# Questions tagged [infinite-impulse-response]

Infinite impulse response (IIR) is a property of signal processing systems.

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### Digital Filters

If I want to remove the baseline drift in my ECG signal, which digital filter should be used without distortion and shift in my filtered output? What are the necessary things I have to look for the ...
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### Reconstructing input from the output of a known discrete-time IIR filter

I have known discrete-time IIR filter. I pass a signal x(n) through the filter and obtain the output y(n). How would I design a filter to obtain x(n) from y(n)? In general, is it possible to design ...
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### How to check if a signal is mainly composed of a few impulse peaks?

I am working on a problem that produces different types signals, and I need to detect the peaks after low-pass filtering, then find_peaks from ...
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### Output power of a signal passing through an IIR filter

suppose I have the following discrete time signal $x\left(n\right)=0.7\sin\left(2\pi \times 623\:nT\right)$ where $N=4000$ and $T=\frac{1}{f_s}$, where $f_s=40$ kHz I pass this signal through a simple ...
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### IIR implementation - RuntimeWarning: overflow encountered in double_scalars [closed]

I have implemented a butter filter in python using this function: ...
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### What is difference between “Direct form” and “Normal Direct form”?

What is difference between "Direct form" and "Normal Direct form"? I was reading about filters implementations(structures) and found out both words "direct form"and "...
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### How to apply the gain factor G to SOS coefficients when designing a IIR filter on sptool (MATLAB)?

After designing an IIR filter on sptool, I export the coefficients (SOS) and gain (G) into a .mat file. When filtering, we can use sosfilt(SOS, x), which results in the correct output but with the ...
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### Recursive, non-recursive systems; FIR, IIR systems

I am confused with the classifications of an LTI system as recursive or non-recursive systems and FIR or IIR systems. I understood what the FIR and an IIR systems are, but is it correct to say that ...
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### Practical IIR filter implementation

I'm trying to implement a digital IIR filter on an FPGA and would be happy for some inputs regarding the actual digital implementation. I don't have a lot of experience with FPGAs and digital filters ...
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### How to implement a high pass filter digitally to remove the dc offset from sensor data

I'm trying to implement a high pass filter on sensor data to remove the dc offset. I'm aware I can subtract the mean of the data but I'm looking for a frequency domain approach. I've used the matlab's ...
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### Implementing an IIR filter in Pytorch using RNN with no nonlinearity

Is it possible to implement an RNN layer with no nonlinearity in Pytorch like in Keras where one can set the activation to linear? By removing the nonlinearlity, I want to implement a first-order ...
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### Digital lowpass filter causing aliasing

I'm writing a biquad filter program in C++, using the LBJ Cookbook as the source for the formulas. https://webaudio.github.io/Audio-EQ-Cookbook/audio-eq-cookbook.html The lowpass filter that I've made ...
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### IIR initial condition / state meaning

I am studying filters, in particular the Infinite Impulse Response ones. I digged into theory and practice and I gain some decent knowledge on the topic. However, I can't really figure out or find ...
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### How to find Cutoff frequencies (f1 &f2) for a narrow band pass filter for a particular central frequency?

This is a basic filter question I think. I want to define a narrow bandpass filter's cutoff frequencies (f1 & f2) for a particular central frequency (fc) in iir filter I think in this case ...
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### Does my filter desing for unusual EEG experiment looks good?

I have made some progress since my last question, and again I am asking you for advice. Hi, I'm still designing an unusual (in terms of signal analysis) EEG experiment, which forces me to design my ...
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### What is the relationship between group delay and propagation delay for a filter? [duplicate]

I was trying to design a filter for a system and I was able to obtain the group delay plot in matlab using grpdelay. The group delay output is in samples. However, I was not able to relate that data ...
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### Matlab group delay not corresponding to reality

I studying effects of digital filters group delay (IIR). In Matlab there is a function grpdelay which allows for particular frequency get a value of delay in samples But after filter applying and ...
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### trying to reproduce the behavior of initial conditions for the filter delays of scipy lfilter with R

I'm trying to reproduce the behavior of lfilter and lfilter_zi (from scipy) in R (using signal package if possible). This is the example provided by ...
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### Stability of filters with negative phase delay, group delay, and positive phase

Lets assume I have an IIR filter with : bz = [1.0195 0 0]; az = [1 0.0166 0.0020]; fvtool(bz,az) The filter is stable as i can see. If you check the phase delay ...
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### Impulse Response for an Anti Causal Linear Shift Invariant System

I have a system given by $$y[n] - \frac{1}{4} y[n-1] - \frac{1}{8} y[n-2] =3x[n]$$ I'm asked to determine the impulse response of both an anti-causal and a causal Linear Shift Invariant System ...
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### How to design IIR digital filters

Practical Infinite-Impulse-Response (IIR) filters are usually based upon analogue equivalents (Butterworth, Chebyshev, etc.), using a transformation known as the bilinear transformation which maps the ...
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### Stopband's edges in bandpass IIR filter in MATLAB

I've tried to get an IIR bandpass filter having the passband [0.1,0.5] Hz and working at the sampling frequency 8 Hz using the following command: ...
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### What are the equations for magnitude plots of the common IIR filters? (Are the ones I have so far correct?)

I need equations that describe the magnitude plots of basic IIR filter types. I had looked into this a few years ago and saved some equations but it only covers part of what I need, and I can't recall ...
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### Is there an equation that will graph the shape or predict the maximum amplitude of a single sample impulse fed through a One-Pole LPF?

If you feed a single sample impulse of a given amplitude through a One-Pole LPF you get an envelope that looks like this: The output of the LPF from its peak will settle into an exponential decay ...
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### what is purpose of IIR filter? [duplicate]

I am working on Digital Signal Processing. I know theory very well but I don't understand why IIR filter is used in place of FIR. What is advantage?
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### Summation of two IIR filters

Actually my question is how to get the weighted average of two or three IIR filters given their transfer functions, which is nearly equal to this question. How to calculate the total transfer function ...
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### 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 ...
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### When is the sum of two (parallel) minimum-phase filters also minimum-phase?

Say I have two minimum-phase filters: $$\frac{A(z)}{B(z)} \: \text{ and } \: \frac{C(z)}{D(z)}$$ That is, the roots of $A(z)$, $B(z)$, $C(z)$ and $D(z)$ are all in the stable region. If add them ...
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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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### Approximation and IIR Filters

Consider the discrete-time time-invariant system with input $x[n]$ and output $y[n]$ satisfying $$y[n] = \sum_{k=1}^5{x[n-k]}$$ Consider approximating the desired system with a second-order IIR system ...
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### How to practically correct for group delay imposed by a digital filter (Python)

I'm using Python to filter a signal using a Butterworth filter (scipy.signal.butter) and subsequently passing this through a forward-backward filter with cascaded second order sections (scipy.signal....
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### Frequency response of a digital state variable (Chamberlin) filter

I recently implemented a digital state filter based on the recommendation here. I've tested this filter's performance as a very low cutoff low-pass filter with limited coefficient quantization ...
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### Mitigate floating-point numerical errors for very-low corner frequency low-pass filter with DSP

I'm designing a low-pass filter for a digital signal processing application that ideally just passes a very small bandwidth above DC. I'm using an IIR biquad filter for this, where the coefficients ...
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### What is the purpose of the recurrence relation in low and high pass (audio) filters?

Newbie here. I'm familiar with time and frequency domains from math. I think I understand what low and high pass filters do, sonically. But digging into an implementation of ...
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### Why does Pre-warping work with a notch filter but not a low pass filter?

Hey guys a little bit of a continuation from a previous post I made here, I found the solution as why the pre-warping was not working at the time, However I was just playing around and found out pre ...
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### IIR filter relationship between number of poles, order and second order sections

I have ported Iowa Hills Code Kit to a mcu to calculate IIR filter coefficients. They are used to initialize the CMSIS Biquad Cascade IIR Filters Using a Direct Form II Transposed Structure. Trying to ...
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### Are IIR filters (and specifically Butterworth filter) causal?

I am new to signal processing. I am learning now about filtering and I am trying to implement high pass filter (HPF),and later band-pass filter (BPF). I implement the filters in ...
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### What is the best way(In terms of speed) to implement a direct form type 2 IIR Filter in VHDL?

I am trying to implement a 4th order direct form type II IIR filter in VHDL(Specifically, in xilinx FPGA) and when i implement it i get correct output yet very low maximum clock rate(Around 80 Mhz). ...
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### IIR bandpass filter with very low corner frequencies

I'm trying to get in the MATLAB Signal Processing Toolbox a bandpass IIR filter having the following specifications: pass-band [0.1-0.5] Hz and stop-band attenuation 30 dB. I'm using the following ...
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Following shows the discrete time Fourier transform of an ideal low pass filter with cutoff frequency $\omega_c$: H\left(e^{j\omega}\right) = \begin{cases} 1, & \text{if $|\omega| \le \omega_c$...
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### Notch filter: differences between IIR and FIR filters

I'm trying to understand this great answer from Matt L. . It's said that "One advantage of IIR filters is that steep filters with high stopband attenuation can be realized with much fewer ...
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### How do software equalizers work?

Recently, I have been studying IIR and FIR filters, and trying to create a parametric equalizer using a microcontroller. More specifically, I use the ADC on it to sample the audio at about 44 kHz, and ...
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### 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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### Calculation of gain at certain frequency in case of nth order IIR filter

There is this method for to set 0dB gain to be at wanted frequency (fc) (Octave/Matlab example for biquad LPF): ...