# Questions tagged [feedback]

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### Determine stability of feedback system from open loop transfer function and Nyquist stability criterion gives different results

I'm confused due to the fact that the Nyquist stability criterion and looking at the transfer function doesn't give the same results whether a feedback system is stable or not. When I have the system ...
95 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 ...
23 views

### Quantifying the frequency shift of a delay with LP filtered feedback

I am working at a Karplus-Strong sound synthesis technique where an excitation impulse is subjected to a delay with feedback and a one pole LP filter in the feedback line. The process is simply y=(...
28 views

### How can we do exact simulation for digital systems? [closed]

In digital control system, there are two basic techniques for finding the best digital controller. First, called the discrete equivalent, we find the continuous compensation and then discretize (best ...
44 views

### Is there any solution for this bandpass feedback overload problem (besides increasing sample rate)?

I have been working on a physical modeling string (eg. guitar/piano) synthesizer which is nearing completion. It is based on a modal array of resonant bandpasses, where each bandpass is set by Q and ...
77 views

### Why is my filter unstable and self-oscillating in this case?

I am using resonant bandpasses to simulate modes of guitar/piano strings for audio synthesis. While attempting to introduce coupling effects I have encountered a problem. I will illustrate with some ...
28 views

### Decorrelation for Adaptive Feedback Cancellation: How does it work?

I am going through lecture slides on adaptive feedback cancellation right now, and several decorrelation measures are mentioned. As I understand, these are important in order to avoid a bias in filter ...
78 views

### Calculate transfer function of two parallel transfer functions in a feedback loop

I have rational transfer functions: $$H_1(z) = \frac{ b_0 + b_1z^{-1} + b_2z^{-2} }{a_0 + a_1z^{-1} + a_2z^{-2}}$$ $$H_2(z) = \frac{ q_0 + q_1z^{-1} + q_2z^{-2} }{p_0 + p_1z^{-1} + p_2z^{-2}}$$ And ...
226 views

### Feedback Filtered-x LMS algorithm: question about theory

I was reading some of papers about the Active Noise Cancellation; in particular about the Filtered-x LMS algorithm, also known as FxLMS. It seems that classic FxLMS (also called Feedforward FxLMS) ...
53 views

### Calculating an in-loop signal as part of a hierarchical control loop

I've got a control system with two feedback paths, with each path going to a different actuator that corrects the error in the system. One feedback path provides feedback at low frequencies, and the ...
132 views

### DSP using audio IO from PC using C++

This is my first question on dsp. I am looking for something very simple here and I am sure there are libraries that will do pitch recognition and FFT but my requirement is very simple. I have a PC ...
604 views

### What does G(1) = 1 say about a system?

This is a line from a paper I've been reading: The static gain of the closed loop system must be $1$ ($G(1) = 1$) [...] First of all: I know what gain is, but isn't gain dependent upon frequency? ...
52 views

### Finding lossless coefficients to multi-tap feedback delayline

I have a digital delayline code which looks like this: ...
274 views

### Feedback systems & oscillations

The transfer function of feedback system is: $$\frac{V_{\rm out}}{V_{\rm in}} = \frac{A}{1+Af}$$ Where $A$ is the open loop gain, and $f$ is the feedback gain. Now for oscillation to happen, $Af$ ...
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### Is there a strategy for discrete control of a system with dynamics near sample rate?

I'm trying to control a system where the controller sample rate is physically fixed and the plant has significant dynamics on the same order as the sample rate. I understand that one would prefer to ...
7k views

### Do we use closed loop or open loop information in Bode plot, Nyquist plot and Root Locus?

When analyzing a control system via Bode, Nyquist and Root-Locus, are we using open or closed loop information? I'm not able to understand when the poles of the open loop are used and when the one of ...
1k views

### What is the Reference in Control Theory?

I've started studying Control and I've come across some concepts that I'm finding a bit difficult to understand. For example, in the system showed here, there is a signal called "reference" as well ...
177 views

### Is there an existing feedback elimination algorithm that can be implemented in iOS?

The project I'm working on allows a user to speak through a PA system with their iphone as the microphone. Unfortunately, the existing audio units in iOS don't eliminate the feedback between the PA ...
168 views

### Frequency range of acoustic feedback

What is the frequency range in which acoustic feedback can be found? Most importantly, is there some lowest frequency below which one can expect not to find any feedback? My conclusion from the ...
180 views

### Resample with unknown rate change

I am doing digital signal processing for a software defined radio. I have a signal coming in packets of data (several samples) at an average sample rate of approximately some known value FSin. I am ...
711 views

### Allpass filter feedforward/feedback design and code

I want to design/implement a simple feedforward/feedback all-pass filter, and I am having some troubles and questions with it. From Shroeder design (based on J. Smith article here): I came up ...
177 views

### Digital implementation of type I compensation network

I'm looking for advice or references on how to implement a "type I" compensation network of digitally. An analog example is shown in the following diagram: I am familiar with the basics of digital ...
802 views

### Phase Locked Loop Basics

I am trying to better understand discrete-time PLLs. I drew a picture of a simple feedback system here: I want to be able to describe and understand the system at v(t) and y(t). I found a fairly good ...