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# Questions tagged [infinite-impulse-response]

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

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### 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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The uncertainty principle is usually stated as a relationship between a continuous signal and that signal's Fourier transform, and says that $$\int_{-\infty}^{\infty} \! x^2 f(x) \ \mathrm{dx} \int_{-... 2answers 1k views ### Step response overshoot in IIR filters Is there an analytic expression by which it is possible to calculate overshoot of step-response of second order IIR digital filter? I have tried to search through Mitra's signal processing book and ... 1answer 1k views ### DC blocking IIR filter clipping? I'm processing audio data for voice input from a mic. The data arrives in 32 bit floats [-1 ~ +1]. My first filter is to remove DC: ... 2answers 3k views ### Hilbert transform filter for audio applications: Using IIR half-band parallel all pass structure Does anyone have any experience designing wideband IIR Hilbert transform filters with audio applications in mind? I am using the filter for single side band modulation audio effects discussed in this ... 2answers 40k views ### Filter order vs number of taps vs number of coefficients I'm learning DSP slowly and trying to wrap my head around some terminology: Question 1: Suppose I have the following filter difference equation:$$y[n] = 2 x[n] + 4 x[n-2] + 6 x[n-3] + 8 x[n-4]$$... 2answers 619 views ### IIR Filter structure implementation dynamic range I want to implement an IIR filter. The filter is going to implement by cascading second order sections. Below there are 3 pictures that implement this filter using: Denominator - Numerator using ... 2answers 1k views ### Pole-Zero Plots Diagram Explanation I experiment with the coefficient quantization in an IIR filter. I change some values like the passband ripple and also how many bits i want for the quantization method. In the first picture i have ... 3answers 6k views ### How to find the group delay of IIR filters in Python/SciPy I sent a square wave signal (red) through a IIR filter (butterworth in this case), to make it more "realistic". Then there's a slight group delay in my output signal (blue). Is there a way to find out ... 2answers 2k views ### IIR Filter for Smoothing (Low Pass Filter) I am using IIR filter for smoothing$$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 ... 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 ... 5answers 8k views ### 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 ... 1answer 3k views ### 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 ... 3answers 2k views ### 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 ... 1answer 5k views ### 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 ... 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 ... 1answer 2k views ### 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 ... 2answers 1k views ### 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 ... 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 ... 1answer 3k views ### 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 ... 5answers 1k views ### 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] $$The architecture that I'm using has access ... 2answers 6k views ### How does MATLAB handle IIR filters? MATLAB has a butter, which constructs a Butterworth filter given an order and relative cutoff frequency. The filter created can be used to ... 3answers 3k views ### Downsampling lowpass filter for audio: FIR or IIR? I'm working on a real-time audio processing project in which I have to downsample a 44.1 kHz to a yet-to-be-determined lower sampling rate essentially for reducing computational complexity. I'm ... 5answers 15k views ### What Is the Best First Order IIR (AR Filter) Approximation to a Moving Average Filter (FIR Filter)? Assume the following first order IIR Filter:$$ 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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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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### 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 ...