velocity data from an encoder. The encoder has 720 ppr and the rough angular speed of the wheel is ...
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Output Precision for Filter
I am designing a low pass filter which takes a 19 bit input.
\begin{align}
\log_2(\max(\mbox{LPF_COEFF})) &= 16.64\\
\log_2(\mbox{sum}(\mbox{LPF_COEFF})) &= 17.87
\end{align}
Now should I take ...
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Subtract Lowpass from Wire to Get Allpass
One technique to make a high pass filter is to subtract a lowpass filter from a wire (meaning subtract the output of the filter from the input as I have demonstrated in this post).
What lowpass can ...
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What parameter to use to decide if accelerometer data are noisy?
I would like to do regression thus I need to know if my input data are noisy.
In this case, I generate accelerometer data [x, y, z] from the sensor.
I have a look ...
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Multiple questions about how to implement practical resampling
I am learning resampling theory, and for the time being I am specifically interested in downsampling. I have a textbook that is not a dsp textbook but has a section on resampling. The way they put it, ...
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"There's no ideal lowpass filter" - really?
Sinc is $\propto 1/t$. If $x(t)$ is bounded, then there exists $t: |x(t)/t| < \epsilon_M$, where $\epsilon_M$ is machine epsilon. If $x(t)$ is also time-limited, it also means there's $\tau$ such ...
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transformation methods for digital filters
i have the following question:
in digital filter design what's the difference between the methods of transformations :
bilinear vs impulse invariance vs Euler vs step invariance.
thank you!
Here is a ...
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FIR Filter for complex float
I have been using FIR filters for float variables, can I know how can I pass complex float variables ( complex float buf[1024] ) to the filter equations? I mean pointers to the variables of type ...
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How we determine type of filter with pole(s), zero(s)? [duplicate]
Let's say we have this Laplace transform:
$$H_{1}(s)=\frac{1}{(s+1)(s+3)}\;, \; \Re{e} (s)>-1 $$
So, we know that there is a poles at $s=-1$ and $s=-3$.
With these informations, we found that to be ...
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Phase vocoder has crackling artifact
I built a phase vocoder in JavaScript based on this paper. It works great, except for a crackling artifact that is present in the rebuilt signal.
I recorded this clip if you want to hear what it ...
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LTI Filter for DAC Reconstruction
$\textbf{Question:}$ An analog-to-discrete is designed as,
$$x[n] = x_a(nT)$$
In an attempt to recover the analog signal from its samples x[n], a D/A converter is designed as ,
where $x_1(t)$ is ...
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What does frequency filtering actually practically mean?
I've got an electronics circuit which was filtering between a Passive HPF stage (1uF and 330K) and an Active LPF stage (4.7uF and 10K). As you can see it was filtering between 0.48Hz and 3.38Hz, and ...
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Trying to implement a digital LPF
So I took this digital LPF from some website:
And tried implement it first in MatLab to see how it goes, here's the code used:
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Why the sum of filter coefficients of an FIR filter does not add to 1?
In MATLAB, I have generated an FIR low pass and high pass filter of order 16. The code is as follows:
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Is f/fL a high pass filter where fL is a low-pass version of f?
Let there be a signal f and its low pass filtered signal be fL. Then what can we say about the spectrum of f/fL ?
To be specific I am obtaining fL simply using gaussian blurring in the spatial domain.
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Why are moving average filters and integrators considered low pass filters?
Why are digital moving average filters and integrators considered low pass filters in baseband signal processing applications?
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Intuition for how much ringing a particular filter will induce
I've seen figures in various books about the the tradeoff between aliasing and blurring when using a gaussian-like filter: the narrower it is, the more it cuts off low frequencies and thus blurs it, ...
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Why is LPF amplifies the baseband signal?
I am working with a PDM digital microphone and I've sampled the data using a FPGA.
For the beginning I am working in python to do all the algorithm, then I will implement it in FPGA.
I am using two ...
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Derivation of a non-ideal low-pass rectangular windowed FIR filter
I have been trying to understand certain aspects of FIR filter design which have frankly annoyed me for some time such as exactly why the critical frequency $\omega_c$ in a low-pass FIR filter is ...
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Why couldn't I reapply a LPF to remove more noise?
I have a piece of raw accelerometer data consisted of 10,000 samples to be processed offline. Since the movement or rotation of the object is moderately slow and smooth, I would think that I can ...
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