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25 views

Connection between positive feedback at DC and real-axis right-half-plane pole(s)

(Context provided here, question summarized at the end.) Suppose I have an open-loop transfer function with two coincident left half plane poles like $$ H(j\omega)=\frac{-H_0}{(1+j\omega RC)^2} $$ ...
1 vote
1 answer
83 views

Zero crossing count vs zero crossing rate: does it make any difference?

I am trying to make a feedback howling detection program for an audio DSP chip I made a very crude one by counting zero crossings, doing something like this: ...
3 votes
2 answers
4k 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 ...
0 votes
0 answers
29 views

How to accomodate feedback bits from Base Station to devices in LTE or 5g?

I am trying to think of a way in which the base station (BS) can send say 100 bits of feedback to devices in my cell. My confusion is what is a good way to send this feedback bits. This is during the ...
0 votes
1 answer
214 views

How do I reduce a block diagram with just a line as a feedback loop, I dont get how it adds K to the denominator

How do I reduce a block diagram with just a line as a feedback loop, I dont get how it adds K to the denominator. The bottom equation is supposed to be the answer.
2 votes
1 answer
81 views

What does the frequency of oscillating microphone feedback depend on?

Pointing a microphone to a connected loudspeaker creates a feedback path and usually results in acoustic resonance, which manifests in a sustained oscillation: https://youtu.be/_XTtjZ8aZbc. A similar ...
1 vote
2 answers
74 views

Feedback stabilizes unstable systems?

Can feedback stabilize a unstable system?I guess so since we may get rid of any poles in the positive complex plane by feedback but I am not sure.
0 votes
2 answers
57 views

To create feedback, does the peak to peak amplitude of a signal loop have to have an amplification factor (gain) that reaches zero?

In technical terms, feedback occurs when the gain in the signal loop reaches "unity" (0dB gain). How to Eliminate Feedback Peak-to-peak amplitude (abbreviated p–p) is the change between ...
0 votes
2 answers
243 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 ...
2 votes
0 answers
230 views

Introducing Feedback to Miller Puckette's Time-Domain Pitch Shifting Algorithm without Discontinuities

I've implemented Miller Puckette's time-domain pitch shifting algorithm (http://msp.ucsd.edu/techniques/v0.11/book-html/node125.html) in PureData's help files in C++ (my code here: https://github.com/...
1 vote
1 answer
52 views

Did Dialup Modem use closed or open loop power/volume control? How did they determine Tx level?

I have been reading about dialup modems, but one thing I cannot seem to find out about is how implementers determined optimal transmit power/volume. Is this part of the echo cancelation framework? The ...
1 vote
3 answers
238 views

How can you see from the transfer function of a system that it has feed forward/feedback elements?

Furthermore, how can you see from the pole/zero plot if the system has feed forward/feedback elements?
0 votes
1 answer
795 views

Power Spectral Density of a Filter

I need to calculate the output power spectral density of the following digital filter My calculations are as follows: $y\left(n\right)\:=\:x\left(n-1\right)+d\left[x\left(n-1\right)+x\left(n\right)\...
1 vote
1 answer
41 views

Signal that destabilises a positive feedback path with nonunity feedback

I am just starting to learn about feedback systems. There are a few questions that have me stumped, this being one of them. Could someone please help? Thanks! Question: Find a signal that destabilizes ...
3 votes
2 answers
1k views

Why does the control effort increase if the bandwidth of the system is higher then the bandwidth of the plant?

I am studying control systems and I am focusing on the control effort. I have seen that if I place a pole at higher and higher frequencies, if the bandwidth of the system goes above the bandwidth of ...
5 votes
3 answers
1k views

Frequency warping when integrators are replaced with backward-euler and forward-euler integration

Resonant controllers are used in the power industry. The transfer function is $G_{res}(s) = \frac{K_i s}{s^2 +2\omega_c s+ \omega_o^2}$ The "textbook" discrete implementation is depicted in ...
1 vote
0 answers
84 views

How can I correct the settling time when implementing a pre-filter (reference filtering)?

I have designed a controller for the speed of a motor, I calculated that for a settling time $0.1 \; s$, it works when I test it without pre-filtering. However, I need $0$ overshoot, so I implemented ...
2 votes
1 answer
89 views

Does a RHP zero imposes some limitation in the time domain?

I am studying control systems and I have seen that a non-minimum phase zero imposes a limitation on the bandwidth, which is that the bandwidth has to be lower than the frequency which is half the ...
2 votes
1 answer
234 views

Controller in the feedback path?

What happens if the controller of a closed-loop system is placed in the feedback path before the summation point, instead of between the summation point and the plant to control? Are we allowed to do ...
0 votes
0 answers
30 views

Effect of delayed feedback on sinusoid of frequency corresponding to delay

Question: What is the effect of a delayed feedback path with nonunity gain G on a sinusoid of frequency corresponding to the delay? Plot the effective gain as a function of G. I think this will ...
0 votes
2 answers
195 views

Non-causal FIR filter in the feedback loop

I have a feedback loop with a transfer function $H(z) = \sum_{i=0}^{L-1} h(i) z^{-i}$. Is there a way to make this FIR filter non-causal? If it was a feed-forward filter, we could simply do so by ...
2 votes
2 answers
446 views

How can initial conditions be taken into account to calculate a system's terminal value using the final value theorem or some other technique

I wish to calculate the Final Value of the following system given initial conditions not at rest, and assuming the X will not change from its initial condition value. The transfer function is $$H(z) = ...
3 votes
1 answer
169 views

Discrete time Final Value Theorem applied to feedback system

I wish to calculate the Final Value of systems in which a high pass filter of the output feeds back into the input. A simple example would be: where is a 1st order high pass filter with transfer ...
0 votes
1 answer
175 views

How does the intuitive notion of causality fit in with control systems?

Edit: By causality, in this question, I do not mean the traditional mathematical definition in the theory o signals and systems; I mean causality as in an intuitive 'what's moving/pushing what notion'....
2 votes
1 answer
174 views

How to modify zeros and poles in a delta-sigma modulator loop?

In this specific case, I am modeling a delta-sigma analog-to-digital converter with a basic loop in which the output $V$ is fed back with unity gain to be subtracted from the previously sampled input $...
4 votes
2 answers
78 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 ...
0 votes
2 answers
434 views

Role of Power Metric and LPF in AGC(Automatic Gain Controller)

I am trying to understand & implement simple toy AGC system . Few questions while reading about it, 1) How POWER metric came into picture, why not other metric like absolute value to control ...
0 votes
2 answers
1k 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, $Af$ ...
1 vote
2 answers
2k views

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 ...
9 votes
4 answers
16k 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 ...
1 vote
0 answers
30 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[0]=(...
1 vote
0 answers
37 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 ...
6 votes
1 answer
321 views

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 ...
0 votes
1 answer
448 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 ...
0 votes
1 answer
1k 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 ...
2 votes
0 answers
460 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) ...
0 votes
1 answer
96 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 ...
1 vote
1 answer
481 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 ...
0 votes
2 answers
2k 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? ...
0 votes
0 answers
59 views

Finding lossless coefficients to multi-tap feedback delayline

I have a digital delayline code which looks like this: ...
3 votes
1 answer
926 views

How can a system be unstable if $L(j\omega)$ is never exactly $-1$?

Say we have a linear system with unity feedback, with loop transfer function $L(j\omega)$. The closed-loop transfer function from reference to output is $T(j\omega) = \frac{Y(j\omega)}{R(\omega)}=\...
3 votes
1 answer
955 views

What is the total impulse response in a system with feedback interconnection?

Let's assume that we have a system with a typical feedback interconnection where the output is given by the following equation: $$y(t) = \left(x(t) - z(t)\right) \star h_{1}(t) \tag{1} $$ where: $$z(...
2 votes
1 answer
228 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 ...
5 votes
1 answer
1k 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 ...
0 votes
0 answers
232 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 ...
1 vote
1 answer
242 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 ...
1 vote
1 answer
2k 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 ...
3 votes
2 answers
215 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 ...
4 votes
1 answer
3k views

Acoustic feedback detection algorithm

I am woking on an sound processing application where I have limited processing resources. I need to be able to detect acoustic feedback and then signal that such an event occurred. I am not concerned ...
12 votes
1 answer
4k views

What is the "waterbed effect" in control system design?

I recently stumbled across some notes on the "Waterbed effect" in some notes by A. Megretski for an MIT course on "multivariate control systems". Here's an excerpt: A common effect, usually ...