# Questions tagged [filters]

In signal processing, a filter is a device or process that transforms a signal by selectively choosing specific frequencies and leaving others with appropriate gain or as it is.

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307 views

### Parameters of Butterworth filter that approximates the amplitude response of a Gaussian filter?

For a given narrowband Gaussian filter with a specific central frequency and filter width, I need corners of a bandpass Butterworth filter whose amplitude response is close enough to the Gaussian ...
459 views

### How to reduce latency under mean filter for high noise?

We have a position sensor that under some conditions receives some high frequency noise. We can eliminate that very well with a simple mean filtering. Unfortunately this causes too much lag when ...
24 views

### simple iir filter implementation in C++

I am programming the simplest way of implementing and IIR filter. However, I am struggling with the use of buffers. Do any of you have any simple implementation of an IIR filter implementing manually ...
28 views

### What does nonnegative zero-phase response mean?

I am not exactly sure what nonnegative zero-phase response means. If a filter is zero-phase (i.e. symmetric and non-causal), then what does nonnegative imply? And what are the conditions to satisfy it?...
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### Reconstruction of sampled band-pass signal

I am pretty new to signal processing. I am currently trying to reconstruct a sampled band-pass signal created with the filtfilt and ...
47 views

### Confused on Pulse Filter Bandwidth, Raw Data Bandwidth and Symbol Rate Relation

Update 30/11/2020 Please can someone help I am confused about the relation between Sinc and Rectangle transform pair and how that relates the Bandwidth of Pulses, Bandwidth of Zero-ISI Filter and the ...
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### How to apply cepstrum coefficient gains (BFCC, MFCC) to an input signal?

I'm trying to understand RNNoise (https://arxiv.org/pdf/1709.08243.pdf, https://github.com/xiph/rnnoise). One aspect in particular, the input signal BFCC coefficients and output signal BFCC ...
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### Is there a systematic method for converting an even length FIR filter to odd length?

I'm currently implementing a discrete wavelet transform (DWT) as a cascaded QMF filter bank (pictured below). I've put together a convolution function that attempts to filter an input signal in a non-...
100 views

### How Come the Low Pass Filter in Sobel Operator Isn't Normalized?

I am relatively new to the field of computer vision and I have just learnt about the sobel operator. The sobel operator in the x direction is a convolution of the finite difference kernel $[1,0,-1]$ ...
32 views

### How can I obtain the transfer function from these two transfer functions in this case?

Using Scipy signal in Python I want to obtain a transfer function for an input which passes first from sys1 and then sys2. So ...
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### Confusion about result of FIR All-pass filter design

I try to design a FIR All-pass filter with random phase in the frequency domain. I am a bit confused by my result and am not sure if the reason is a programming error or a misconception about ...
25 views

### Can you do temporal frequency filtering for a spatially moving signal in image sequence?

Context : A static camera captures video footage of a still indoor environment at given framerate (1080p@30fps or 720p@60fps) A low power line laser projects a line shaped beam in the camera field of ...
33 views

### Phase correction using second order all pass filters/LMS with Wiener-Hopf equations

I am working on phase correction algorithms. Can anyone help me understand how can the following diagram be used for phase correction: Additionally, for a channel function suggested How determine the ...
28 views

### Finding the Correlation Matrix of Wiener Filter using Matlab

I have the problem below and need to solve it using Matlab. I not a big expert in Matlab and just don't know how to implement it. Basically, it says that \begin{equation} R\:=\:\left[X\left(n\right)X^...
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### Matlab FIR filter numerator coefficients to python

I created a equiripple FIR filter in Matlab using filterDesigner and exported it to an ASCII file. The file contains the numerator values as a list of 51 numbers ...
54 views

### Phase of matched filter for chirp signals

I am using the following system: Ultrasonic chirp signals with central frequency 100kHz are being transmitted using ultrasonic sensor. After the transmission through the medium(air/solid/liquid/...
96 views

### High-pass filter with quantized (fixed-point) coefficients

I have a high pass IIR filter with numerator b = [0.997688673703782,-1.995377347407564,0.997688673703782]; and denominator ...
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### Recreating matlab second order filter in python

I want to create some custom filters in Matlab filterDesigner tool and then apply those filters to a large set of audio files. I want to use python to do the ...
42 views

### Lifting scheme versus filter banks

I am having some trouble understanding the intuitive connection between the two. I worked through all the theory and learned that Sweldens showed how to derive lifting steps when having admissible ...
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### How to remove noise from frequency spectrum?

I have a signal acquired at 40 MHz sampling rate, from an ultrasound transducer with center frequency of 5 MHz. The frequency spectrum is shown in attached images (whole spectrum and zoomed). There is ...
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### The Wiener Filter for the Time Derivative of the Signal

Assume the observation of the original signal $s(t)$ is $x(t) = s(t) +n(t)$, where the signal and noise are independent. Then we need to design the Wiener filter $g(t)$ to estimate $\frac{d s(t)}{dt}$ ...
47 views

### Plotting Frequency Response Magnitude and Phase for first order all pass filter

Having trouble plotting the frequency response characteristics for first order all pass filter. The Magnitude is expected to be constant across entire freq and Phase is expected to be only decreasing (...
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### Design FIR with linear phase response

What is the best way to design a FIR filter with a given linear phase response, such that each frequency inside the passband is phase shifted according to: $$H(f)=e^{i2\pi f k}$$ where $k$ is factor ...
52 views

### Why is there a dip in this Chebyshev filter response?

I want to build and simulate a 6 GHz, 4th order lumped-element Chebyshev bandpass filter with a maximum passband ripple of 0.1 dB and a bandwidth of 1 GHz, and as I understand it, there should be 3 ...
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### Apply a Gabor filter to an input image

I tried to apply a Gabor filter with a specific scale (according to my values of lambda and sigma, so it is (7x7) and for 4 orientations (0, $\frac{\pi}{4}$, $\frac{\pi}{2}$ and $\frac{3\pi}{4}$) to a ...
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### How to reduce synthesis artifacts produced by phase vocoder?

I implemented the phase vocoder algorithm in Python to time-stretch speech signals by following this paper and referring to this MATLAB tutorial. I can distinguish words in the original signal from ...
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### 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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### Box function signal filtering in python

I am trying to produce a box function filter of a signal in python. I expected to find this functionality in scipy.signal, but I can't find any solutions. What I am trying to do is this. I have 2 ...
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### Most generally-accepted audio term, for “pre” and “post” lengths of a symmetric filter's impulse response?

Consider a FIR audio filter with symmetric impulse response. In my case, the filter kernel width is 15 frames on each side (so including the center frame, 31 frames total). When examining the audio ...
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### What does poles in unit circles center mean?

Suppose i have all my poles in unit circle center. What kind of information this gives me? Can i determine if this filter is IIR or FIR?
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### Scipy Butterworth highpass filter results in distortion and bloated output

Trying to use Scipy Butterworth filter to filter frequencies below 54 Hz from audio files. Audio files are stored as WAVs. Sample rate is 44100. When I try using this filter the result is distorted (...
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### Need to filter very small signal

I am measuring ECG signals on subjects and I am having issues filtering a very small signal from the inherent noise of the collecting device. I am using an 18 bit ADC to digitize the signal Here is an ...
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### A question about the Commutativity Property in discrete signals block diagrams

According to the Commutativity Property of block diagrams, we can place b0 at the entrance or at the exit of the block diagram, it wouldn't matter. My question is, if we placed it at the entrance, we ...
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### Using MATLAB Function mpiir_l2(): Results Are Not IIR but FIR Filters - Why and How to Avoid This?

I'm using mpiir_l2() from user Matt L's PhD thesis to design IIR filters. I set the number of numerator and denominator coefficients both to the same value (between ...
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### How to design an inverse for a Butterworth low-pass filter?

I have a signal that has a spectral shape very similar to the transfer function of a second-order lowpass filter (butterworth design). I would like to whiten the spectrum of this spectrum in the time ...
3k views

### Is it possible to design noncausal filters in Matlab?

I'm trying to design a lowpass IIR filter with 5Hz cutoff frequency (sample frequency is 200Hz). i know how to create it with fdatool, or with functions such as 'butter' or 'ellip'. However, i think ...
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### Undoing a filter operation in MATLAB

Out of curiosity, is it possible to actually reverse a filtering on MATLAB. For example, if I have ...
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### FIR Filter Type - MATLAB

A question about using fir1/fir2/firpm to design FIR filters in MATLAB. The first parameter is the 'filter order'. For my filter design I pass in 250 as this argument. However, when looking at the ...
117 views

### MATLAB Hamming window

I have been trying to achieve a Hamming window length of 23 using the equation. I tried several coding, one of the is the one below: ...
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### MATLAB $\tt butter$ function

I suspect I have a very basic misconception so I'm trying to clarify that here: A signal should be filtered before it is sampled, correct? That is, I always sample an analogue signal at some sampling ...
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### why difference between this example and matlab result

everyone fs=30 000 , fc=3000; when i code apply this in matlab result is very difference ...
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### Design Filter with Arbitrary Magnitude and Phase Response in Matlab

Does anyone know of a way to design a filter with arbitrary magnitude and phase response in Matlab?
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### Zero-Phase Algorithm in Matlab

From this document it's says 1.Filter the Data 2.Flip that 3.Filter again 4.and Flip that again for zero-phase filter. but when i do this in matlab , i'm compare ...
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### Analytically designing a notch-filter for specified frequency 50 Hz

I tried to analytically construct a causal notch filter that stops frequencies at 50Hz and I thought if zeros are more than poles it will be non-causal so I chose equal amount of poles and zeros ...
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### What is the relationship between poles and system stability?

I see two notions that describe the relationship between poles and system stability. But they are not the same from my understanding The system is BIBO stable if and only if all the poles are in the ...
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### What Is the Bilateral Filter Category: LPF, HPF, BPF or BSF?

I`m reading about Bilateral filter with images, I knew that it uses Gaussian filter (which is a LPF) as a domain filter plus a range filter and it is used to preserve edges(high freq component). Can ...
Reading P. Andrews et al. I see that it is very common to do the following approximation of the process noise covariance matrix: $$Q_{k} = G_{k-1}QG_{k-1}^{T}\Delta t$$ so that the propagation ...