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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How do I set this two pole filter to dynamically update frequency

I am trying to build a filter modulator that dynamically updates a low-pass filter's cutoff using a low frequency sine wave that gets its cutoff frequency updated often. It works like a tremulant but ...
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Bio-signal discontinuity after FIR filtering

I'm filtering respiration signal. I have a signal of duration equal to 10 minutes, so I decided to divided it into period of 10 s. I filtered each epoch with FIR filter, but I have discontinuities ...
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How to solve this question on SSB modulation? [closed]

A message signal $m(t)$ has components at frequencies of 100, 200, and 400 Hz. It is SSB-modulated on a carrier with $f_c = 100 kHz$. The resulting passband signal $u_p(t)$ is demodulated by first ...
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LPF in the stage of IQ demodulator is it a analgor filter or digital filter?

I recently designed the LPF of the IQ demodulator using the Butterworth LPF refering to https://dspillustrations.com/pages/posts/misc/baseband-up-and-downconversion-and-iq-modulation.html. But I have ...
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How to choose median filter width?

In my signal processing pipeline, I normally expect data sampled at 100Hz, on which I then apply a median filter of width 10. My question is: How should I change the width for data sampled at ...
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Digital Audio Amplifiers

Can anyone tell me why a filter that blocks DC signal in an Amplifier would have a cutoff frequency of 4 Hz . Why would someone choose a frequency as low as 4Hz to filter out DC content before ...
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Get the transfer function when using the “designfilt” command in MATLAB

To put things into perspective, I initially had these four graphs in MATLAB, whose data were sampled with a rate of 10 samples/sec :- I wanted to remove some of the spikes on the blue graphs, so I ...
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Should we use a digital low pass or high pass filter to remove sensor bias?

Consider a continuous signal oversampled at, say $2 \;kHz$, and then system digital low pass filtered to a $100\;Hz$ frequency which is the control loop frequency. It is known that there is some bias ...
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Following a smoothing filter of a biological signal

)Following a smoothing filter of a biological signal. y[n] = Ay[n − 1] + Bx[n − 2] Please find the transfer function in the z-domain and find the impulse response function of this filter.
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Digital lowpass filter causing aliasing

I'm writing a biquad filter program in C++, using the LBJ Cookbook as the source for the formulas. https://webaudio.github.io/Audio-EQ-Cookbook/audio-eq-cookbook.html The lowpass filter that I've made ...
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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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Designing digital low pass filter with low pass-band group delay

I'm interested in specifying a digital low pass filter with low (and near constant) pass band group delay. I tried python's spicy.signal.minimum_phase to transform ...
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Amplitude response of Lynn's low pass filter at the 3dB cutoff frequency

I am referring to the calculations in https://courses.cs.washington.edu/courses/cse474/18wi/labs/l8/QRSdetection.pdf for the second order Lynn's low pass filter. On the third page, the author mentions ...
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Butterworth-like filter with no zero at Nyquist?

I have an old digital synthesizer that has a Butterworth-like 2nd order filter with resonance. However, with high frequency tones it appears there is no steep cutoff near Nyquist (I am sure it is the ...
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How do I sort out my window sinc low pass filter

I started writing a windowed sinc low pass filter, but I cannot seam to get the code figured out right. I followed these two links http://doctord.webhop.net/Courses/textbooks/Smith_DSP/dsp_book_Ch16....
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How to come true the convolution with a 2-D array in frequency domain with python

I use the pretty simple example used in many books to understand the convolution in the frequency domain. But I cannot find the real results. ...
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Bandpass filter vs sequential high and lowpass filter in Matlab: weird difference

I am trying to bandpass a neural signal acquired at 20kHz between 0.5 and 100 Hz. I have tried to do it in two ways. The first way is to sequentially highpass and lowpass the signal and the second one ...
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Butterworth filter's gain formula does not agree with R's `signal` package

I'm trying to calculate the Butterworth filter gain. If I use the formula mentioned on Wikipedia: $$ G^2(\omega) = \frac{G_0^2} {1+\left(\frac{j\omega}{j\omega_c}\right)^{2n}} $$ I don't get a ...
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simulink discrete integrator block problem

I am testing the Simulink discrete integrator block as shown in the picture below. The simulation is fixed step with $T_s = 1e-5$ and the cosine wave block setting and the scope display is also shown ...
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Filter recognition from transfer function

I have a filter with this transfer function in the z-plane $H(z)= z^{-k}$. Which type of filter is this (BP,LP,BS)and why? I have a delay filter with zero/poles equal to zero and the magnitude ...
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216 views

Block diagram of M-PSK modulation and demodulation

I have come across this quadrature modulator block diagram in many books and websites: I've read that the quadrature modulator allows to realize many different digital modulations, including ...
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How to apply an anti-aliasing filter before downsampling

I have an eeg signal with two channels (f3m2 and f4m1) which is divided into epochs. I want to augment the data by taking every 5th sample. I can re-use the discarded samples to create 5 versions of ...
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Sinc3 Filter in FPGA

I working on FPGA block which requires an Sinc3 Filter for Sigma-Delta ADC coming in. I read about it and Sinc filter, is filter with frequency response of sinc, that means its just a moving average ...
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44 views

Why use both a high pass and a low pass filter in a Butterworth implementation for noise reduction?

I am a new to audio processing . I want to develop an application that reduces audio noise using a Butterworth filter. I found some existing code doing this, but I still do not understand the use of ...
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How can I generate an ideal 2D low-pass filter in MATLAB?

I've been tasked with creating a 32 x 32 half-band low-pass image filter in MATLAB. My thinking is to generate the ideal filter mask in the frequency domain and compute the corresponding convolution ...
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Implementation of IIR filter

Suppose we have a discrete input waveform (with sampling frequency Fs = 32*56e9). We want to filter this waveform with a filter that has two complex conjugate poles (at 22 GHz) and one zero (at 17GHz) ...
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Analogue Filters (Picking the right filter!)

I'm new to Analogue and I'm trying to find the Ideal filter for the following specifications: $0.1\ \rm dB$ ripple Cutoff Frequency $F_c = 80\ \rm{kHz}$ An attenuation of $40\ \rm dB$ at the stop-...
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32 views

FIR Filter 3dB Frequency

I am new to signal processing and I want to calculate the 3 dB - cut off frequency of this FIR filter, which has the following transfer function: For the evaluation i need to replace the z with and ...
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52 views

Is it possible to specify number of taps and cutoff frequency independently?

When specifying the properties of a moving average filter, is it possible to specify the number of taps and the cutoff frequency? My guess is no since taps (the number of samples in a moving average ...
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How to interpret frequency response of moving average system in discrete time signal processing?

Excerpt from Discrete Time Signal Processing by Alan Oppenheim: The text says this can be considered as an approximation of a Low Pass Filter. A low pass filter in continuous signal system is ...
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What are the equations for magnitude plots of the common IIR filters? (Are the ones I have so far correct?)

I need equations that describe the magnitude plots of basic IIR filter types. I had looked into this a few years ago and saved some equations but it only covers part of what I need, and I can't recall ...
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What is the decay rate (time constant) of two One-Pole LPF's cascaded in series?

If you have a One-Pole LPF, and set the cutoff frequency to $\frac{1}{2πt}$ where $t$ is the time to $\frac{1}{e}$ amplitude, it will provide an exponential decay in response to a step function (eg. ...
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Is there an equation that will graph the shape or predict the maximum amplitude of a single sample impulse fed through a One-Pole LPF?

If you feed a single sample impulse of a given amplitude through a One-Pole LPF you get an envelope that looks like this: The output of the LPF from its peak will settle into an exponential decay ...
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LPF and HPF filters in ENVI

Since we know about convolution filter in image processing, it is basically a matrix applied to an image and a mathematical operation comprised of integers and it works by determining the value of a ...
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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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53 views

Performance bounds for low-pass filters

Precisely how does the performance of an FIR filter depend on its design criteria? To illustrate, here is a specific question that probably does not have a convenient answer: The Parks-McClellan ...
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Average identical sweeps or lowpass filter sweeps first?

There are 5-10 replicate sweeps of measurements that are meant to be averaged. I also typically lowpass filter the signal at 2000Hz. The target signals are in the 0-100Hz range, and have, for lack of ...
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54 views

Downsampling after a highpass filter

Question: The following sentence is not clear to me (especially why down-shift occurs). Could someone explain it please? On the other hand, downsampling the output of the highpass filter down-shifts ...
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Difference between the average operation and the application of the equivalent LPF

I would be glad if someone could answer my question. I have a bit stream of data and I want to extract the low frequency component. When post processing the data I can calculate the average value over ...
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103 views

Converting a lowpass filter to a highpass filter. FIR filter-type 1

I was told that in the FIR filter type I, the impulse response of a highpass filter $h_H[n] $can be obtained as follows, $$h_H[n] = \delta[n − m] − h_L[n]$$ where $h_L[n]$ is the impulse response of a ...
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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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Output of LTI (in time and frequency $\omega$ domain) : when input goes through LPF

I would like to raise a mathematical question : Let's say we are been given : $$x(t) = \begin{cases} \cos(\pi t) & |t| \leq 0.5 \\ 0 & \textrm{otherwise} ...
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interpreting the post filter features in a sensor data

I am new to signal processing and I am working on Filtring signals(using basic analog filters, FIR filters, and IRR filters), for Human activity recognition, using sensor data, I Extract the features ...
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53 views

Low-pass filters not producing smooth output

I'm relatively new to this material, so apologies in advance if I'm missing something obvious. I'm trying to smooth some very noisy signals. What I observe is that if I apply an ewma, even with a ...
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How to determine the type of a digital filter given its expression?

I'm trying to understand a variant of the filter presented in http://www.stockspotter.com/files/PredictiveIndicators.pdf in the "Code Listing 1.". Its expression is given as follow: $$y_n = ...
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Weird ringing at signal start and end for default Matlab lowpass filter

**FIND UPDATES BELOW THE ORIGINAL QUESTION TEXT: I am trying to lowpass filter electrophysiological data and I see ringing near sharp transients at signal start and end. Ringing at start: Ringing at ...
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Matlab Filter designer not working, how come?

Before reading any further, to give you on some insight on the output level of the oscilloscope picture's the ~340mV green signal is normal. If you know me I posted a question as to why its 340mV but ...
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101 views

Mitigate floating-point numerical errors for very-low corner frequency low-pass filter with DSP

I'm designing a low-pass filter for a digital signal processing application that ideally just passes a very small bandwidth above DC. I'm using an IIR biquad filter for this, where the coefficients ...
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Output of IIR filter not matching the frequency response - Proximity to fs/4

After not having dealt with digital filters for a long time, I have now been playing around with filter design in octave and I am observing a behavior which I do not understand. After designing a low-...
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What is the purpose of the recurrence relation in low and high pass (audio) filters?

Newbie here. I'm familiar with time and frequency domains from math. I think I understand what low and high pass filters do, sonically. But digging into an implementation of ...

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