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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147 views

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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75 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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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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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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172 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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48 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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1answer
150 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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428 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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259 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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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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120 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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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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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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52 views

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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51 views

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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588 views

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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68 views

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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324 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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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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40 views

Next steps for analyzing this PWM algorithm and choosing a low pass filtering technique?

The Broadcom BCM2711 GPIO controller used by the Raspberry Pi has a hardware PWM implementation option using an algorithm that provides an average value defined by a rational fraction $N/M$ defined as ...
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Partially aliasing in Signals

I have read a paper about super resolution where signals are used that are partially aliased. here the paper If the sampling rate is smaller than the 2*max frequency but greater the max frequency, ...
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Filtering via Convolution and Multiplication… Why different results? *Code and image*

Image and MATLAB code are below. I am doing Complex Down Conversion (IQ Sampling) to 0 Hz and using a Low Pass Filter after it to remove an unwanted conversion product. I start with 500-1000Hz ...
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Continuously tunable low-pass filter that “interpolate” wavelet filter for multi-resolution analysis

I am using wavelets to analyse some complicated 1D signal, where I am able to come up with multiple filtered signals with different level of details. However, the cutoff of wavelet filters follow a ...
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102 views

A one-pole LPF (6 dB/oct) has a step response to $1/e$ amplitude of ${\tt time} = 1/(2 \pi f)$. What would the response time be of a 3 dB/oct filter?

I was instructed in another question here that if a one pole (6 dB/oct) low pass filter is fed a discontinuity (ie. going from 1 to 0) it will take ${\tt time} = \frac{1}{2\pi f}$ to reach $1/e$ ...
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Is it normal that a DAC outputs spikes?

I'm using a Raspberry Pi 2 and an AD/DA Board, with no extra circuit. Reading on the internet though, I found that DACs need a low pass filter in their output, and I don't understand if the behaviour ...
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83 views

Deriving expression for the DTFT of a rectangular window

Looking at the picture above, how did the author get from point A) to B)? My Approach: Multiply A) by $e^{j\omega/2}/e^{j\omega/2}$. Now I am stuck with simplying the numerator.
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LowPass Filter & Window *Img & Code* - Frequency Response has no lobe roll off

Not sure if I am doing something silly but I am not seeing lobe roll off on the frequency response of my windows and the low pass filter I made in MATLAB. Please can you help ... several hours just ...
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Correct way to build a basic filter bank (ie. for simple multiband audio processing)?

I need to build a filter bank for multiband processing. Last time I tried I was just starting at coding/DSP so I failed and didn't get a flat spectrum out of it. I just want to know the basic ...
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360 views

What is the step response curve of a second order low pass filter? And what if it is set for resonance?

I am doing a lot of audio synthesis DSP where I need to use low pass filters to shape the decay of an impulse. I understand that a one pole filter fed a discontinuity, say from a steady state of 1's ...
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223 views

Can I use a transfer function to filter noise?

I want to make it simple! I want to filter white noise with a transfer function and it's going to be zero phase. Assume that we have our low pass filter. $$G(s) = \frac {1}{1 + Ts} $$ Where $T$ is ...
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59 views

Ideal low-pass filter in the Frequency Domain

I try to create a low-pass filter to apply it for an image. $$H(U, V)=1 \text{, if }D(U,V) ≤ D_0 \text{, and } 0 \text{ otherwise}$$ and $D(U, V) = \sqrt{U^2 + V^2}$ ...
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859 views

Consider an ideal low pass filter $H(\omega)$, and the input to this filter is the periodic square wave $x(t)$. Find the output $y(t)$

The solution to the problem is $$y(t) = 5 + \frac{20}{\pi} \sin(\pi t) + \frac{20}{3\pi} \sin(3 \pi t) $$ and to get that the solution says to find the Fourier series expansion of $x(t)$ and I am ...
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136 views

Implementation of Filters in Python

I've implemented 2 filters in Python I would like to know if they look OK or not.. I've implemented an lowpass FIR Hann Filter and an lowpass IIR Chebyshev type 1 filter. My plots look like the ...
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242 views

Lowpass Hann filter in Python

I'm trying to design a FIR lowpass filter using Hann windowing in Python but I don't know where to start from... I have fc1,fc2, ft, rp and rs as parameters. This is my Python code: ...
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Fundamental component estimation

I am dealing with phasor estimation (fundamental component extraction primarily), and i am using sliding window DFT (which happens to be very popular for phasor estimation). Now at nominal frequency (...
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172 views

A filter with low phase shift or no phase shift at all? Which one? [duplicate]

I'm seeking a good advice for a filter. Can you help me? Right now I made my own simple filter. Not sure what I'm doing, but it seems to work. ...
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Can't implement correctly Python IIR and FIR Filters

I'm trying to implement 2 lowpass filters and see the difference between them from plots( one FIR filter that needs to be designed with the Hann window method and another IIR filter using Chebyshev ...
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Remove aliasing caused by scanning a wave file at arbitrary playback rates

I am writing a sound generator that needs to scan through audio samples at an arbitrary rate. When the sample is played at it's original rate, it sounds fine. But when I change the playback speed, it ...
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69 views

How is downsampling and low-pass filtering done in MS-SSIM?

I am just studying the Multiscale Strutural Similarity measure for image quality and going through the original paper [1]. I think I understood the basic ides and "regular" structural similarity, but ...
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268 views

Amplitude reduction of Simple Moving Average on sinusoid

When a -causal/non-centered- simple moving average filter (arithmetic mean) with length $n$, is applied to a sinusoidal curve with period $p$, and the resulting curve is compared to the original input ...
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How to difference a loud sound (playing notes), from a soft noise in spectrum. (Pitch detection with bass)

I'm trying a program that outputs the bass line that you are playing. I have some arrays from a big one with the sound in time domain, that are splited (Hann window). Later, I do the FFT, then I get ...
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What is absolute ripple specification and how does it arrive in low pass prototype for Butterworth?

Digital Signal Processing by John G. Proakis, Dimitris G. Manolakis(4th Edition) gives the prototype function for Butterworth low pass filter in an analog system which is fine till the point where the ...
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512 views

How do Anti-Aliasing Filters filter the signal?

I have programmed a anti-aliasing filter that uses the fourier-transformation and makes a perfect cutoff on my desired cutoff frequency for downsampling without aliasing. I have read about other ...
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How to use low pass filter in Matlab for discrete data? [closed]

As see in the picture, there are high frequency noise in the signal. How to design a low-pass filter to eliminate the noise? How to apply this filter in Matlab?
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How to separate a low amplitude signal of same frequency but different phase

I have a signal consisting of two sine waves of same frequency but have different phase (and also a lot of HF noise). Their amplitudes differ by about $120\textrm{ dB}$. How to I go about separating ...
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54 views

Lowpass Butterworth filter equation

I am using a 5th order lowpass Butterworth filter with a varying cutoff frequency, $f_c$, to smoothen some data coming from a spectrometer. An example of a spectrum, plotted with the filtered data, ...

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