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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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Determine filter type using recurrence relation

Given the recurrence relation: $y[n] = x[n] + 0.5y[n-1]$ I want to determine the filter type (i.e. LPF, HPF etc.) I try to use Z transform, and get that the the transfer function is $H(z) = \frac{2z}{...
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What type of low-pass filter to use for gyroscope filtering in control application?

I am using a gyroscope to generate a feedback signal that drives a motor to resist rotation, just as in a camera gimbal. The gyroscope is sampling at 32 KHz with a bandwidth of 8 KHz, and my control ...
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34 views

How to keep low frequencies in DCT

How can I keep a percentage r of the low frequencies of a Nx1 signal x using the Discrete Cosine Transform of it? Is it simply zeroing all but the first rN elements of DCT(x)?
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Low pass filter preserving amplitude

Are there any types of low pass filters that preserve the amplitude and phase? The one that I am aware of, sometimes called an exponentially weighted moving average does neither. First order Low pass ...
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how can I design Chebyshev filter with 5th-order polynomial and 0.001%-allowed ripples?

I'm very beginner in signal processing. I need to design a Chebyshev filter with 5th-order polynomial and 0.001%-allowed ripples by using matlab as I found in a paper. I'm filtering pressure data ...
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45 views

How to filter an OFDM signal? [closed]

Across the channel bandwidth there shoudd be 100 RBs (central 1200 sub carriers in a 2048 bin). Max power normalized to 0dB, the first OOB lobe should be -34dB. This 1st lobe on either side is at 5 ...
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Constructing a lowpass digital differentiator such that maximum error is $n$ dB for passband

I want to construct a lowpass digital differentiator with uniform-interval samples such that error from ideal differentiator is $n$ dB in magnitude at maximum for the passband up to frequency $\...
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104 views

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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Lowpass-filter necessary before DFT?

I'm trying to distinguish eletrical engines by the magnetic field they create. I have no idea whether this is a smart idea, it's possible at all, whatsoever. However it brought me to a basic question ...
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1answer
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Why do cutoff frequencies of a high-pass digital filter differ from the ones i used to transform it from a low-pass analog filter in MATLAB?

I need to transform an elliptic analog low-pass filter to a digital high-pass filter but i'm having a problem because the resulting filter has lower cutoff frequencies than the ones i set. Here is the ...
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1answer
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Using Parks-Mcclellan (or others) for FIR differentiator?

I have never seen the use of Parks-Mcclellan for differentiator - most uses tend to be lowpass filters. Is this because Parks-Mcclellan implementation of FIR differentiator has numerical problems and ...
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LP to BP transformation steps

Considering the following problem, What i know to convert from LP signal to BP signal is to: Draw the FD of the LP equation From it I can draw the FD for BP From this graph I can deduce the equation ...
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115 views

Why does my low pass filter diverge below 7000 Hz?

I'm trying to create a LPF, using language JAVA. My first aim is to understand how filters design is working and the second one is to create a "home made" equalizer with "home made" filters. To help ...
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188 views

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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1answer
19 views

How does cascading low pass modules affect pass band ripples?

This question 10.21 is taken from GATE IN paper 2015. I don't understand the answer given, I mean why is the frequency response at the pass band frequency considered to be $(1-\delta)$, isn't the ...
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1answer
32 views

Low pass to low pass transformation coefficient?

I am unable to solve this question, 10.10 from GATE IN 2004 (a previous year question paper for an exam targeted at engineering graduates in India.) So I tried to solve the 10.10 by considering the ...
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Using a Passive 1st Order RC filter to Extract DC Component

I am trying to extract the DC component out of a PWM signal produced by the MCU using a LPF. I understand that 1st order RC filter is looked upon as being amateurish because the gain in the passband ...
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2answers
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Cascading a filter with itself to form a higher-order filter?

I've been given an audio signal with some high frequency noise. The professor gave me the system function of a lowpass filter that gives me control over the cutoff frequency: $$H(z)=\frac{1-\alpha}{2}...
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4-phase FIR LPF in MATLAB

I'm trying to create a low pass FIR filter using the coefficients I found in ITU 1770-3 on page 18. This is the last piece of the puzzle for an audio loudness metering algorithm I'm working on. I'm ...
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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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1answer
44 views

Time-domain LPF not showing expected behavior

I am trying to implement a simple first-order Butterworth Low-Pass filter in Python. I have some code that makes use of scipy.signal.butter and scipy.signal.filtfilt. It works fine, but I wanted to ...
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Parallel Cascaded FIR Filters

I have a relatively simple question. I know if you connect multiple LTI systems in parallel, overall system's frequency response is the sum of each LTI system's frequency response. Therefore, what ...
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1answer
119 views

Detecting fundamental zero crossing point

I am looking for ideas from the more experienced members on algorithms for determining the fundamental zero crossing point of a 50 or 60 Hz signal. The fundamental zero crossing point is then used as ...
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3answers
153 views

How to Classify Image Filter as Low Pass Filter (LPF) or High Pass Filter (HPF)?

I am currently reading on the topics of image filtering and convolution kernels. While the process of convolution is clear to me, I do not understand, how one arrives at the statement, that a certain ...
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1answer
109 views

signal reconstruction [closed]

I'm new to DSP so the question might seem a little bit stupid: When using a low pass filter (say Butterworth filter) with Python, I came across an algorithm with which I can reconstruct my signal ...
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129 views

digital IIR filter delay and oversampling

Can oversampling decrease the delay of digital IIR filter? Imagine there is some digital signal going into processor that applies low pass filter.Lets say its 1 KHz sample rate and the filter is ...
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1answer
56 views

Problem with 1st order Massberg LPF [duplicate]

I'm trying to implement this filter in title by following the book "Designing Audio Effect Plug-Ins in C++" By Will Pirkle Problem I'm facing is the magnitude response error when comparing against ...
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2answers
70 views

Initialize Hi Pass Filter

I want to remove the DC from a ADC, so I designed a two-pole, 1 Hz high-pass Butterworth filter for a signal sampled at 10kHz. The filter coefficients are: ...
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Issue with the Massberg Analog-Matched Low Pass Filter

Implemented the filter mentioned in title using Octave and couple sources Vicanek and Zeitlin (LPF.cpp). Got filter working otherwise but, ... when tested the responses against 'analog model' of the ...
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1answer
54 views

Simple question about Sinc()

Suppose I use the ideal lowpass filter eq to attempt creating a IIR filter using it : $$ h[n] = \frac{\sin(\omega_c \, n)}{\pi \, n}, \qquad -\infty < n < \infty $$ Obviously, I can't really (...
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1answer
80 views

How can I determine the order of filter?

This is my first study about signal analysing. I'm very confused about filter order. My problem is how can I know whether its 12-th order, or 2nd order like the book says so? I already knew that slope ...
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1answer
285 views

How to filter out those outliers

I'm struggling to filter some data from an accelerometer. I need to do it in python (and not just on the device collecting the data) to fix the data I have, so that I can build some classification ...
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How do you initialize the output of a second-order-section filter?

I've got a 4 stage second-order-section filter. When I turn this filter on, it assumes it is starting from zero and takes forever to converge on the actual signal. For example, let's say I have a ...
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CCDE processing vs. Scilab function

I have used Scilab functions to produce a low-pass filter for an audio signal and the coefficients for the associated constant coefficient difference equation (CCDE). I then produced filtered signals ...
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3answers
61 views

Usefulness of Practical filter ouptput

If a practical filter can't remove all unwanted frequency components like ideal filter, does that mean unwanted frequency component are still present after filtering? how can we use such distorted ...
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Objectively determine the best filter to preserve peak value and width of the signal

what should be the process to determine the correct filter to smooth a force signal (impact) where the peak value (or peak values) of that force and the impulse (physics) will be used for further ...
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1answer
309 views

Frequency analysis to determine low-pass cut off frequency

I collected some data for a practical application, where the signal represents force data obtained from an impact of a punch against a force plate attached to a quasi-rigid rig (it moves once the ...
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1answer
75 views

Poles and zeros map

Given the following map of poles and zeros for some $H^L(s)$: How can I understand from the map that the given Transfer function is LPF? Hence the poles are located at the hight frequencies it should ...
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1answer
116 views

Do you recognize this filter?

I'm trying to decipher the uncommented source code of SoundBox which is a little music tracker written in javascript. There is an included synthesizer, which applies a filter on the output samples. I'...
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2answers
70 views

High/Low Pass Filters from Zero

I everyone, I'm a computer scientist but not from the signal processing community. I want to implement a real time digital low pass filter (to begin with) for a sound processing application. I've ...
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236 views

How to design a low pass sinc filter given a time constant?

How can you derive the cut-off frequency $f_c$ for a given time constant $\tau$, in order to be able to design the low pass sinc filter: $\mathrm{filter} = 2f_c \mathrm{sinc}(2f_cx)$ The formula for ...
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LC Low Pass Filter Design

I am attempting to design a low-pass filter for a subwoofer, as the audio amplifier that is connected to it does not filter any of the sound coming in, and it is getting pumped full of high frequency ...
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How to combine filters' effects?

My question is about the use of many filters on a sound signal. I found the following transfer functions for the high cut, the low cut and the pass band filter : H = K / (1 - x^2 + j.x/Q) H = K / (1 -...
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2answers
145 views

Gaussian pyramid: why needs the image to be downsampled

In the context of a gaussian pyramid, why is the image downsampled separately although the numbers of pixels are decreased through smoothing already? In my understanding, the number of pixels will ...
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1answer
147 views

How to decompose raw acceleration signals into gravity and dynamic acceleration?

I have a data from $3$-axis $50$ Hz accelerometer, acceleration over each of $3$-axis: $acc_X,\ acc_y,\ acc_z$. I want to decompose acceleration into gravity and movement components. First ...
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1answer
246 views

How to design a lowpass filter using Hamming window and sinc function

I have these three equations and have a noisy voice signal. I have to design a low pass filter of length N=1000 using hamming window technique. I have selected its cutoff frequecny 0.25 (normalized). \...
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Low/High cut filter : how does it work?

I have a question about the low-cut and high-cut filter on an equalizer. Let's say, for example, that I'm using a 15 band equalizer with the following central frequencies: 25, 40, 63, 100, 160, 250, ...
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Two zeroes at $z^2+2z+1=0 \iff z=-1$ corresponds to a double damping at the Nyquist frequency?

If a transfer functoin has two zeroes at $z^2+2z+1=0 \iff z=-1$, then this corresponds to a double damping at the Nyquist frequency? Is this standard knowledge?
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How to Classify a Kernel as Low Pass Filter (LPF) or High Pass Filter (HPF)? How to Transform an LPF Kernel into HPF Kernel?

The filter impulse response is [1/9 1/9 1/9;1/9 1/9 1/9;1/9 1/9 1/9]. how do i determine whether it is an Low pass filter or a high pass filter. If this is a low pass filter how do i convert it to a ...
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Estimating frequency when there's little isolation between signal and noise frequencies

Say I have a signal which is guaranteed to have a frequency between 110-120 Hz but is corrupted by interference signals that're very close to this frequency range. For example, let the interference ...