What is Signals and systems: Definition and 57 Discussions

In signal processing, a signal is a function that conveys information about a phenomenon. In electronics and telecommunications, it refers to any time varying voltage, current, or electromagnetic wave that carries information. A signal may also be defined as an observable change in a quality such as quantity.Any quality, such as physical quantity that exhibits variation in space or time can be used as a signal to share messages between observers. According to the IEEE Transactions on Signal Processing, a signal can be audio, video, speech, image, sonar, and radar-related and so on. In another effort to define signal, anything that is only a function of space, such as an image, is excluded from the category of signals. Also, it is stated that a signal may or may not contain any information.
In nature, signals can be actions done by an organism to alert other organisms, ranging from the release of plant chemicals to warn nearby plants of a predator, to sounds or motions made by animals to alert other animals of food. Signaling occurs in all organisms even at cellular levels, with cell signaling. Signaling theory, in evolutionary biology, proposes that a substantial driver for evolution is the ability for animals to communicate with each other by developing ways of signaling. In human engineering, signals are typically provided by a sensor, and often the original form of a signal is converted to another form of energy using a transducer. For example, a microphone converts an acoustic signal to a voltage waveform, and a speaker does the reverse.Information theory serves as the formal study of signals and their content, and the information of a signal is often accompanied by noise. The term "noise" refers to unwanted signal modifications but is often extended to include unwanted signals conflicting with desired signals (crosstalk). The reduction of noise is covered in part under the heading of signal integrity. The separation of desired signals from background noise is the field of signal recovery, one branch of which is estimation theory, a probabilistic approach to suppressing random disturbances.
Engineering disciplines such as electrical engineering have led the way in the design, study, and implementation of systems involving transmission, storage, and manipulation of information. In the latter half of the 20th century, electrical engineering itself separated into several disciplines, specializing in the design and analysis of systems that manipulate physical signals; electronic engineering and computer engineering as examples; while design engineering developed to deal with the functional design of user–machine interfaces.

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  1. Daniel Petka

    Why does a series of pulses generate a pitch?

    Here's the thing: the ear detects a pitch by splitting a sound wave into it's frequency components in the cochlea, which is in a way a spatial Fourier transform (ish...) But I never liked this analogy because it doesn't explain why I hear a pitch when a series of pulses entern my ear. A single...
  2. Yalanhar

    Convolution of 2 Signals: Finding the Sum and Limits of y[n]

    ##x[n] = (\frac{1}{2})^{-2} u[n-4]## ##h[n] = 4^{n} u[2-n]## So I plotted x[k] and h[n-k] in picture but x[n] is 0 for n < 4, therefore ##y[n]## only has value for n >= 4. Therefore my sum is like that: ##y[n]=\sum_{k=4}^{\infty} 4^{n-k} (-\frac{1}{2})^k## ##y[n]=-4^{n}...
  3. A

    Trying to intuit the unit impulse response

    Homework Statement Hi there, I've been trying to gain some intuition on how the convolution sum works, but as I dig deeper I am realizing that there is an issue with my intuition of signals and systems, in particular the unit impulse response. My issue is trying to understand how a unit...
  4. G

    Engineering Analysis of a servo motor

    Homework Statement 2. Homework Equations [/B] I'm studying a mathematical behaviour of a servo motor and I need some help to understand it. The output signal is \$\beta (t)\$, representing the angle rotated by the axis at instant t, in relation to the equilibrium position. On the servomotor...
  5. L

    Understanding the discrete time Fourier transformation

    Let's consider a signal which is continuous in both time and amplitude. Now we consider the amplitude of this signal at specific time instants only. This is my understanding of sampling a signal in time domain. When performing a Fourier transform on a time discrete signal, we have to apply the...
  6. C

    How Do You Analyze a Continuous Time LTI System Using Differential Equations?

    Homework Statement continuous time LTI system is given with differential equation y'(t) + 5y(t) = 10u(t) a) Find transfer function of system and determine is it stable or not. b)Find frequency characteristics (amplitude and phase angle) of given system c) Find impulse response using Laplace...
  7. S

    Power/Energy Signal Homework: u[n] - u[n-4]

    Homework Statement Determine whether u[n] - u[n-4] is a power or energy signal. Homework Equations The Attempt at a Solution I am stuck here. I don't know how to simply further. Please help.
  8. O

    Signals and Systems Theory Question

    Homework Statement [/B] How are we able to go from the first line to the second line and then the second line to the third? Homework Equations Euler Identity: e^j(theta) = cos(theta) +jsin(theta) The Attempt at a Solution This problem is more about preliminary theory in my opinion so I tried...
  9. R

    Base excitation of undamped Spring-mass system

    Homework Statement I am a little stuck/unsure in an homework question for my signals and systems course. See question sheet attached. I have been able to do question 1 for the first section using FBD, and I have solved the DE using Laplace Transforms (See below for my solution). I am both...
  10. S

    Is the Integrator Linear in t?

    Homework Statement Determine whether the system is linear Homework Equations Superposition The Attempt at a Solution I am comfortable solving the case where the bounds are from negative infinity to t. I have provided an example of that solution I found online. I attempt to solve that...
  11. Manoj Sahu

    How to calculate the energy and power of a signal?

    I would like to improve my knowledge of signals. I just came across this topic while reading a book. So I would like to know how to find out that the given signal is power signal or energy signal. For example please solve the following and give your explanation in reference to that. e^j(2t+π/4)
  12. Woa90210

    What was most helpful understanding Signals and Systems?

    Hey guys! This is my first day on the forum so, hey! I'm a third year electrical engineering student and I'm really having some trouble with Signals and Systems so I want to know what helped other people understand it so that maybe I could try some of their methods. What were your biggest...
  13. Captain1024

    Finding Impulse And Frequency Responses

    Homework Statement Consider a LTI system defined by the following difference equation: ##\mathrm{y}[n]=-2x[n]+4x[n-1]-2x[n-2]## a) Determine the impulse response of the system b) Determine the frequency response of the system Homework Equations DTFT...
  14. G

    Signals and Systems + Electromagnetics classes

    Hi All, I am a EE student and thinking about doing the following classes in Spring 16 - Signals & Systems + Electromagnetic + Physics 3. Any suggestions is Emag and Signal and systems very hard?, what Math do you need? (Dif Eq) Is it a bad a idea taking these classes at the same time...
  15. MathematicalPhysicist

    Are There Engineering Applications for the Generalized Z-Transform?

    Has there been any applications in engineering to the following generelization to Z-transform? ##X(z) = \sum_{n=-\infty}^\infty x[n] e^{-zn}## We get the ##z##-trasnform by using the substitution ##z \mapsto Log(z)##. Thanks in advance.
  16. D

    Sketch and mathematically represent pdf of given signal

    Homework Statement I've been asked to sketch and mathematically represent the pdf of 2 signals: (a) rep2T{5 rect(t/T) - rect((t-T)/T)} (b) rep2T{2 rect(t/T) + 4Arect(2t/T)} A(t) is the lambda function A(t) = 1- t for 0 <= t <= 1 1+t for -1 <= t <= 0 Any help would be much...
  17. H

    Signals and Systems | Impulse Response Problem

    Homework Statement Find the impulse response for the systems governed by the following equations: 3y(t)'+5y(t)=x(t)+x(t)'[/B]Homework EquationsThe Attempt at a Solution I tried to obtain the homogeneous solution for h(t)[/B] and then I failed to obtain the coefficients of the solution
  18. M

    Discrete Fourier Transforms of Signals

    Homework Statement Homework EquationsThe Attempt at a Solution I'd like to see if I have the right line of thinking in my solutions: a. The sampling frequency should be such that no aliasing or folding occurs, so it should be twice the frequency of the original signal. $$x(t) = -17...
  19. E

    Is having Circuits 2 a corequisite for Signals and Systems viable?

    Hello all, I am currently studying as an EE and realized I messed up something with my career path. I am not sure if it possible to get an internship at a company for primarily DSP if you haven't taken a DSP class? If not, things could be mended if it were possible to take circuits 2...
  20. S

    [Signals and Systems] What's the signinfance of negative time?

    Hello all, This one thought came to my mind just now. What's the physical significance of signal representation in negative time, i mean second and third quadrant. So for example, sin(t) and sin(t).u(t) aren't they same for all practical purposes? I know, mathematically they are...
  21. mathwhiz

    Preparing for Signals and Systems

    Signals and Systems Vs Circuits I I really just would like to know which course, in your opinion, was more difficult circuits I or signals? I've already taken circuits and signals is up next. Also, what should I be reviewing in order to prepare myself, during the break, for Signals and...
  22. R

    EE Course: Signals and Systems

    Hi all, I'm in a bit of a dilemma. I have an opportunity to take Signals and Systems over the summer. However, I have not taken Differential Equations yet. A course on Electric Circuits is a prerequisite for this class and I ended up taking that last semester without any DE knowledge LOL...
  23. A

    Best Signals and Systems book?

    What is the best book out there for Engineering Signals and Systems? One that is clear & easy to understand and has many different problems with solutions. The book I am using has no solutions and there is no way to check my work. I hope someone knows a similar book...
  24. S

    Is Signals & Systems Memoryless/Linear?

    1) y(t)=dx(t)/dt Is this system memoryless? 2) y(t) = 0 if x(t)<0 x(t) + x(t-2) if x(t)>=0 Is this system linear? Thankyou :)
  25. W

    Mathematical treatment of signals and systems

    Hi there, I am looking for books that treat signals and systems from a mathematical perspective. When I say "signals and systems", I am referring to the typical second/third year material taught in EE programs: system characteristics (causality, memory, stability), LTI systems, linearization...
  26. R

    Signals and Systems - Power and Energy level signals calculation

    Homework Statement http://i.imgur.com/j8JdV.png Homework Equations http://i.imgur.com/Wobmo.png The Attempt at a Solution I wasn't really sure where to start with. Can energy level be calculated at any of these, since the signal stretches to infinity? I'm very thankful for any...
  27. L

    What are the Best Books for Studying Signals and Systems?

    Hi all, I will be studying Signals and Systems later this year and it would be great if you could recommend me some books, tell me why you prefer them over others and describe them a little. The contents of the course will be both time-continous and time-discrete signals, sampling, Z, Fourier...
  28. M

    Homework Help Signals and Systems

    I was trying to solve out this problem for homework and I came to the answer of all of them being false because they all went to infinity...but I have a gut feeling that this is wrong.
  29. G

    Signals & Systems: Determine System Output

    Homework Statement Given: Impulse response: h(t) = u(t-1) - u(t + 1) (where u(t) is the unit step function) System input: x(t) = t*u(t) - t*u(t-2) Determine System output: y(10) = ? y(1) = ? max y(t) = ? |y(t)| is max at t = ? Homework Equations Convolution integral? y(t) = -∞∫∞...
  30. R

    Signals and Systems (System Properties)

    Homework Statement Indicate following properties for the system with the given input-output equation: -Linearity, Causality, Time Invariance, memoryless or not and explain why? Homework Equations y(t) = ∫t-∞ (t - λ) x(λ) dλ The Attempt at a Solution lets say X(t) is the...
  31. S

    Difficulty - Signals and Systems

    Hi In my notes I came across the following sentences:- Any signal consisting of the system's characteristic mode is sustained by the system on its own. The system offers no obstacle to this signal. Not getting what it means. Please, a little help needed. :-) Thanks salil
  32. B

    Signals and Systems: Deriving length of discrete convolution signal

    Homework Statement If a signal f1[n] begins in a moment N1 and ends in moment N2, and signal f2[n] begins in the moment M1, and ends in the moment M2, derive the formula which states in which moment begins and ends the signal f1[n]*f2[n] Homework Equations The Attempt at a Solution I...
  33. B

    Signals and Systems, basic graphs

    So I am 2nd year now and we started this new course Theory of Signals. Already I bumped into a wall when it came to understand basic stuff. Here is what I mean [PLAIN]http://pokit.org/get/0864633c869b647116b980428a07d4f1.jpg Here we have 4 functions, each representing one type of...
  34. N

    Help with Signals and Systems Differential Equation Problem

    Hey guys, I was wondering if I could receive any help on a homework problem I have. I need to find the differential equation relating the input to the output. I've began working on it but feel like I've hit a brick wall in my work, any input? Homework Statement Attachment - Problem...
  35. J

    Input output relations in signals and systems

    Homework Statement I have a trouble understanding what would be the output when for example we say let's input the signal x(k*n) or x(n-n0) to the system... this has given me problems when having to solve systems for which I have to check the property of time invariance suppose we have a...
  36. T

    System properties e.g. causality/memory (Signals and Systems)

    Homework Statement Determine if the system y(t) = sin(x(t)) is time invariant, linear, causal, and/or memoryless. Homework Equations None. The Attempt at a Solution The system is time invariant and is non-linear, but I don't understand why it is causal and has memory.
  37. D

    Signals and Systems: Determine if the signal is periodic or nonperiodic

    Homework Statement Determine whether or not each of the following signals is periodic if signal is periodic determine the fundamental period (note that these are discrete not continuous signals) Show your solutions 1. x(n) = \cos^3(\frac{\pi(n)}{8}) 2. x(n) =...
  38. M

    Inverse Laplace transform Signals and systems

    Homework Statement Compute Y(t). Homework Equations Y(s)= (s(2s+11)+ω(8s+4ω^2))/((s^2+ω^2)(s+9)(s+2)) The Attempt at a Solution (s(2s+11)+ω(8s+4ω^2 ))/((s^2+ω^2)(s+9)(s+2))= A/(s^2+ω^2 )+B/(s+9)+C/(s+2) Every example I have looked at does not have the ω variable, but I...
  39. E

    I think I'm going to fail Signals and Systems?

    Hi friends, I'm new in this forum and very happy to be here. I need your guidance on what to do with my Signals and Systems course which I expect to turn into a failure. I'm studying Electronics Engineering and I think I'm going to fail Signals and Systems because I got 9 out of 100 on my first...
  40. D

    Signals and Systems [Calc the Fundamental Period]

    Homework Statement Determine the Fundamental Period and Frequency I got this question wrong on My midterm and I was wondering if you guys could give me some feedback on it x(t) = cos[50(pi)t] + sin[15(pi)t] Homework Equations T(fundamental Period) = 2(pi)/w // w is the frequency...
  41. C

    In search of a great book for introductory signals and systems

    Hi all, I am enrolled in an introductory signals and systems course at my university. I don't like talking down on my professors but in this case I can't help it. He is one of the worst teachers I have had in my life. I have visited his office hours but he's not really helpful in there...
  42. A

    Convolution - Signals and Systems

    I will make this my discussion thread. I have many questions to ask which I will post here. Please keep checking. All help will be appreciated. My first question is: For discrete signal, we use variable 'n' and for continuous signal, we use variable 't'. But is the convolution integral valid...
  43. K

    Signals and Systems: Deriving differential equation from block diagram

    Homework Statement Consider the block diagram below. Find the differential equation of the system. Homework Equations None, other than understanding how block diagrams work. The Attempt at a Solution My attempt is posted below, as an image. The reason I am having such trouble is...
  44. F

    Signals and Systems, system properties

    I know that y(t) = t x(t) is unstable, for bounded inputs yielding unbounded outputs, but would y(t) = x(t)/ t also be unstable? when t is going in the negative direction? please help. test Monday.
  45. L

    Signals and Systems - Convolution

    Homework Statement http://img166.imageshack.us/img166/1162/untitledte2.jpg Homework Equations Convolution y[n] = x[n] * h[n] The Attempt at a Solution I've never done convolutions going backwards.. right off the bat, I know I'll noly have 2 terms in the convolution sum...
  46. D

    Signals and Systems example problems?

    Are there any resources on the web that provide example problems (with solutions) to Signals problems? My textbook (shown below) lacks any clear example problems (shows answers without showing you how to get them). If someone could point me toward examples of Convolution, Fourier series, or...
  47. M

    Signals and Systems: Response of LTI systems to Complex Exponentials

    How will we evaluate the integral for calculation of Amplitude Factor for an LTI system for which the input and output are related by a time shift of 3, i.e., y(t) = x(t - 3) The answer is: H(s) = e^(-3s) I want to understand the Mathematics behind the evaluation of the integral...
  48. H

    An introduction to signals and systems

    Hi everybody, I'm a freshman and i want to study signals and systems. so I'm seeking for a good introductory book. I've heard about the book "Signals and Systems" written by Oppenheim and Wilsky. So is Oppenheim's book suitable for a beginner? If you know a better introductory book...
  49. maverick280857

    Simple question [Signals and Systems]

    Hi The following question is from Oppenheim/Wilsky/Nawab chapter 1. Consider a periodic signal x(t) = 1 for 0 \leq t \leq 1 x(t) = -2 for 1 < t <2 with period T = 2. The derivative of this signal is related to the impulse train g(t) = \sum_{k = -\infty}^{\infty}\delte(t-2k) with period T...