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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Side Lobes in the Magnitude Response of a Low Pass FIR Filter

I have the impulse response (from the filter coefficients) of an FIR filter obtained from MATLAB's "interp" function using the command: [y, b] = interp(x, 5); % where b contains the interpolation ...
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Do you recognize this discrete realization of a low pass filter?

I have a simple 1st order lag filter implementation that performs well, shown in the block diagram below. This is legacy 'code' we've been using for many years, the original developers have long ...
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How does window length influence cut-off frequency of filter and group delay?

I'm attempting to interpret the following function. To my understanding, this aims to implement an FIR low-pass filter with a Nuttall window. Then, it filters the signal by a simple application of the ...
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790 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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Design of Parks-McClellan Lowpass Filter

Can we design Parks-McClellan Lowpass Filter with only sampling frequency of 12KHz and cutoff frequency of 4KHz and order of 30? I went through Matlab help, where we need parameter like passband ...
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403 views

python rewrite lfilter (iir) with for

It's a beginner question, but useful to users from python - signal.lfilter, I was using lfilter from Find reverse one pole ...
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40 views

Correct signal analysis flow (Wind Turbine vibration)?

I have vibration data from WT (gearbox) sampled at 25.6 kHz. From a previous post I received a lot of good recommendation. What I am trying to do: Find early stage bearing faults by using an ...
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63 views

How does this represent a low-pass filter?

I am faced with the following code snippet to get an understanding of a F0 estimation algorithm (DIO). Have a quick look below: ...
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46 views

Coefficient weights of Simple Moving Average (SMA) on SMA

A simple moving average (SMA: arithmetic mean) is a low-pass FIR-filter. When you cascade 2 SMA's with a window of length $n$, so when you apply the second SMA on the output of the first SMA, and you ...
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Low pass filter implementation with programmable cut-off frequency for inclinometer

My application is an inclinometer. I would like to design a low pass filter with programmable cut-off frequency ranging from 0.1Hz to 20Hz using CMSIS DSP library provided by ARM. The filter may be ...
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52 views

Low pass equivalent of bandpass white noise

Let $$n(t) = Re\{z(t)e^{j2\pi f_ct}\},\ $$ where $z(t)$ is the low pass equivalent of white noise $n(t)$. We know the autocorrelation of $n(t)$ is $$R_n(\tau) = \frac{N_0}{2} \delta(\tau),\ $$ $\delta(...
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35 views

A communication system

I am solving the following problem as an exercise. I have a signal $$z(t) = x(t)\cos(wt) + y(t)\cos(ut)$$ and we assume $x,y$ to be band-limited continuous time signals. In the frequency domain we ...
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Cutoff Frequency of Low Pass Filter for Image Processing

Im working on an image processing problem where i need to implement lfilter from a paper. The filter is done in Frequency domain. In the paper stated that the filter is a low pass with following ...
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44 views

Result length and width of a lowpass FIR filter

I am designing a 50-tap lowpass FIR filter in Verilog. I have a really simple use-case: I have a vector that is the sum of two sine waves, and I want to filter the higher frequency one out. My data ...
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57 views

Frequency conversion in IIR lowpass-to-lowpass transformation

We use $\ z^{-1} \xrightarrow{} \frac{z^{-1}-\alpha}{1-{\alpha}z^{-1}}$ and $ \alpha = \frac{\sin(\omega_c^{'}-\omega_c)/2}{\sin(\omega_c^{'}+\omega_c)/2}$ for a lowpass-to-lowpass frequency ...
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39 views

signed 2's complement of a negative number for Integer = 3 and Fraction = 9

I am working on signed 2's complement for my fractions coefficients. Below code can be used for positive inputs. However for a negative 2's complement when I added LSB with 1, then an error pops. I ...
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52 views

Moving Average Filter's Magnitude Response

I am working on filtering of data using the Moving average filter in MATLAB. My data is recorded temperature values on the Y-axis and Time(in seconds) on the X-axis (I'm getting the magnitude response ...
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103 views

What impact have different types of border-handling on high pass or low pass filtering?

When high or low pass filters are being applied to an (grayscale) image, the borders need to be handled separately. They could be filled with 0's or 255's (b/w), repeat the nearest pixel value, or ...
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40 views

How to derive 2nd order Butterworth condition for the damping coefficient mathematically?

The magnitude of 2nd order low pass filter is given as $$|H(\omega)|^2= \frac{1}{(1-(\frac{\omega}{\omega_o})^2)^2+(\frac{2\zeta\omega}{\omega_o})^2}$$ Now in order to achieve maximally flat within ...
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Are high pass/low pass filters FIR filters?

I am trying to understand the basic categories of DSP filters, and it seems that the two main groups are FIR and IIR, however I'm not sure how to categorize high pass, low pass, band pass, and band ...
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36 views

3 dB bandwidth of a filter

I am solving one of the question from signal processing about calculating the 3dB bandwidth of the filter. But I am stuck once I got the magnitude response of the filter. Can someone help me with this?...
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70 views

Calculate input impedance from S-parameters

I wrote this simple matlab code to calculate input impedance of a low pass filter but not sure whether all the steps are correct. * First attempt ...
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Bandpass filter is not working as expected

The sampling rate that I have currently is at 384kHz and I want to downsample it down to 44.1kHz. I want to use a bandpass from 5kHz to 200kHz but I am only able to bandpass up to 192kHz for some ...
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Remove noise from distance calculated from accelerometer data

I got distance calculated from accelerometer raw datas using double integral accelerometer.I attached the image below.But it shows noise with it.Please help me to remove this noise.
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660 views

Low-pass filter with varying cut-off frequency over time

Is there a novel way to create a low-pass filter (Finite Impulse Response Filter) with varying cut off frequency over time? For example, I have a white noise that is 10 seconds long sampled at 44.1 ...
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53 views

aliasing in image processing

I know that aliasing occurs when a signal is subsampled. If the sampling rate is lower than twice the max frequency in a signal, aliasing occurs. How is it in pictures? as far as I know, a sinc-filter ...
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56 views

Why notches in sinc filter response

Below response shows sinc1,sinc2 and sinc3 filter response. I understand that notches in the frequency response happens at the output data rate of the sigma-delta ADC. But I am not able to figure out ...
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39 views

FIR filter with relaxed transition band

Is there a way to design a lowpass FIR filter with a more relaxed transition band than what MATLAB FilterDesigner tool generates? What I intend to do is to reduce number of taps needed to implement ...
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113 views

Low pass filter output showing instability

I am fairly new to DSP, and I'm trying to implement the Pan Tompkins algorithm for QRS detection of ECG signals in MATLAB. The first stage of the algorithm consists of a second-order low-pass filter. ...
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56 views

Decimation Question about using a low pass filter before downsampling

I have a bunch of audio files that have a sample rate of 380kHz, however I would like to reduce this sampling rate to 44.1kHz. From doing some research online, it seems like I will have to use a low ...
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Transfer function of second order notch filter

Can anyone mention the transfer function of second order notch filter to remove the line frequency of 50 Hz, in terms of frequency and sampling rate. Just like for Low pass Butterworth filter as, $$ ...
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250 views

Analog Filter Prototype to Direct Form Second Order Cascade

I've been using the Faust programming language a lot lately for experimenting with DSP, and I've been digging into their implementation of an Elliptic (Cauer) Lowpass filter. Here's an example of such ...
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782 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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81 views

Calculating the 3dB frequency of an nth order low pass filter and nth order high pass filter

I am using the 6th order high pass filter in the C code. And the cut-off frequency selected for it is 150 Hz and the sampling frequency being used is 32000Hz. Now, I want to calculate the 3 dB ...
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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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427 views

windowed sinc filter in matlab

Hello i'm designing a low pass filter windowed sinc in matlab ...
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38 views

Ideal low pass filter output at given sampling frequency

Consider the signal $\cos(30t)$ sampled at $w_s=40 rad/s$ using a unit impulse train. The sampled signal is filtered with an ideal low pass filter with unity gain and cutoff frequency $w_c = 40rad/s$. ...
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How to draw the magnitude plot of a variable slope low/high pass shelving filter? (eg. as a function of cascaded shelving filters)

I am interested in making a magnitude graph of a variable slope low/high pass filter. I would like to set slope in dB/oct and a cutoff pitch. The y-axis should be amplitude from 0 to 1, and the x-axis ...
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Why when you use any filter, it results first a steepness at the beginning to a certain level?

Is there any tool to avoid that? For instance, I wish after filterin my signal, the filtered signal start from a certain level, in other words, at the offset level. In this case, I've use Butterworth,...
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Remove AC component from the mixed signal using an elliptic filter

I have a signal like this: $s(t) = C + a \cdot sin(2 \cdot \pi \cdot f \cdot t)$ where $C$ - arbitrary constant, $f$ - frequency of AC component (Hz) and $a$ - amplitude of AC component. Parameters:...
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How to remove the bump from the signal using filters?

I want to have only the slope of the signal. How can I do? I have tried to apply some filters but so far I have not been able to hit the nail on the head. I use Matlab.
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Designing ideal lowpass filter in the form of FIR

How to design a ideal lowpass filter by cutoff frequency of π/4 in the form of FIR filter by 64 samples using matlab?
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Using a low pass filter to interpolate signal

In my DSP university textbook, the interpolation process is described as follows: In order to represent a baseband signal $x[k]$ at an increased sampling rate with the same shapes of its time-...
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Droop compensation - How to do it?

Lets say i have a LPF response that has some kind of droop (some attenaution in the passband, usually could be due to cic filter how to make CIC compensation filter,,,, or can also be due to large ...
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137 views

Digital low pass filter vs continuous low pass filter,?

What is difference between both implementations of low pass filter? Discrete/digital implementation and continuous implementation? As far i am able to understand In case of discrete implementation,...
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53 views

Prove the following DFT for a periodic sinc sequence or ideal lowpass filter

I need to prove the following DFT for a periodic 𝑠𝑖𝑛𝑐 sequence or ideal lowpass filter: $\sqrt{\frac{p}{m}}\frac{sinc(\frac{\pi np}{m})}{sinc(\frac{\pi p}{m})} \stackrel{DFT}{\longleftrightarrow} ...
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570 views

Filtering on time or frequency domain?

I'm applying an ideal filter on the frequency domain. My code below: ...
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163 views

IIR Direct FormII Filter second order in VHDL, false output

I am trying to implement an IIR second order in Direct FormII in VHDL. To make it easier to understand for me and to avoid former timing issues, I implemented the operations sequentially. In my ...
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98 views

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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Why is the frequency measured in radians in filter design?

This is my first time posting a question, so sorry if my articulation is not proper. I'v just started out with FIR filter design and I see the domain being -$\pi$ to $\pi$. Now I understand that ...

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