# 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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### Low pass vs band pass filter

I've been reading some EEG papers where the authors use a bandpass filter at, say, 1Hz and 30Hz. I've also seen some accelerometer papers where they bandpass at 0.5Hz and 10Hz What is the difference ...
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### Savitzky-Golay filter parameters

I am trying to smooth a series of data in order to obtain a continuous function that could represent that given data set. It came out that the Savitzky-Golay method could be a good way. Now, I don't ...
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### Implementation of basic 2-pole low-pass filter

I know this question has been asked to hell and back from many people, and that it will probably get downvoted until it's deleted, but please bear with me. I am designing a sound engine for one of my ...
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### Understanding audio downsampling code (JavaScript) and adapting to a different ratio

I inherited responsibility for some audio downsampling code that I don't fully understand: ...
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### Malaysia Flight 370 Image Processing

I wish that all those people on that flight were with us, and maybe they still are, as I like to think they are on an island somewhere waiting to us to find them ... however, it does not look good... ...
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### Ideal Low-Pass Filter Output?

I'm very new to digital signal processing, I've been reading a text book to try to figure out this assignment at work (avionics related). I'm supposed to implement a two-pole low-pass filter with a ...
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### Designing A Filter Using SPTool In Matlab

I am currently working on learning DSP and for my course we use Matlab. I have been tasked with designing a low-pass filter using SPTool with the following specification: A Low-Pass Kaiser Window ...
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### Use recursive least square as an “actual” filter?

I am currently studying recursive least square (RLS) and as far as I understand, the setup is (for example) that we are given a process with uncertain parameters/noise and we want to adapt parameters ...
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### Lowpass : What is wrong with average filtering?

The question is : What is wrong with averaging as low pass filter ? The details : I want to lowpass filter a signal to downsample it. The constraints are : I have no RAM available and I work in ...
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### Low pass filter algorithm origin

I have been doing some research, because I used this algorithm that's very spread in the web: y += a * (x - y) or ...
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### Frequency response of a rolling linear regression

I am looking for a way to characterise the frequency response of the slope from a linear regression. We are exploring the effect of window length of the regression to the magnitude of the slope of the ...
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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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### Analytical Calculation of the Impulse Response of an Arbitrary Filter

This is a rather general question. Suppose I have an arbitrary filter, $F$, defined in the Laplace domain; $$F=k\frac{\prod_i (s+z_i)}{\prod_j(s+p_j)}.$$ How do I calculate the impulse response of ...
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### Envelope of a signal via Convex hull / Edge detection

Is there a method in order to compute some sort of edge detection / convex hull of a signal x[n] (in orange here). Here of course the orange signal is not convex ...
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### Digital Anti Aliasing Filter For Waveform Band Limiting

I am working on some waveform generation software and I am trying to figure out what the best type of filter would be to use a an Anti Aliasing filter for my algorithm. I am generating my waves in a "...
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### Why do we need to have unity gain at DC for a lowpass filter?

I have seen many times, including in a post on this forum, that it is recommended to have unity gain at DC for a lowpass filter. I would like to now the mathematical explanation.
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### How to design very narrow band, very sharp low pass filters - Only DC needed?

I am using a DSP processor to sample signals at 108kHz and I only want to get the DC part out of it. Such a high sampling rate is used because I want to use oversampling to reduce quantization noises. ...
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### Cutoff frequency of a first order recursive filter

I've implemented a very simple first order recursive low pass filter in c using the algorithm: ...
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### Difference Between Equiripple & Least Squares Design for FIR Digital Filters

For an efficient and optimized digital FIR filter design, there are two methods available broadly, Equiripple filter design & Least Squares filter design. A general method for designing a filter ...
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### LPF and HPF Confusion - Rectangular and Circular Cut-Offs

Interpreting some homework, I'm a little confused on what it's asking for. I'm asked to filter in the frequency domain (easy enough, just a fft2 and ifft2 when I'm done) a 256x256 8bit grayscale tiff ...
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### Do lowpass filters affect the integral over the signal?

For which filters, does the resulting signal have the same integral (/average) as the original? Obviously this is true for a moving average, but is it also mathematically true for e.g. a Butterworth ...
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### Is there an algorithm for second order filtering of data where the filter frequency is not known a priori?

It is well known that a moving average algorithm done in the time domain is equivalent to a filter with frequency response $\mathrm{sinc}(\omega\tau)$ where $\tau$ is the averaging time. (see this ...
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### Low pass filter with DFT

This is my first question at this site, please excuse me if I'm not asking the question properly. I have an acoustic signal of a test and I want to remove the "thin" peaks, because they don't really ...
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### Equivalent 2D mask of moving-average

I have the moving-average mask as mask = [1 1 1; 1 1 1; 1 1 1]; and then I compute the convolution 3 times ...
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### Why Butterworth filter always starts my signal from from zero mark (amplitude)?

I am trying to filter my force signal using Butterworth low pass filter. so this is the signal, I have to filter (noise frequency is around 33 Hz). So when I use Butterworth filter with following ...
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### How to test the FIR filter in C++?

I am almost done with design and implementation of my first FIR filter using C++. Its a Sinc-Windowed FIR filter designed for a cut off frequency of 100 Hz with sampling rate of 500, with a filter ...
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### Interpolated FIR filter

I am confused about this Q&A : Interpolation by factor of 2 If my input signal $$x[n]= x0,x1,x2,x3$$ then according to the threads explaination my $v[n]$ will be  v[n]=x0,0,x1,0,x2,0,x3,0 ...
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### 2D Fourier transform of Sobel kernel

Can someone explain me the highlighted text parts regarding this image ? Here is a pseudo-code of how it was created: ...
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### Does lowpass filtering and decimating improve SNR?

I did not manage to find clear answers to this question: does decimation after an appropriate lowpass filter improve the signal to noise ratio? To investigate this question, I considered data ...
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### Common Filter Types for Audio Applications

I'm beginning to write a basic "virtual analog" synthesizer and want to implement a lowpass with variable cutoff frequency and resonance. Does anyone have insight into filter types commonly used to ...
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### A Simple Lowpass Filter Behaving so Strangely

I don't know much about filter design. After reading a few articles on wikipedia I am playing with filter design and I see something weird and would like some help in understanding what exactly is ...
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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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### What did I do wrong with this simple filter build?

I tried to put everything I have learned from people here together to code my first filter from scratch. Unfortunately, it didn't go well and I'm not getting the expected output. The math/code became ...
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### Apply butterworth filter (lowpass) to a signal

I'm working on a DSP lab and I can't figure out how to apply the filter I've created to a sound. The only thing I found online that did something to my sound was ...
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### How do I smooth this noisy signal?

I have a numerical solution to a problem in mechanics. I am computing the force applied to an object as a function of its deformation and in the problem, there is an instability, due to which the ...
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### Reverse Engineering Bessel LPF (sample frequency needed)

I have the following sourcecode. For all I know, it should be a Bessel LPF at 10Hz. Is there a way to get the sampling frequence out of this? ...
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### 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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### When input data into a low pass filter, are the first several data unusable?

For example, I want to feed a DC into a low pass filter. The the filter's first several output will not have the same DC value I want. Does it mean that I need to dispose first several results? How ...
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### About designing digital filters [duplicate]

I'm currently using MATLAB's fdatool for filter design. Using that tool, I can easily design different kind of filters. For example, let's take a band-pass FIR filter with 10-40 Hz passband, and 5-10 ...
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### Understading sampling theorem and aliasing

A real-valued analog signal with a flat spectrum between f = 0 Hz, and fmax is sampled at a sampling frequency fs = 24 kHz. The sampled signal is then processed with an ideal lowpass filter with ...
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### Lowpass Lanczos filter

I am new to Lanczos filters and trying to figure out how they can be used to generate a zero-phase lowpass filter with good time-domain properties. This example shows how to implement such a filter in ...
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### Can the overlap-add method be used with varying cut-off frequency filter?

I'm writing a software analogue synth. I have been using the Overlap-add method to cheaply implement a low-pass filter using FFT. My low-pass filter has had a constant impulse response; a constant ...
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### Fractional Delay Filters and Cutoff Frequences

I am trying to implement an interpolator for arbitrary sampling rate conversion of a one-dimensional signal (a fractional delay filter). I am aware of the fact that interpolation is in general a ...
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### 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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### Spectrum analyser and resolution bandwidth

For the preliminary part of a lab I had to do, I was asked the following question: I get how to do 1.1, but with 1.2, I really don't get what's going on; I really would've thought that the resolution ...
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### 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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### Why do Savitzky-Golay filters of degrees 4 and 6 have roughly opposite ripples?

Savitzky-Golay smoothing filters of polynomial degrees 4 and 6 have frequency response with ripples of roughly opposite signs. Thus averaging the coefficients of two filters of degrees d and d+2 is an ...