Questions tagged [infinite-impulse-response]

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

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Incorrect Butterworth filter outcome using Rational Transfer Funcion

I've been playing with Second-Order Butterworth high-pass filter for a while. I've calculated the coefficients using Matlab function and I wanted to use them to filter simple sine wave generated by ...
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101 views

Filtering without using any transforms

A composite signal is defined as $$x(t) = \sin(2\pi 10t) + \sin(2\pi 40t) + \sin(2\pi 60t) + \sin(2\pi 50t)$$ Separate the four frequencies without using any of the transform techniques.
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Stable digital filter with leading zeroes

I'm looking construct a stable pole-only filter where the feedback coefficients start with a block of zeroes, i.e. \begin{align} a_0 &= 1\\ a_i &= 0, \textrm{ for}\ 1 \le i \lt k\\ a_i &\...
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168 views

Is initializing a digital filter's output with no “momentum” a non-trivial task?

I'm working on implementing a filter with a very slow step response. This filter is implemented as a cascaded second-order-section filter (transposed direct form 2). I'm using the output of this ...
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3answers
856 views

Is there a common name for the first order IIR averaging filter?

Is there a term to describe this IIR averaging/smoothing filter? $ y[n] = \alpha x[n] + (1 - \alpha) y[n - 1] $
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660 views

Complex IIR to Real IIR

I have created an IIR design algorithm that generates complex coefficients (there is no symmetry in the poles and zeros). However, the IIRs will be used to filter a real signal. Is there a closed form ...
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117 views

Does this equation have a closed form

I am on chapter 6 of "Understanding digital signal processing", 3rd Edition by Richard G. Lyons. But I am stuck on question 6.15. Here is the network in question. I wrote down the difference ...
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1answer
49 views

Audio signal series' beginning points(about 50) distort after a bandpass filter

I am using some bandpass filters to detect a certain freq of the sampled audio series in noisy environment. Everything is OK except this: I found that for many bandpass filters I tried(butterworth, ...
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327 views

Convolution with an impulse response does not give the same result as the frequency response

Context I am trying to design a linear-phase FIR filter with the following frequency and phase responses: Designing the filter Given its characteristics (peak filter at 1kHz with 9dB gain and Q=7), ...
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2answers
580 views

Design a linear-phase FIR filter approximating the magnitude of a given IIR filter

I have a biquad IIR filter from which I want to get a linear-phase FIR. I saw that related question but the OP does not care much about phase. I have troubles getting the exact same magnitude curve ...
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903 views

Whats is the difference between FIR/IIR filters and Chebyshev/Butterworth filters

I am new to Signal Processing. From my understanding -- FIR/IIR just refer to the placement of poles and zeros in the z-domain helping us achieve convolution, if FIR and ??? in IIR. Chebyshev and ...
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85 views

Generic response of an IIR filter from its transfer function

How can I derive the general response of an IIR filter from its transfer function? I know that: $$H(z)=\frac{1}{1+\sum\limits_{m=1}^N{a_m z^{-m}}}$$ Thus: $$Y(z)=X(z)H(z)=\frac{X(z)}{1+\sum\limits_{...
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Typical filter orders

I am on my first DSP project where I want to implement lowpass/highpass filters for ECG application. I have started from MATLAB to give me orders and coefficients for my desired specs. I prefer to go ...
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Digital Filter Design Accuracy [duplicate]

Having only dealt with digital filter scarcely, the question dawned to me when I used the firls function in matlab to design an equalizer with a certain gain response. In general, can we prescribe ...
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1answer
517 views

How to implement a FIR filter with correction of group delay on c#?

I read respect to digital filters, and implemented both IIR and FIR filters and I found that this type of filters have a called "group delay". Now I know that the IIR have a non-linear group delay and ...
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170 views

Fixed point Error Spectrum Shaping (noise shaping) for biquads

Based on that article and all the resources on the internet that advise the use of noise shaping for fixed-point filter implementations, I tried to make a few simulations on Matlab for the biquad I'm ...
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366 views

Converting floating point IIR to fixed point arithmetic, given its difference equation

Is there some general way to perform the task given in the question? I have a filter given as follows: ...
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1answer
225 views

Impulse response of a continuous system sampled with zero-order hold

I've a continuous system $$F(s) = \frac{K}{Ts+1}.$$ I sample it with zero-order hold with sampling period $T_s$. The discrete system transfer function is $$ \begin{aligned} G(z) &= % \frac{z-1}{z}...
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How to design all-pass filter by specifying phase requirements?

I want to delay the part of signal above (or below) specified frequency, but I don't find any books or tutorials to tell how to design is. The commonly used biquad APFs (such as the one introduced in ...
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2answers
717 views

Trouble with fixed-point arithmetic 2nd order IIR implementation in c

DSP newcomer here! I am tinkering around with a TI DSP and am trying to implement a second order IIR filter in C. Input is 16 bit 2's complement, as is the output, the accumulator is 32 bit wide. I ...
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1answer
188 views

IIR filtering vs IFFT filtering by zero binning and making bandpass IIR filters with high sample rates?

I am having some issues making thin IIR filters that work at the sample rate of my data and was wondering if there is a way to improve my method? I am also curious about the deficiencies in using the ...
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560 views

How do scaling of the coefficients for the poles of a biquad filter affect the gain?

Given a digital filter consisting of a chain of digital biquad filters. Given a digital biquad filter with a normalized Direct form 1 difference equation: $ y_n = b_0x_n + b_1x_{n-1}+b_2x_{n-2} - ...
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214 views

Behavior of tanh IIR filters

If we insert a tanh function (or any other activation function) between the feedback summation and the unit delays, how will such an IIR filter behave for values of $|a| < $1 and $a > ±1$ ? The ...
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Memory for FIR and IIR [closed]

I have doubt regarding memory of FIR and IIR, I have read that output of FIR depends upon present and previous inputs, while output of IIR depends upon, present and previous inputs as well as previous ...
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Is there a tool for automatically converting filter implementation forms?

I am looking for alternate tools that will automatically convert filter implementation forms (or signal flow network diagrams in general) to simplest or alternate forms; for example for going between ...
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362 views

Manually Windowing an IIR Filter in Matlab

I am currently trying to window an analog IIR filter in order to obtain an FIR filter. Though I realize the fir1 function exists within Matlab, I was wondering to see if it could be done step-by-step ...
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160 views

Amplitude loss during resampling with IIR

I have a problem in that I am resampling a signal and loosing amplitude. The steps I do are the following, in c++: Upsample/interpolate signal by 16x by padding with zeros. Run an IIR Bessel 2nd ...
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209 views

Software implementation recipe of cascaded Biquad IIR filter

I have been given the task of measuring the performance of Biquad IIR filters on a new CPU that we are evaluating. What I know is that the Biquad filters can be cascaded to form higher order filters. ...
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3answers
441 views

IIR biquad real-time filter just output noises

I've implemented a IIR filter but it outputs only noise (like FM radio out of tuning) and I can't see what's wrong. This is the processing function: ...
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232 views

Simplify equation of single pole IIR transfer function

Example - Consider the causal stable IIR transfer function $$ H(z)=\frac{K}{1-\alpha z^{-1}}, \quad 0 < \lvert \alpha\rvert 1 $$ where $K$ and $\alpha$ are real constants Its square-...
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Appropriate model for IIR filter to compare with spectral ratios

A quick, basic question. I have measured spectral ratios - comparing a measured signal to an 'ideal' signal. I am fitting a specific, simple IIR filter to that data for transfer functions. So, if I'...
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233 views

Analog Filter Prototype to Direct Form Second Order Cascade

I've been using the Faust programming language a lot lately for experimenting with DSP, and I've been digging into their implementation of an Elliptic (Cauer) Lowpass filter. Here's an example of such ...
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289 views

Designing an IIR to generate a specific data sequence

I know that it's possible to design an IIR with specific poles and zeroes to create specific frequency responses. Is it also possible to design an IIR such that when you give it an impulse, it ...
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1answer
641 views

Biquad filter from Matlab to C using “tf2sos”

This is a biquad implementation I use: ...
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1answer
535 views

4th order high-pass filter on a DSP: standard or biquads?

I have two C implementations of 4th order high-pass filter (fs = 16 kHz, cut-off=100 Hz, designed using Matlab ...
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1answer
1k views

If a filter has a non-linear phase lag will the output signal be distorted?

EDIT: From here (https://www.mathworks.com/help/signal/ref/butter.html) it appears that an Butterworth filter has a non-linear phase lag at the normalized frequency of 0.5 onwards. Does that mean that ...
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Filter Order Rule of Thumb

Is there a rule of thumb for calculating the approximate filter order of a FIR/IIR based on passband vs sample rate? I seem to remember reading about it once in Undergrad. I'd think you could make a ...
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985 views

Zero Phase Filter: Determining Initial Conditions for Forward Backward Filtering

Is anybody familiar with Gustafson's algorithm for minimizing transients in forward backward filtering [1]? I'm trying to implement it and my first guess was to check Matlab's filtfilt.m, since they ...
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Problems implementing IIR filter in VHDL

I am having some difficulty making an IIR filter in VHDL work as expected. I have implemented it by shifting the coefficients by a certain number of bits (in this case 27 bits). The outputs are then ...
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1answer
80 views

Implementation of IIR Filter in dsPIC 33EP - Q15

I am implementing an IIR controller in dsPIC 33EP (16-bit, fixed-point, two's complement, wrap-around, 40-bit accumulator, 32-bit multiply, 12-bit ADC) and I am using cascaded, Direct Form I second ...
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2answers
136 views

Is this an infinite response or a finite response?

If you're given $h[n] = 1$ for every even number of $n$, otherwise it'll be 0. Is that considered an infinite response or a finite response and how do you know?
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107 views

Can picking an inappropriate roll-off frequency for a digital filter just alias the roll-off value?

I believe a related question is asked here, but my question deals more with what filter is realized if one fails to consider design parameters relative to sampling rate. In designing an IIR filter we ...
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1answer
250 views

Implementation of IIR Filter in dsPIC 33EP - Scaling

I have to implement an IIR controller in dsPIC 33EP (16-bit, fixed-point, two's complement, wrap-around, 40-bit accumulator, 32-bit multiply, 12-bit ADC) and I am using cascaded, Direct Form I second ...
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1answer
306 views

DSP filter. Is prewarping performed when discretizing using Forward/Backward?

I am trying to derive the coefficients used for a IIR implementation for the lowpass portion of a SVF filter. I've seen finished expressions for the coefficients (smith (p.8) and victor), their ...
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1answer
43 views

While converting discrete filter specs into continuous filter specs, why do we multiply gain by T

As I know so far that when we trying to design a DF(discrete filter) with specific specs "in terms of $\omega$", we take these specs and map it into continuous domain $H(j\Omega)$ using a certain ...
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2answers
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IIR coefficients and difference equation implementation in C language

I can't find anything on this topic, so either I'm in the wrong direction or else there is just nothing about it on the internet. So let's say I have 3 $b_i$ coefficients ($b_0,b_1,$ and $b_2$) and 2 ...
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How does parallel structure implementation of IIR speed up the process ? What happens in case of FIR?

I was learning about digital filter structures and there I came to know that parallel implementation of IIR filters speeds up the process and I understand that.But what I am not convinced of is that ...
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273 views

Filtering everything outside 20 - 20000 Hz

With an audio .wav file (sampled at 44.1 or 96 Khz), I would like to filter out everything outside the 20 - 20000 Hz range. I tried a Butterworth bandpass filter and there were unstability issues, ...
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1answer
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
489 views

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 ...