Questions tagged [infinite-impulse-response]

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

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388 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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2answers
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Find reverse one pole lowpass filter

I need to find a filter that revert the one pole filter of the current signal, a function using Python (or MATLAB) scipy.signal.filtfilt or ...
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332 views

How to obtain digital IIR filter coefficients for known z-plane zero-pole plot?

My clue is just to expand brackets and obtain coefficients of numerator and denominator of my transfer function. Am I right?
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6answers
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Design of a digital A-weighting filter with arbitrary sample rate

I want to A-weight a time series with arbitrary sample rate. An analog A-weighting filter is defined exactly by IEC 61672-1. But there's no definition for a digital filter. One method is to use the ...
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566 views

advantage of using impulse response function for LTI systems? [duplicate]

i have a discrete-time LTI system $L$ that takes input signal $x[n]$ and gives the output signal $y[n]$. since $L$ is LTI, $y[n]$ can be derived as a sum of shifted and scaled impulse responses of $L$....
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What's the point of MATLAB's scaling array for secord-order-section filters?

I'm currently working on a project where I'm implementing different filter types (e.g. iirs - direct form 1, 2, transposed 1, 2, etc.). I just recently started attempting to implement a second order ...
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78 views

IIR with asymptotic impulse response

I have plot some of the IIR filter's impulse responses and some of them are exponentially increasing, increasing, decreasing etc but some IIR's impulse response approaches 0. If for example I have an ...
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1answer
202 views

Are circular buffers relevant to transposed direct form IIR filters?

I'm currently working on a project where I'm programming IIR digital filters. I have already finished the direct form 1 and & 2 implementations. When doing direct form 1 and 2, I was able to ...
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1answer
538 views

DFT in IIR filters

To further summarize, I want to create a function in matlab that finds the time domain signal $y(n)$ and its $n$ time components ($n=0,1,2,...$) given the numerator and denominator of a transfer ...
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3answers
2k views

Is there a way to derive an FIR filter using an IIR filter?

I know there's a thread similar to this one here, but the OP is asking the reverse of what I'm trying to find here. I've done some research on the web with very few sources coming up with actual ...
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2answers
225 views

Implementation of a filter in a software application

I have to embed a bandpass filter into a software application. All the signal processing will be done in 32 or 64-bit double precision. The filter coefficients for an IIR Butterworth filter are ...
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1answer
121 views

Starting off an IIR with plain averages to accelerate slow rise time

A 1-term IIR can easily be started off with the first data point, instead of 0. For data that's all > 0, this ought to be better than starting off with y = 0 : <...
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1answer
223 views

Two question about RBJ Peak filter

I'm new into DSP and Filters in general. Its the first step ahead I do from learning and using a 1-pole IIR basic Low Pass Filter. I'm about to implement for my VST audio application (using C++ and ...
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1answer
429 views

Force an unstable IIR filter to be stable by forcing a nonlinearity in the digital block diagram

I am modeling an analog filter with digital software and have reduced the model to a 4th order FIR filter in discrete space with transfer function $$ H(z) = \frac{b_0 + b_1 z^{-1} + b_2 z^{-2} + b_3 ...
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1answer
3k views

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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3answers
5k views

How to read Phase response graph?

I'm a noob on DSP in general. But I'd like to understand this graph. It is the phase response of a band-stop filter, from Wikipedia: I get the magnitude graph above: at some frequencies, the gain go ...
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Frequency Domain Filtering

Can you create a zero phase IIR filter by transforming its impulse response into frequency domain and only taking the magnitude of that frequency repsone? I have seen this in an open source project ...
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Optimizing Two Parallel IIR Filter Sweeps

Got an audio related question here; So I have two IIR low pass filters that work in parallel to do a filter sweep. Basically: ...
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1answer
294 views

Design Stable IIR Filter in MATLAB

I need to design a stable IIR filter in MATLAB. Specifically, I am trying to use a butterworth filter to correct the phase and gain of a 2 pole RC filter: ...
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3answers
154 views

Removal of gradually-increasing dc component (offline, zero-phase)

A program I'm writing produces a signal with a dc component that increases over time. I need some kind of post-process which can remove the dc content, without affecting the phase or magnitude of the ...
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4answers
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Higher-order (Butterworth) filters

This is a general question, I am just trying to understand the concept. Why should we use higher-order filters, other than a 1st order (of any type for that matter, but we can keep the discussion to ...
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1answer
237 views

Architecture for high sample-rate FIR/IIR filter on FPGA or ASIC?

Assume we have a hardware (FPGA or ASIC) which can operate at a fixed processing frequency of $100\textrm{ MHz}$. Assume we have an input data stream of $1\textrm{GSPS}$ (which has been sampled using ...
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1answer
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How does this “simple filter” work?

I'm new to DSP, and I'm using this basic "1-pole LPF" Param Smooth filter which "smooth" param when I change it. The code is pretty simple: ...
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2answers
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Trying to identify the best method for IIR realizations

I'm relatively new to implementing IIR filters in raw programming formats (i.e. C or C++) and I've run into the concept of IIR filter realizations. So my question: is there a 'best format (works 99% ...
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1answer
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Why is there little emphasis on phase distortion?

I have a question regarding the frequency response of digital filters. Specifically the phase aspect of the frequency response. Why do we not seem to care about the nonlinear phase response in ...
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1answer
133 views

Why is the frequency response different based on the amplitude of the impulse I feed into the filter?

I am working on a 2-pole IIR high-pass filter. The filter is fixed point and it is causing me some issues. I believe I'm just misunderstanding something. I am implementing everything in Octave for ...
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159 views

Sound glitches using fft segmented convolution

I’m trying to build a binaural audio player, I'm using MIT Kemar c library to get the hrtf and a fft segmented convolution. It works on real time but the problem is each time I change the hrtf I hear ...
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1answer
433 views

Generating blue/violet noise without FFT

I need noise with a high frequency bias for a realtime audio application, so I'm interested in things like blue noise or violet noise. Is there a way to generate such noise without using a FFT or an ...
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What's the advantage of adaptive IIR filter against FIR?

Adaptive IIR filters is not straightforward, and may be unstable. Many people say that adaptive IIR filters use less coefficients than FIR filters. What I'm curious about is how many coefficients can ...
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2answers
204 views

Learning about inverse-z-transform and how to apply it to a rational transfer function

I have been studying IIR filters and know that a rational transfer function: $$ H(z) = \frac {b_0 + b_1 z^{-1} + ... + b_N z^{-N}}{1 + a_1 z^{-1} + ... + a_N z^{-N}} $$ has a finite difference ...
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1answer
232 views

How do I test stability of a MIMO system?

Let's say I have a system similar to two interconnected IIR filters described like this: \begin{align} x_1(t)&=a_{11} x_1(t-1)+a_{12} x_1(t-2) +a_{13} x_2(t-1) + a_{14} x_2(t-2)+y_1(t)\\ x_2(t)&...
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1answer
271 views

Weighting function for output error IIR filter design

I noticed, when I try to fit filter coefficients to a given complex transfer function with the output error method, implemented for example in the MATLAB function ...
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1answer
791 views

Causal and Non-causal filtering. Strange behavior

I'm trying to understand the behavior of a causal filtering exemplified by figure below. This behavior is making LDA (Linear Discriminant Analysis) misclassify our data, by clearly reverse the signal ...
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612 views

Is there a method to calculate the maximum gain of a biquad?

Given an IIR expressed as a biquad: $$ H(z) = {b_0 + b_1 z^{-1} + b_2 z^{-2} \over 1 + a_1 z^{-1} + a_2 z^{-2}} $$ Is there a way to calculate the maximum gain the biquad attains over the range $0$ ...
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281 views

Difference equation when transfer function expressed as poles and zeros

The transfer function $H(z)$: $$ H(z) = \frac{Y(z)}{X(z)} = \frac {b_0 + b_1 z^{-1} + b_2 z^{-2}} {1 + a_1 z^{-1} + a_2 z^{-2}} \tag{1} $$ Has difference equation: $$ y[n] = b_0 x[n] + b_1 x[n-1] + ...
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2answers
177 views

Impulse response of a continuous time system

Question The impulse response of a continuous time system is $h(t) = e^{-t}u(t)$. When $x(t) = u(t - 1)$ is input to this system what is the value of the output signal $y(t)$ at $t = 2.34$. My ...
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2answers
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Formula for Bessel low-pass filter coefficients

When I am filtering a signal in python, it has a built in function to generate bessel filter coefficients given a cutoff ratio and a filter order (number of poles). I am trying to translate this to C ...
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2answers
174 views

Analytical way to generate an IIR that is the square root response of another IIR

For simplicity take the transfer function of a second order IIR in $z$-domain: $$ H(z) = \frac {b_0 + b_1 z^{-1} + b_2 z^{-2}} {a_0 + a_1 z^{-1} + a_2 z^{-2}} $$ Is it possible to generate a new ...
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1answer
400 views

Real Time Goertzel Algorithm

Why is Goertzel Algorithm considered a block algorithm? Given that my input is bounded, couldn't I just run it forever (taking every sample that comes out after some length N) given a big enough word ...
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1answer
145 views

Shall a $1^{\rm st}$ order IIR filter include $x[n-1]$ term?

I have seen a $1^{\rm st}$ order IIR filter in the following form: $$y[n] = \alpha x[n] + (1 - \alpha) y[n - 1]$$ Such as: another post in this forum However, the filters generated by Matlab, such ...
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Comparing with FIR, why does IIR always gives a bias error, when calculating signal DC?

I am trying the DC blocking function in matlab. The algorithm of DC blocking is to find DC of the signal first and then remove the DC value from the signals. Here are the codes I tried, which are ...
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1answer
473 views

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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3answers
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How to design very narrow, sharp lowpass filters - Only DC needed?

I asked exact the same here one year ago: One year ago question I asked this question again here, because after one year, I have learned more about DSP and am thinking ways to improve it. Filter ...
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1answer
441 views

Correcting Impulse Invariance Method

I'm trying to find out if the correction (Jackson, Nelatury, Mecklenbräuker) could improve the (IIM based) filter response near Nyqvist. Here's my c++ routine (which is used for to calculate various ...
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2answers
354 views

Unexpected behaviour when using lfilter with initial filter delay multiple times

I want to filter a very long signal in smaller parts, therefor I am currently using scipys lfilter with an initial filter delay doing multiple iterations of: <...
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1answer
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Fitting an IIR filter to a complex transfer function

anybody knows of better ways to fit an IIR filter to a complex transfer function than Matlab's invfreqz.m? I'm implementing a little transfer function fitting ...
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0answers
295 views

IIR filters with variable roll-off

I have a filter design problem in which lowpass filters have to be designed with varying roll-off. E.g: 2.7 db/ocatve or 1.4 db/ocave. See picture below. This is easy to achieve with a FIR filter, ...
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1answer
221 views

Phaser effect with feedback control IIR filter calculation

This question is possibly relevant to this one, but it's not duplicate as far as I'm aware. I'm trying to make phaser with feedback control as shown in the picture below: (Got it from here) First ...
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1answer
71 views

Differentials - Differences: Non causality in the system

I'm still learning DSP and referring to Oppenheim video lectures. In that lectures, differential difference equation is obtained for IIR filter design, in Lecture 14. $$\mathcal{L}[\frac{\mathrm d}{\...
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1answer
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IDFT of H(z) sampled in N values

If a have a causal IIR filter described by $H(z)$ and I sample it in $N$ equispaced values around the unit circle, I get a DFT of $N$ points. That DFT corresponds to $h[n]$ truncated in $n=N-1$ or to ...

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