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Questions tagged [infinite-impulse-response]

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

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1answer
5k views

Digital filter design basic principles (IIR/FIR)

Although I have a solid experience in designing audio engines and such, I am fairly new to the realm of Digital Filter Design, particularly IIR and FIR filters. In other words, I'm trying to learn as ...
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2answers
322 views

What does the uncertainty principle say about recursive filters?

The uncertainty principle is usually stated as a relationship between a continuous signal and that signal's Fourier transform, and says that $$ \int_{-\infty}^{\infty} \! x^2 f(x) \ \mathrm{dx} \int_{-...
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Step response overshoot in IIR filters

Is there an analytic expression by which it is possible to calculate overshoot of step-response of second order IIR digital filter? I have tried to search through Mitra's signal processing book and ...
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1answer
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DC blocking IIR filter clipping?

I'm processing audio data for voice input from a mic. The data arrives in 32 bit floats [-1 ~ +1]. My first filter is to remove DC: ...
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2answers
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Hilbert transform filter for audio applications: Using IIR half-band parallel all pass structure

Does anyone have any experience designing wideband IIR Hilbert transform filters with audio applications in mind? I am using the filter for single side band modulation audio effects discussed in this ...
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2answers
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Filter order vs number of taps vs number of coefficients

I'm learning DSP slowly and trying to wrap my head around some terminology: Question 1: Suppose I have the following filter difference equation: $$y[n] = 2 x[n] + 4 x[n-2] + 6 x[n-3] + 8 x[n-4]$$ ...
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2answers
619 views

IIR Filter structure implementation dynamic range

I want to implement an IIR filter. The filter is going to implement by cascading second order sections. Below there are 3 pictures that implement this filter using: Denominator - Numerator using ...
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2answers
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Pole-Zero Plots Diagram Explanation

I experiment with the coefficient quantization in an IIR filter. I change some values like the passband ripple and also how many bits i want for the quantization method. In the first picture i have ...
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3answers
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How to find the group delay of IIR filters in Python/SciPy

I sent a square wave signal (red) through a IIR filter (butterworth in this case), to make it more "realistic". Then there's a slight group delay in my output signal (blue). Is there a way to find out ...
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2answers
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IIR Filter for Smoothing (Low Pass Filter)

I am using IIR filter for smoothing $$y[n] = ax[n]+(1-a)y[n-1]$$ My question is, if I add another IIR filter, will it be the second order of IIR filter? If not, what it can be called? My second ...
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1answer
486 views

IIR filter design in digital domain using the magnitude squared

Does anyone have any good references for deriving parameters of an IIR Low pass/High Pass filter directly in the digital domain using the magnitude squared at the corner frequency? I have been able ...
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5answers
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What is the exact meaning of unstable system in DSP?

In physical systems I understand what is the meaning of stability or unstability. An operational amplifier for example, if working in positive feedback will either saturate or start osscilating (i.e ...
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1answer
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IIR filter design in matlab

I have to design 2 IIR bandpass filter with the following specifications: Sampling frequency 1000 Hz Pass-band 50 Hz to 200 Hz Order 6 using bilinear transform and impulse invariance with Butterworth ...
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3answers
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Why is the gain of my IIR filter positive?

Sorry, two questions in one day! I'm struggling to understand what I'm doing wrong in this very simple filter design. I want to design a simple, single pole low pass filter and implement it as an IIR ...
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1answer
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Pre-emphasis / De-emphasis filter design

I've designed a simple FM communication system and found that high-frequency noise is a real problem. It appears that this is a well known issue, which has been solved through pre-emphasis of high ...
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2answers
951 views

complementary IIR filters

I would like a pair of complementary IIR filters (lowpass/highpass). By complementary, I mean, when the output from the two filters is summed, the original signal is recovered. I thought I could build ...
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1answer
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Do FFT-based filtering methods add intrinsic latency to a real time algorithm?

In a current audio processing application, I am working entirely in the time domain using IIR filters. This is so I can use an audio buffer of just 3 or 4 samples and can guarantee that there will be ...
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2answers
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What bandpass filter design will yield the shortest impulse response?

Designing a simple 2nd order IIR bandpass Buterworth filter with a centre frequency of 500 Hz and a 1 octave bandwidth gives me the following frequency response ... Now, if I take the impulse ...
2
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1answer
610 views

Sliding DFT: I think my results are accurate, but I can't buy a swap-swap IDFT

I've got a sliding DFT implementation that appears to be working (judging from an output plot). I would like to be able to invert this implementation using the standard tricks of swapping the real and ...
7
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1answer
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Realtime fixed point IIR filter implementation in C

I would like to implement a fourth order fixed point low-pass IIR filter in C (with Q15 arithmetic), and I will prepare this filter by using two stages cascaded direct form-II bi-quad filters. I have ...
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5answers
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How can I vectorize the computations for a first-order recursive filter?

I have a simple single pole low pass filter (for parameter smoothing) that can be explained by the following formula: $$ y[n] = (1-a) y[n-1] + a x[n] $$ The architecture that I'm using has access ...
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2answers
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How does MATLAB handle IIR filters?

MATLAB has a butter, which constructs a Butterworth filter given an order and relative cutoff frequency. The filter created can be used to ...
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3answers
3k views

Downsampling lowpass filter for audio: FIR or IIR?

I'm working on a real-time audio processing project in which I have to downsample a 44.1 kHz to a yet-to-be-determined lower sampling rate essentially for reducing computational complexity. I'm ...
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5answers
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What Is the Best First Order IIR (AR Filter) Approximation to a Moving Average Filter (FIR Filter)?

Assume the following first order IIR Filter: $$ y[n] = \alpha x[n] + (1 - \alpha) y[n - 1] $$ How can I choose the parameter $ \alpha $ s.t. the IIR approximates as good as possible the FIR which is ...
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3answers
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How does cascading biquad sections for higher order filters work?

I'm trying to implement an 8th order IIR filter and every application note and textbook I've read says that it is best to implement any filter of order more than 2 as second order sections. I used <...
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3answers
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How can I design a very narrow filter?

Suppose I've got an audio signal sampled at $48000$ Hz, and I'd like to design a low-pass filter that isolates everything below ~$60$Hz. In the digital world, this is a low-pass filter with the ...
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2answers
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Are there any standard implementation forms for tunable Butterworth filters?

One of the standard ways to implement a Butterworth filter is with a cascade of second-order sections, each corresponding to a pair of complex-conjugate poles. For a fourth-order filter, for example, ...
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5answers
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What factors should I consider when choosing an IIR filter realization?

IIR filters may be implemented as direct form 1 or 2. But how do you decide which form to use? What are the pros and cons of each?