Questions tagged [infinite-impulse-response]
Infinite impulse response (IIR) is a property of signal processing systems.
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1answer
34 views
Single-pole IIR low-pass filter - which is the correct formula for the decay coefficient?
A single-pole IIR low-pass filter can be defined in discrete time as y += a * (x - y), where y is the output sample, ...
0
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1answer
29 views
What is zero-phase filtering and forward-backward filtering?
I am pretty familiar with IIR and FIR filtering and I have implemented them in my several projects. However, recently i found something called zero phase filtering. I have tried to understand it but ...
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1answer
71 views
Orders of complimentary butterworth filters for IMU
I'm currently trying to design a complimentary filter for deployment on a drone, as part of an assessed semester project. Even though processing power is not an issue (we have GHz, lots of pipelining ...
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2answers
31 views
Why using the impulse respond of an LTI to characterize its output?
We all know that every LTI, is defined by its transfer function, so we can determine the output of any system, (using common transforms). It is also known that we can determine the output of any LTI ...
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1answer
31 views
How do I add more resolution / taps to an analog -> digital filter?
(I am trying to create an IIR audio filter that adds reverb to an initial sample)
Say I designed an analog filter to model acoustic attenuation based on the following mathematical model:
$$
I = I_0 ...
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1answer
63 views
mpiir_l2(): Results are not IIR but FIR filters - why and how to avoid this?
I'm using mpiir_l2() from user Matt L's PhD thesis to design IIR filters. I set the number of numerator and denominator coefficients both to the same value (between ...
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2answers
55 views
IIR high pass filter
I'm trying implement an IIR filter. I know the IIR filter come from that equation:
and i found that for high pass filter the coefficients are:
where fc = cut freq.
here my matlab code:
...
1
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1answer
39 views
iir biquad filter not working
I am trying to implement a butterworth bandpass filter
My filter requirement is Fs= 500Hz, Fc1=0.4Hz, Fc2=4Hz, Oreder=2.
Below is the code which is implemented on 16bit-mcu and is called for every ...
4
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2answers
49 views
references for techniques to reduce recursive filter startup transients
I am trying to track down references (published articles or reports ideally) that establish the basis for some of the techniques being used to minimize the effect of recursive digital filter startup ...
1
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1answer
46 views
VHDL fixed point implementation of IIR filter
I have a filter described by the following transfer function H(z):
$$H(z) = \frac{156 - 156z^{-2}}{16384 - 32443z^{-1}+16073z^{-2}}$$
How will this be implemented with the first term in the ...
0
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1answer
76 views
How to find the impulse response of this system with complex roots?
I've been working trying to analyze a causal stable system. Hopefully a numeric example such as the one I am working on, and the problems I face during it could be useful to others.
I have this ...
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2answers
87 views
How to compare many bandpass filters (for their signal propogation delay)?
Let's say we have an audio signal sampled at 96 kHz, and we want to compare several bandpass filters to find the one with the lowest rectangular-envelope-propagation-delay (see graph below).
The band ...
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1answer
41 views
How does an IIR system affect magnitude and phase of a sinusoidal signal
Consider an IIR system with impulse response $h[n]=\left( \frac{1}{\sqrt{3}} \right)^n u[n]$. If I apply $x[n]=\cos(n \frac{\pi}{2} + \varphi)$ at the input, how can I determine the change in ...
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0answers
44 views
What happens to a rectangular signal filtered with an Exponential Smoothing filter?
Filter given; $y[n] = \alpha x[n] + (1-\alpha) y[n-1]$.
In principle all samples before the present one influence
What happens to a rect-signal? How would it look like?
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2answers
59 views
How can I convert a step response that is described by the sum of two exponents to an IIR filter analytically?
If a system has the following step response:
$$\begin{align}
y(t) &= 1 - \Big(A e^{−t/T_1} + (1-A) e^{−t/T_2}\Big) \\
&= 1 - A e^{−t/T_1} - (1-A) e^{−t/T_2} \\
\end{align}$$
and I know the ...
5
votes
4answers
463 views
Why is the first value in digital first-order IIR filter impulse response not the largest?
When I create a digital first-order IIR low-pass filter with scipy (code below), I get the following coefficients:
B: [ 0.1367 0.1367]
A: [ 1. -0.7265]
The ...
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2answers
60 views
Calculating a NRR of an IIR
I'd like to calculate the Noise Reduction Ratio of a system.
The system I have is $$ H(z)= \frac{z^{-5}}{1-0.1z^-1}.$$
For FIR Filters this can easily done by $$ \sum h[n].$$
For an IIR Filter this ...
4
votes
1answer
148 views
Advancing a causal IIR filter's impulse response
Given an infinite impulse response (IIR) filter as coefficients in a topology of your choice, what is a straightforward way to modify the filter so that the impulse response is shifted in time (...
0
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1answer
46 views
Simple question about Sinc()
Suppose I use the ideal lowpass filter eq to attempt creating a IIR filter using it
:
$$
h[n] = \frac{\sin(\omega_c \, n)}{\pi \, n}, \qquad -\infty < n < \infty
$$
Obviously, I can't really (...
5
votes
6answers
202 views
Optimal $ n $ -th Order IIR /AR Approximation of a Moving Average Filter
I would like to approximate a moving average filter with an IIR filter of much lower order than the tap-length of the moving average filter. Optimality shall refer to the $L_2$ norm of the impulse ...
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1answer
45 views
Design digital filter with model order reduction (MOR) and other methods
IIR filters can be designed using different methods,such as:
Analog Prototyping
Direct Design
Generalized Butterworth Design
Parametric Modeling
https://www.mathworks.com/help/signal/ug/iir-filter-...
2
votes
1answer
47 views
How would I calculate the state-variables of digital biquad filter (direct form II transposed) at steady-state?
I'm attempting to calculate the steady-state state variables for a digital biquad filter direct form II (transposed). Illustration
For example, let assume the filter is fed a constant input of ...
-2
votes
2answers
43 views
How do you initialize the output of a second-order-section filter?
I've got a 4 stage second-order-section filter. When I turn this filter on, it assumes it is starting from zero and takes forever to converge on the actual signal.
For example, let's say I have a ...
0
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1answer
62 views
Question of Digital filter; stability and order
Below 1~6 are my question.
Shortcomings of IIR filter.
Mean of unstable. (Things that will happen when system is unstable.)
How to select the best order(n).
What happens when I raise order too much.
...
1
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1answer
151 views
IIR filter design fitting step response
I have access to the step response of a system and I want to find its poles and zeros without knowing the order of the system.
Consider an example of a step response of the system shown in the ...
1
vote
1answer
115 views
Do you recognize this filter?
I'm trying to decipher the uncommented source code of SoundBox which is a little music tracker written in javascript.
There is an included synthesizer, which applies a filter on the output samples. I'...
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0answers
44 views
IIR (non linear phase) filters
As you know, a nonlinear phase filter (in passband), distorts the frequency contents of passband region of signal. In general, Why do we use such filters in the case they cause distortion in the ...
2
votes
1answer
54 views
Find a stable transfer function $G(z)$ such that $|G(z)| = |H(z)|$
Consider the following causal IIR transfer function:
$$ H(z) = \frac{2z^3 - 4z^2 + 9}{(z-3)(z^2+z+0.5)} $$
Is $H(z)$ a stable function? If it is not stable, find a stable transfer function $G(z)...
0
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1answer
89 views
Applying multiple IIR and FIR filters at once
I would like to appy multiple filters to a signal at once.
Let's assume I got two frequency bands I want to extract. I compute a Butterworth Filter for 300-500Hz and one for 700-800Hz. I would like to ...
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2answers
120 views
How do you program a completely transparent crossover?
Or, if that's too broad, what is/are the most popular algorithms?
Background: I have no formal DSP training but much informal tinkering. I am trying to program a crossover for an audio effect. ...
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1answer
257 views
Z-domain transfer function to difference equation
So I have a transfer function $ H(Z) = \frac{Y(z)}{X(z)} = \frac{1 + z^{-1}}{2(1-z^{-1})}$. I need to write the difference equation of this transfer function so I can implement the filter in terms of ...
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0answers
76 views
Estimating frequency when there's little isolation between signal and noise frequencies
Say I have a signal which is guaranteed to have a frequency between 110-120 Hz but is corrupted by interference signals that're very close to this frequency range. For example, let the interference ...
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0answers
307 views
All pass filter design for group delay compensation
I've designed an IIR bandpass elliptic filter in Scilab with the following parameters.
Sampling Frequency = 25000 Hz
Lower cutoff frequency = 100 Hz
Upper cutoff frequency = 150 Hz
Pass band ripple = ...
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0answers
165 views
IIR filter group delay
I've designed an IIR bandpass elliptic filter in Scilab with the following parameters.
Sampling Frequency = 25000 Hz
Lower cutoff frequency = 100 Hz
Upper cutoff frequency = 150 Hz
Pass band ...
0
votes
1answer
190 views
Stability condition for an iir filter
I have been out of touch with DSP for a while. I was trying to refresh my basics and ended up with this doubt on IIR filter stability condition. I understood that for an iir filter to be stable, the ...
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1answer
29 views
What does “ripple limit cutoff” mean?
So I'm reading the datasheet for MAX98357A.
It's an audio amplifier that receives digital signal using I²S bus and has integrated digital low-pass filters of the IIR and FIR types.
In addition to ...
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3answers
199 views
Distinguishing FIR and IIR from difference equation
Find the transfer function of the difference equation $$y_n = x_n + 1.2y_{n-1}$$
I fail to understand how one can distinguish between an FIR filter and an IIR filter by looking at the equation given ...
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0answers
150 views
Confusion over impulse invariance, matched z-transform, and bilinear transformation methods
In the DSP course that I am taking in my university as an undergraduate student, three methods are presented for mapping analog filters to digital filters - namely, impulse invariance, matched z-...
1
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1answer
122 views
Real-time modulated IIR filter
I've been learning to implement an IIR filter for a synthesizer project. It is now more or less stable when the parameters are constant, but ultimately I want the parameters to be arbitrarily ...
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0answers
59 views
How do I convert a two-pole two-zero transfer function from the s-domain to the z-domain?
I'm trying to convert the following IIR transfer function from the s-domain to the z-domain:
$$
H(s) = \displaystyle\frac{\frac{s^2}{\omega_z^2} + 2\zeta_z\frac s\omega_z + 1}{\frac{s^2}{\omega_p^2} + ...
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votes
2answers
64 views
How many coefficient sections should I select when designing filters with MATLAB FDATOOL?
I attach a picture about the results of a filter design in Matlab.
It says that it has 12 sections. One section contains the coefficients of the transfer function. If I'm implementing this filter in ...
3
votes
1answer
75 views
Can a Goertzel filter response be mapped to a Direct Form II Biquad IIR Filter
I am looking at the structure of the Goertzel Filter, and it seems like I can map its coefficients to the standard implementation of the CMSIS DSP Biquad Cascade IIR Filter. Is this possible or should ...
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1answer
76 views
Is this sampling frequency right?
I designed a Butterworth second order bandstop filter on Matlab with the following parameters:
Notch frequency: 150 Hz (the frequency I want to remove)
Bandwidth = 8 Hz, that is
Fc1=146 Hz
Fc2=154 ...
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0answers
21 views
should block diagrams in Direct Form 1/2 contain empty branches to fit structure?
When creating a block diagram in a well-recognized structure (Direct Forms 1&2 in particular), does one remove branches where the coefficient is 0?
This picture includes a coefficient of $b_1=0....
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2answers
67 views
Can I combine an IIR (an EWMA) with a maximum?
I'd like to have a exponentially weighted moving average (EWMA) which is raised to the value of the input signal whenever this is higher than the filter output. This taking of the maximum shall take ...
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4answers
70 views
Can I use IIR or FIR to get a sliding mean?
My output signal shall be computed by (meta code):
o = 0 # or some arbitrary initial value
for i in input:
o = (o * 99 + i) / 100
print o
I call this a "...
0
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1answer
29 views
historical context of impulse response-convolution
Hi All: I have zero background on the history of LTI systems so I was wondering when the concept of LTI and the fact that an LTI signal can be be completely described by its impulse response came ...
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1answer
183 views
Design Lowpass Filter With -7.5 dB/Octave Rolloff
I am working on a project that needs a lowpass filter with a -7.5 dB/Octave rolloff. This is somewhere between the rolloff of a one-pole and two-pole filter, so I wanted to ask what some standard ...
0
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1answer
259 views
Get difference equation of a filter from MATLAB transfer function coefficients
I need to get the difference equation of a specific elliptic filter.
I calculated the transfer function coefficients in MATLAB with:
...
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votes
2answers
557 views
Matlab `filtfilt` provides excessive transient
I observed that filtfilt suffers from an undesired behavior when I provide IIR bandpass filters having steep transition bands. Specifically, the output signal exhibits excessive transient response; ...
