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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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25Hz low-pass FIR filter for 96kHz high-quality audio

I am evaluating how to implement 25Hz low-pass / 25Hz high-pass filter with flat phase response (i.e. FIR). Apparently straightforward FIR filter would require insane number of taps (>8192) which ...
BarsMonster's user avatar
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Low pass Thiran filter difference equation in Python

I'm attempting to build a time domain low-pass Thiran filter (in Python if that is relevant) based on the original article: https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1083363&tag=...
MGreen's user avatar
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Software based energy meter

I have been implementing a software energy meter. In other words my software has to integrate immediate electrical power over time. The immediate electrical power is calculated based on following ...
Steve's user avatar
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2 votes
5 answers
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Why does the frequency sampling method for FIR filter design operate in this manner?

I'm studying FIR filter design and it's time for the frequency sampling method, my teacher said that to use this method you need to follow the following steps: Sample the periodic frequency response ...
minghierid's user avatar
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Signal recovery is based on the development of the Shannon sampling theorem?

One of the earliest extensions of this theorem was stated by Shannon himself in his 1949 paper, which says that if $x(t)$ and its first $(M - 1)$ derivatives are available, then uniformly spaced ...
Son VuHoang's user avatar
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White noise vs low-pass filters

It seems common that people assume white (aka Gaussian) additive noise. Yet it is also common to use low-pass filters to remove noise. But white noise shows up equally on all frequency bands. So it ...
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Butterworth Bandpass Filter Design

Determine the transfer function for the Butterworth bandpass filter? (At the Transfer Function Factoring and Sp Substitution stage) The Parameter $$a_{pass} = - 1dB$$ $$a_{stop} = - 20dB$$ $$f_{pass1} ...
SKevinAR18's user avatar
3 votes
2 answers
307 views

First order filters in Direct Form I (RBJ Cookbook)

I've implemented second order biquad filters using the famous RBJ Cookbook. I also want to implement first order lowpass and highpass filters. I was hoping to use the same code, so I need to define ...
MysteryPancake's user avatar
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1 answer
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Minimum amount of data needed for low pass filter on real time sensor data

I need to apply a low pass filter up to a period of 10 hours to my data. My sensor has a sampling rate of 1 sample every 5 minutes. I need to know how much data I at least need to have to be allowed ...
TRM's user avatar
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Calculating stopband cut-off frequency and stopband attenuation for FIR lowpass window filter

I am aiming to create a digital windowing FIR filter on MATLAB and have been given specs such as a: sampling frequency of 360Hz maximum filter order of 5 cut-off frequency of 98Hz/ 1.710rad/sample (...
EEE22's user avatar
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Lowpass Filter to Average sinusoid signal

How to get an average of a sinusoidal signal? The frequency of a signal is 50 Hz and could have harmonics, i.e. high THD. I tried to use exponential moving average with low cut-off frequency (about 1....
Rafael Santos's user avatar
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Difference between simple 1st order low-pass filter equations

While reading about 1st order low pass discrete implementations I found out, the following 2 equations achieve similar results, but apparently not identical, but I thought they had the same origin. ...
FELIPE_RIBAS's user avatar
1 vote
1 answer
241 views

Why is there a phasor in the transfer function of an ideal LPF?

I'm learning about Low Pass Filters. My professor said the following is the transfer function of an ideal LPF: $$H_{LPF}(f) = G\Pi\left(\frac{f}{2B_{pass}}\right) e^{-j2\pi ft_0}$$ However, i don't ...
Riccardo's user avatar
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Quasi-static-detector operation principle

Im currently working on a project to get navigation information of a robot from Data-Fusion through different IMUs. First step is to make a calibration and I picked a method where I need to detect ...
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2 answers
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Confusion on when a filter is considered band-pass

As part of an assignment, I was given a filter with a specific set of poles and zeros, namely poles at $0.51 \pm 0.68i$ and zeroes at $1.5$ and $−0.7$. This part of the assignment is titled as "...
Nyquist-er's user avatar
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Matlab FDAtool. Generating integer filter coefficients without gain

I use the FDAtool package to work with digital filters. I have always worked with coefficients in float format. I noticed that FDAtool always makes the b coefficients as integers. It also always adds ...
red15530's user avatar
2 votes
1 answer
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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 ...
ed190's user avatar
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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 ...
Link Coquin's user avatar
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1 answer
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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 ...
Tanmayee Pathre's user avatar
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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 ...
Thoth's user avatar
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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 ...
Emanuel Landeholm's user avatar
1 vote
1 answer
270 views

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 ...
CroCo's user avatar
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2 answers
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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 ...
jpa's user avatar
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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 ...
a name's user avatar
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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 ...
sancholp's user avatar
1 vote
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170 views

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 ...
Teena's user avatar
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1 vote
1 answer
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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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1 answer
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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 ...
Yaz's user avatar
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1 answer
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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 ...
FISqrt's user avatar
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3 votes
1 answer
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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 ...
KJM's user avatar
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2 answers
601 views

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 ...
mabeco's user avatar
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0 answers
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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?
user68373's user avatar
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1 answer
108 views

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 ...
Michael's user avatar
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2 votes
1 answer
128 views

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? ...
BigBrownBear00's user avatar
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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 ...
The Impossible Squish's user avatar
2 votes
0 answers
35 views

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 ...
Rudolf 12345's user avatar
5 votes
2 answers
925 views

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 ...
OverLordGoldDragon's user avatar
1 vote
0 answers
68 views

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-...
Jason Kleban's user avatar
1 vote
1 answer
251 views

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 ...
George kirby's user avatar
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0 answers
128 views

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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5 votes
2 answers
806 views

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: ...
gvg's user avatar
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1 vote
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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 ...
Vojtěch Melda Meluzín's user avatar
1 vote
2 answers
103 views

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 ...
bazz's user avatar
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1 vote
1 answer
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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 ...
S_holmes's user avatar
0 votes
2 answers
116 views

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 ...
sharad gupta's user avatar
3 votes
3 answers
159 views

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 ...
Dan Boschen's user avatar
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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 ...
Mr. Panda's user avatar
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1 vote
1 answer
90 views

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, ...
Levi's user avatar
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