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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32 views

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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51 views

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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23 views

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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144 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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31 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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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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43 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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35 views

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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39 views

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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208 views

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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48 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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23 views

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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83 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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127 views

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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48 views

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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69 views

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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70 views

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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94 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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38 views

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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40 views

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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65 views

What is the multiplication rate in FIR filter

Consider a system implementing a rational sampling rate change by 5/7: for this, we cascade upsampler by 5, a lowpass filter with cutoff frequency pi/7 and a downsampler by 7. The lowpass filter is a ...
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112 views

Pre-Warping is not working on bilinear transform

New here and I just wanna ask the question of what happens when your pre warping doesnt work on your bilinear transform? I am assuming my isnt working as part of my research I have read that the ...
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38 views

How to simulate a signal of a particular frequency according to the number of points in a period of the signal?

I have one period data ($n$ points in total) of a signal. I want to generate a periodic signal with a total of $m$ points and corresponding signal frequency of $F$ according to this data. How do I do ...
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113 views

number of multiplications per second required by the system

Consider a system implementing a rational sampling rate change by 5/7: for this, we cascade upsampler by 5, a lowpass filter with cutoff frequency π/7 and a downsampler by 7. The lowpass filter is a ...
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81 views

minimum oversampling factor for D/A converter

Consider a D/A converter for audio signals consisiting of a zero-order-hold interpolator followed by a continuous-time lowpass filter with positive passband between 0 and 20KHz and stopband starting ...
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55 views

What is the difference between FIR1 and FILTFILt in MATLAB?

In MATLAB there are filters with 0 phase filtfilt and ordinary FIR1. When I filtered a group of simulated data, I found that filtFilt was superior to FIR1 in terms of phase delay. I know the ...
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Determining the right order of time-domain low pass filter for desired cutoff frequency

I've been stuck on a problem regarding complex demodulation of a signal for a while and wondered if anyone could help. Suppose I have a signal $X(t)$ such that \begin{align} X(t) &= A(t)\cos(\...
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124 views

Number of multiplication operations needed in rational sampling rate change with IIR Butterworth filters

I am trying to get a general sense of how many multiplication operations are needed for a 4th-order Butterworth filter (IIR filter) with a rational sampling rate change. I am excluding any ...
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669 views

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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111 views

Design of a low pass filter with Red Pitaya's FPGA

I'm trying to design a low pass filter in Verilog for use on a Red Pitaya's FPGA (Xilinx® Zynq®-7010). All I'm trying to get the low pass filter to do is to obtain the DC component in the signal. The ...
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64 views

Complex signal low pass filter

I'm trying to implement a low pass filter in python for a complex signal but the output doesn't look right. I've created a simple example below where I've mixed a 15Hz complex sine wave and a 30Hz ...
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Problem with implementing DC offset for streaming data

I am new to the DSP world. I'm trying to run a raw input signal through a LPF, remove any DC offset, amplify the signal, and then decode the signal. The problem with my code seems to be the ...
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22 views

Low pass filter output

What will be the output when a square wave of time period 1sec is applied to the input of LPF of cutoff frequency 1Hz. Please help me, I am not getting the exact expression. What if cutoff of LPF is ...
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Filtering a square signal with a median filtering to preserve the edges

If needed, you can find my first post for this problem here. I am trying to clean the following signal: As proposed in the comment, I tried to use this post proposing 2 methods: median filtering and ...

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