# Questions tagged [allpass]

Use this tag for questions related to filters that change the phase relationship of a signal, but does not change the gain (amplitude) of the signals.

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### Phase correction using second order all pass filters/LMS with Wiener-Hopf equations

I am working on phase correction algorithms. Can anyone help me understand how can the following diagram be used for phase correction: Additionally, for a channel function suggested How determine the ...
40 views

### Plotting Frequency Response Magnitude and Phase for first order all pass filter

Having trouble plotting the frequency response characteristics for first order all pass filter. The Magnitude is expected to be constant across entire freq and Phase is expected to be only decreasing (...
65 views

### Is there a simpler way to calculate the amplitude response of the following filter

I would like to calculate the amplitude response $|H(z)|$, $z=e^{j\omega}$, of the following filter: $$H(z)=\frac{\frac{b}{2}+z^{-2}}{2+bz^{-2}}$$ and I would like to avoid using Euler's formula and ...
98 views

### Getting a single feedback peak from a basic 4 stages phaser

I try to set a very basic 4 stages phaser (two 2-pole all-pass filters), with a particular feedback path where only one peak is raised at center frequency when the feedback is above 0. The following ...
81 views

### How do you calculate the group delay in samples of a Biquad Filter at a given frequency from the coefficients?

If I have a BiQuad all-pass filter with a given set of coefficients such as: g: 0.903228 a1: -1.88142 a2: 0.903228 B1: -2.08299 B2: 1.10714 And my operation per ...
299 views

### Presenting an all-pass filter of a high order as a cascade of all-pass filters of the 1-st order

Are all-pass filter of the n-th order just a cascade of N all-pass filters of the 1-st order? There are some nice statements regarding zeros, poles, and gain for the 1-st order. Can those statements ...
76 views

### How to calculate an All-Pass filter quantization coefficients

Given $$H(z) = \frac{z^{-1}-0.8}{1-0.8z^{-1}}\text,$$ does the filter stay an All-Pass filter after quantization of coefficients? If so, how can I prove it mathematically?
601 views

### How to calculate the delay generated by a 2nd order all-pass filter

I'm trying to simulate the dispersion effect of a stiff string in a digital waveguide system, by using second-order all-pass filters. I use a second order all-pass filter with this transfer function:...
908 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 = ...
107 views

### Calculating Stability of Phaser Feedback Loop

I have been doing some experiments with phaser programs. I really like setting the phaser feedback to really high levels, such that the effect is really metallic and resonant, almost like a physical ...
126 views

### Why these cross-connections in the allpass filter?

Why these cross-connections in the allpass filter? and what do negative and positive $k_1$ really refer to? Is it when the signal is going downwards or is it when the signal is below the zero line?
623 views

### Allpass Filters - Causal and Stable

So I have been learning about how to test systems for causality and stability but I am confused about the implications on their unit circle representation. Would it be safe to say that a causal and ...
355 views

### Given a causal LTI system with a transfer function, determine if the system is an all-pass filter

We are given a transfer function of a causal LTI system and must determine if it is an all-pass filter: $$H(z) = \frac{1 + 4z^{-2}}{4 - z^{-2}}$$ To the best of my recollection to determine if a ...
1k views

### IIR Hilbert Transformer

I'm beginning to explore discrete Hilbert transformers - ways to achieve 90°. phase shift across a band of perhaps 6 kHz at a 44.1 kHz sampling rate. I'm trying to stick with IIR filters in order to ...
330 views

### A property of all-pass filters

Let $G(z)$ be a real coefficient stable all-pass transfer-function with degree greater than zero. Then it can be shown that $|G(z)| < 1$ for $|z| > 1$: Given that the poles occur in complex ...
157 views

### how to design LPH and HPF from APF

I came across a concept that says we can design LPH and HPF from APF when the transfer function of the two APFs given as \begin{align}A_0(z)&=1\\ A_1(z)&=\frac{-a+z^{-1}}{1-az^{-1}}\\\\ H_{...
1k views

### Finding minimum-phase/allpass of transfer function

I am trying to find the minimum-phase system of the transfer function $H(z) = \frac{2 + 3.125z^{-2}}{1-0.9z^{-1}+0.81z^{-2}}$. I know I need to find and remove the allpass (basically reflect the two ...
706 views

### filtering in frequency domain

I am performing decorrelation of two channels of audio using all pass filtering. The two all pass filters for two channels are of very high order (>1000 but with not all coefficients non zero). I have ...
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### How to design an all pass type filter with inverted phase response?

I want to model a "negative dispersion" in waveguides. Is it possible to design an all pass filter with inverted phase response? (e.g. -pi at 0 and pi at Nyquist)? I feel :) this could be possible ...