Questions tagged [time-domain]

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5
votes
6answers
736 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 ...
5
votes
4answers
929 views

Can every type of linear filter be modelled by a convolution?

I have an input time series going through a filter that creates another time series as output. If I assume in first approximation that my filter is linear, does it necessarily mean that I can model ...
4
votes
2answers
10k views

Difference between RMS and a moving RMS

I don't quite get the difference between RMS and a moving RMS. When one calculates RMS, one integrates (or sums in case of a discrete signal) over a period of time(number of samples). When it comes ...
4
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3answers
777 views

Time domain maximum from frequency domain data?

Is it possible to calculate the maximum value of a time-domain signal from frequency-domain representation without performing an inverse transform?
4
votes
1answer
365 views

What is wrong with my residue partial expansion method? (Transfer Function into State-Space Modal/Diagonal Form)

I'm using reference from here and here. This is Laplace transfer function of DC Control Speed System: $$\frac{\omega(s)}{V(s)}=\frac{K}{(Js+b)(Ls+R)+K^2}$$ Where, $\omega$ is the motor angular ...
4
votes
2answers
2k views

Extracting Peak Frequencies Using FFT vs. Time Domain Peak Finding

I am trying to compare two processing algorithms that I believe should be producing very similar results. I am processing acceleration signals over the course of the day and we expect to see a ...
3
votes
1answer
572 views

Confused on the difference between the frequency spectrum of an entire song, and the frequency spectrum of a point in time

I am very much a beginner in this field - but find it really interesting. However I am a little confused on a certain area of knowledge. If I have understood correctly: At any point in an audiosignal,...
3
votes
4answers
2k views

Time synchronous averaging - MATLAB

I have a time domain signal that corresponds to a vibration signal of a machine. I have a second signal that corresponds to a tachometer signal (There is a pulse every one revolution of the shaft). I'...
3
votes
2answers
584 views

Ripple in time-domain using lanczos resampling

I'm seeing ripple in the time domain when resampling a "unity signal", that is, all ones, with lanczos filters. The ripple/error exactly resembles a cosine with a period of the sampling rate - ie. the ...
3
votes
1answer
109 views

Pixel Wise Write into a Video File in MATLAB

A video file (in .ptw format) is read in MATLAB in the form of a 3 dimensional matrix (a structured format). My aim is to process the video in time domain on each coordinate pixel individually and ...
2
votes
2answers
2k views

Finite and Infinite support in time and frequency domain

It's known that signals with a finite support in time has an infinite support in frequency (talking about Fourier Transforms). A common example that is given for the claim is the triangle function ...
2
votes
1answer
62 views

Why aren't the integrator and the differentiator inverse systems?

I have a statement that leads to a paradox, but I'm incapable of finding the part where I'm wrong. The integrator system $$x(t) \mapsto y(t)=\int_{-\infty}^{t}{x(\tau) \, {\rm d} \tau}$$ is a linear ...
2
votes
2answers
944 views

Linear Constant Coefficient Differential Equations: Zero-Input and Zero-State responses

The solution to a linear constant coefficient differential equation of the form $$\sum_{k = 0}^{N} a_k y^{(k)} (t) = \sum_{k = 0}^{M} b_k x^{(k)} (t)$$ can be written as $y(t) = y_{ZI} (t) + y_{ZS} (t)...
2
votes
2answers
2k views

Is it possible to apply a frequency filter a time domain signal?

Is it possible to frequency filter a time domain signal, without converting the signal to a frequency domain.. My question comes in regards how MFCC according to wiki and other pages describe the ...
2
votes
2answers
86 views

Sampling Theorem: T-Sampled Signal

I am stuck in a small question which I am trying to solve. The signal $f$ defined by $f(t) := \text{sinc}(t)$ is to be sampled. How should I draw the illustrations of the $T$-sampled signal $f_{T} = (...
2
votes
1answer
426 views

Time-Frequency Analysis of Big Data - Data Size Reduction: averaging the most appropriate method?

Explanation: I would like to analyse the data from an experiment, which investigates the performance of a mechanical component using sensors, that has generated 2000 CSV files. Each file contains 513 ...
2
votes
1answer
60 views

Why does Phase-locking value show spurious effects at the beginning & end of a signal?

I am trying to understand the behaviour of the phase-locking-value, as e.g. defined here, by some simple examples. Basically, I am creating two signals with the same frequency & amplitude, where ...
2
votes
1answer
452 views

Eigenfunction property for LTI sinusoidal and the sinusoidal steady-state response

All LTI systems possess the eigenfunction property for complex exponential inputs. That is (restricting our attention to periodic complex exponentials), if $e^{j\omega_k t}$ is an input to the LTI ...
2
votes
1answer
1k views

Time scaling of discrete-time sequences and the DTFT

In the second edition of Signals and Systems by Alan Oppenheim, he discusses the DTFT of a "time-expanded" sequence that is effectively a slowed down version of the original sequence and can be ...
2
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0answers
42 views

Determining the right order of time-domain low pass filter for desired cutoff frequency

I've been stuck on a problem regarding complex demodulation of a signal for a while and wondered if anyone could help. Suppose I have a signal $X(t)$ such that \begin{align} X(t) &= A(t)\cos(\...
2
votes
1answer
227 views

How do audiobook players manage to quickly speedup/slowdown playback speed without using more memory?

Many audiobook player apps on Android have a reading speed slider which lets us choose the reading speed e.g. 0.5x 0.75x 1.00x 1.25x 1.50x. This is time-stretching ...
2
votes
1answer
332 views

Is it right to talk about dynamic range on frequency domain?

I'm comparing three frequency response's plots from simulations and experiments and I observed that two of them look like clamped to a DC component, where the max dB value is i.e. 100 and the min is ...
2
votes
0answers
180 views

$\tt ifft()$ function - absolute vs real form

I have multiple files from an experiment in frequency-domain that I would like to use ifft() function to convert to the time domain in R to apply signal processing ...
1
vote
4answers
4k views

Effect of low pass filter on the time domain

Consider an ideal (rectangular profile in frequency domain) low-pass filter (LPF) which simply sets to zero all the frequencies beyond a certain cut-off frequency. Let $x$ be a discrete-time signal of ...
1
vote
2answers
190 views

Where to start with DSP?

I have a DSP exam coming up this summer and I got an abysmal mark on an assignment earlier this year. Obviously, the lecture slides are not enough for me to understand DSP, so I am wondering where can ...
1
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4answers
2k views

Butterworth filter transfer function in time domain

Preliminaries I need to know the response of Butterworth filter in time domain of the following input (at least numerically): $$ x(t) = \theta(t)(1-\exp\{-at\})\exp\{-bt\}, \quad a,b>0,\quad a\gg b ...
1
vote
2answers
130 views

Can a 1-dimensional signal be in a domain other than the time or frequency domain?

In signal processing I have only heard of signals being in the "Time" domain or in the "Frequency" domain, but are there situations where a signal is not in either of these? If so, what are these ...
1
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2answers
631 views

negative value of signals

can we say there is no sound produced when the amplitude is 0? if yes what can we say when the amplitude is negative?
1
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1answer
52 views

Index of stationarity of a time domain signal

During my internship, I've come across a software that calculates a percentage called "Index of stationarity". This index shows how much stationary is the signal. Does anyone have any idea on how to ...
1
vote
1answer
229 views

Why is modern control theory in the time domain instead of the S-domain?

I am not sure if I am missing something, but from what I read I understand that modern control systems work in the time domain rather than the frequency frequency or S-domain. Wikipedia article ...
1
vote
2answers
359 views

Why the following discrete type system,variable accumulator, is time invariant?

$y[n]=T{x[n]}=\displaystyle\sum_{k=n-n_{0}}^{n+n_{0}} x[k]$ it is some sort of moving summer which computes $n^{\text{th}}$ output sample by adding all samples lying within length $n_{0}$ around some ...
1
vote
1answer
61 views

Are there any recursive online max/min filters for time-series

Are there any online recursive filters that can approximate local, time-varying minimum and maximum values of a time series?
1
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1answer
192 views

How to determine the phase of a time-sampled periodic signal?

I know this is a rather common and a rather simple problem, but somehow I can't find a solution that is equally simple to understand (and implement). I have a signal that closely resembles a noisy ...
1
vote
2answers
780 views

Convolution and Modulation Theorem with Octave Example

As far as I know, convolution theorem stated that $$ x[n] * y[n] = X(e^{j \omega}) Y(e^{j \omega}) $$ $$ X(e^{j \omega}) * Y(e^{j \omega}) = x[n] y[n] $$ I tried a simple experiment using GNU Octave ...
1
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2answers
259 views

Is there an equivalent time-domain operation to the spectrum averaging in Welch's method?

In Welch's method a time-series is segmented and then the subsequent FFTs of the segments are averaged. Is there an equivalent time-domain operation? I guess doing the the Welch estimate and ...
1
vote
1answer
66 views

Frequency of Signal of a point tracked in a video?

I have used MATLAB to track a feature point (corner point) using Lucas-Kanade tracker and plotted its movement through each frame now I need to find its frequency content, how should I find it? (I ...
1
vote
2answers
2k views

Determine Phase Difference and Time Delay Between Two Pulsed Sinusoidal Signals

I am working on a code that generates two signals: A pulsed sinusoidal signal ($1\textrm{ MHz}$) beginning at $0$ phase, and lasts for say $5\ \mu\text{s}$, then trails zeros. The other signal has the ...
1
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1answer
42 views

Train of impulses in frequency domain

Why compressing a train of impulses in time domain produce a wide-spaced train of impulses in frequency domain and vice versa? i want to know the intuition behind that.
1
vote
1answer
43 views

Third octave band zero-phase forwards-backwards Butterworth filter adds amplitude to complex signals?

Overall aim: to take a short signal (likely to be noisy with some tonal components) and filter it into third-octave bands (TOBs), apply frequency-dependent spectral adjustments, then recombine the ...
1
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2answers
1k views

How do I find the convolution of the following signals? [closed]

$h(t)$ is the inputted to convolve the $x(t)$ The signal written in unit step are: $x(t) = (5-t)u(t-3) - (5-t)u(t-5)$ $h(t) = 2u(t-1) - 2u(t-3)$ So to convolve I first change the function to: $h(...
1
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0answers
59 views

Underwater acoustic channel is giving me a flat BER vs SNR curve

I need to do OFDM and GFDM signal transmission in underwater acoustic channel. I have my underwater acoustic channel as follow. ...
1
vote
1answer
333 views

What is the relationship between the discrete time and continuous time variables?

While going through Proakis's Digital Signal Processing (page 21) ,he stated that if a continuous time signal $~x(t)~$ that has been sampled each $~T~$ seconds to produce a discrete time signal $~x(n)...
1
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0answers
40 views

Multitapering in time domain to obtain smoother filtered signals?

Suppose we want to approximate the instantaneous power $z(n) = |y(n)|^2$ of the discrete-time signal $y(n)$, where $y(n)$ is the result of filtering $x(n)$ with a given window $h(n)$, $y(n) = x(n) \...
0
votes
3answers
792 views

How to filter out everything but a single frequency in the time domain?

I'm new to signal processing and would like some insights about the best way to filter simple data without being too computationally intensive. I have an audio signal and I want to extract a single ...
0
votes
1answer
515 views

Impulse response (general form for linear systems as two-variables function $h(t,\tau)$) applied to Time-invariant systems

If a system is linear, then the operator $S$ mapping input signals into output signals - i.e. $y(t)=S\{u(t)\}(t)$ - is the integral of the input weighted by the impulse response: $$ y(t) = \int_{-\...
0
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2answers
79 views

Is there a way to use decimation or linear interpolation to shrink or stretch an audio signal in the time domain?

I am able to shrink/stretch an audio signal using Python code for a phase vocoder, as well as the stretchAudio function from Matlab's Audio Toolbox. Although both methods do indeed alter the audio ...
0
votes
1answer
46 views

Time domain representation of a modulated signal when symbol rate >> carrier frequency?

I need to understand the relationship between carrier vs. bits with PSK modulation, and what the signal in the time domain would look like if my symbol rate is far greater than my carrier frequency. ...
0
votes
1answer
114 views

Complex time domain signals and QAM

Is there an inherent connection between complex time domain signals and QAM? Given a complex time-domain signal is it always implied that this is a QAM-demodulated form of a real time domain signal? ...
0
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1answer
107 views

Converting a discrete real time domain to a discrete complex time domain signal

To test my understanding of amplitude modulation in the frequency domain I'm trying to replicate the center frequency with 2 side-bands in an Octave plot with the following code ...
0
votes
2answers
390 views

Intuitive meaning of complex time domain signal representation (quadrature sampling)

I saw What is the meaning of imaginary values in the time domain?. My question is about I Q samples as recorded from an SDR receiver (e.g. RTL-SDR). My understanding is that we can call these I Q ...