# Questions tagged [signal-analysis]

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4k views

### DFT vs FFT: does odd number works for DFT only?

I am always confused between FFT and DFT. In both algorithm, it has been assumed that the signal is periodic (so my understanding is that, if you have a 20 sample point signal, and you do DFT or FFT, ...
1answer
5k views

### How do I generate sound using MATLAB?

I want to generate and play sound for tones with frequency 100 Hz and 200 Hz for 10 sec and 5 sec respectively using MATLAB with sampling frequency equal to 20500 Hz. Also I want to plot their ...
2answers
10k views

### What is the difference between a one dimensional and a two dimensional signal?

If a signal depends on only one variable then we call it one dimensional, and if a signal depends on two variable we call it a two dimensional signal. But when we represent an one dimensional signal, ...
3answers
258 views

### How to determine, calculate and plot a probability distribution for a given set of numbers?

A device is rotating with a particular wind speed and producing such pulse frequencies in a minute: ...
1answer
128 views

### Right algorithm for fourier transform on physical heights

I have data from a LIDAR unit that I would like to get the spectral density of. Unfortunately, the only thing I remember from my Fourier analysis class are the methods that I know will not work. The ...
3answers
546 views

### Signature of a Signal for anomaly detection in Power Systems

I am a power systems engineer and am doing preliminary leg-work for detection of a specific anomaly in power systems that cause the observed waveform to be distorted. False positives are somewhat ...
2answers
159 views

### How to calculate the Fourier transform of absolute-valued sinusoid?

The signal $x(t) = |1+a\sin(\omega t)|,(a>0)$ is a continuous waveform. In order to extract the frequency parameter $\omega$, I conduct the FFT of it and obtain its spectrum showed as follows. The ...
1answer
389 views

### Is there such a thing as a moving bandpass filter algorithm?

I am looking for an algorithm, preferably available in a Python library, which passes only frequencies of interest, with the center frequency continuously changing as it moves through an array of ...
4answers
1k views

### Relation between curve fitting and filtering

Before I ask the question: I am from mechanical background and would appreciate a detailed answer. Generally, for automobiles, I am trying to understand the following: Given, say $1\;\mathrm{sec}$ ...
1answer
103 views

### What subclass of nonlinear systems can be represented by Volterra series?

Can every possible nonlinear time-invariant Volterra series be represented by a Volterra series? If not, which ones can? Also, are there any time-variant systems that can be represented by Volterra ...
2answers
116 views

### Useful natural “Hilbert-like” $n$-uples and $n$-fold "analytic signals

If $\mathcal{H}$ denotes the Hilbert transform, the analytic signal of a signal $x(t)$ is $$x_a(t) = x(t) +\imath \mathcal{H}(x(t))\,.$$ The real and imaginary parts form Hilbert pairs. Are there ...
1answer
313 views

### rtlsdr sample rates and nyquist rate

I have a rtlsdr dongle which apparently has a max sample rate of about 2.4 MHz. I'm wondering how it's possible to capture signals at say 900 MHz with this device. Doesn't the sample rate need to be ...
1answer
734 views

### How moving part pixel intensity values of video frames becomes dominant compared to stationary part intensities in reconstructed frames?

Hello everyone i want to do dynamic texture video sementation using the Fourier transform in MATLAB. I am applying 3-D fft on dynamic texture video frames (using matlab function 'fftn') and ...
2answers
103 views

### Dealing with echoes / dead-spots in digital transmissions

I'm looking at communicating digital data through the air as soundwaves. To illustrate the problem, I generate a 10-cycle 2kHz wave, play it out through my MacBook's speakers and pick it up on my ...
3answers
2k views

### Filtering with STFT

I have sucessfully implemented a STFT (+inverseSTFT with perfect reconstruction of original signal, with overlap add, etc.) in order to work on audio files. Using this STFT / iSTFT framework, I have ...
2answers
3k views

### How does transition width of a low-pass filter affect a message which is well within the pass-band?

I'm taking a communication systems course and we use GNURadio in the lab. In an exam, we had a simple question where we were asked to demodulate a Dual Side Band (with carrier) AM signal in GNURadio. ...
1answer
139 views

### Trying to write a signal “unsmoothing” algorithm

Up front: I'm just a hobbyist, and I know zero about signal processing; I'm trying to write a simple(?) javascript algorithm and hoping I don't need a PhD in DSP to make progress on it. I have an ...
1answer
629 views

### what are the Pros and Cons of ESPRIT and MUSIC algorythms?

On wikipedia there are only 2 lines about ESPRIT: Estimation of signal parameters via rotational invariant techniques (ESPRIT)... MUSIC doesnt have an entry in the music disambiguation page, other ...
2answers
635 views

### FFT of SIN waves with different phase delays

I have come across a peculiarity of FFTs which has got me somewhat baffled. I've simply summed up 101 sine waves and taken the FFT using this matlab script : ...
2answers
689 views

### Response of a system to a step function (heaviside)

I'd like to compute the response to a step function of a electrical/thermal system. Generally I can "easily" compute the transfer function $H$: $$H(\omega) = \frac{V_{out}(\omega)}{V_{in}(\omega)}$$ ...
1answer
2k views

### What is the reason for filtering out the negative frequencies of a signal?

I am reading this tutorial. Quoting the lines from the topic "Analytic signals and Hilbert transform filters": the corresponding analytic signal $z(t)=x(t) + j {\cal H}_t\{x\}$ has the property ...
2answers
1k views

### How to identify useful elements of audio recording and ignore lulls?

I assume this is a relatively simple DSP task, but I'm having trouble finding any information on how to approach my problem. Hopefully someone with more experience and brain power can help me out: I ...
2answers
2k views

### Effects of DC offset on a signal

What are some of the reasons why DC offset is considered undesirable for a timeseries signal other than wastage of power during transmission ? Specifically, How does it cause spectral leakage and out ...
1answer
72 views

### Variance of an Implicit Function of Kalman State Vector

Given a state vector given by $x = {[r, v, a]}^{T}$ (Range, Velocity, Acceleration) the Time to Hit is the the time which holds the following: $$r + v {T}_{tth} + \frac{a {T}_{tth}^{2}}{2} = 0$$ ...
2answers
501 views

### Comb-like peaks in frequency spectrum

I am currently working on a project which involves measuring the sound produced by the onset of a vapour bubble in boiling water. All the experiments went perfectly well and I'm now trying to obtain a ...
1answer
6k views

### Concept of Orthogonality and Orthonormality

Please explain me the concept of Orthogonality and Orthonormality. I understand that the mathematical definition of orthogonality between two vectors is that their dot product is zero. It means that ...
3answers
1k views

### Need a better step detection algorithm

I have a time series with lots of steps/jumps (data file here). A plot is given below. I would like to subtract an appropriate value for each of these square wave features to bring them back down to ...
1answer
357 views

### Determination of periodicity in data and finding mean

I have to find whether there is any pattern (I mean periodicity or close to periodicity) and if there is, for one cycle i have to perform numerical integration to determine mean. In the first picture ...
2answers
2k views

### An explanation of parts of the MUSIC Algorithm for someone without a background in signal processing?

I've been looking at every tutorial and paper I can find, but I keep losing the intuition behind what's going on when they get into the matrix operations. There is a step in which the signal vector ...
2answers
82 views

### Need to calculate $\frac{E\left[|x(n)|^4\right]}{E\left[x^2(n)\right]}$

I need to calculate $\frac{E\left[|x(n)|^4\right]}{E\left[x^2(n)\right]}$ in real time, where $x(n)$ is complex. For $E\left[|x(n)|^4\right]$ I plan to take the absolute, raise it to the power $4$ ...
1answer
2k views

### Large Laplacian Spatial Filter on EEG?

I want to know that why large laplacian spatial filtering is done on EEG signals? I tried a lot but could not find material on LLSF. And what is meant by spatial filter ( in context of Digital Signal ...
4answers
7k views

### what does the statement “band limited signal of 5 KHz” mean

A band limited signal of $5$ kHz is observed at the output node whose sampling frequency is $600$ kHz. What is the minimum order of the filter? Does it mean: a signal that is from $0$ to $5$ kHz on ...
1answer
45 views

### How to match two signals that have similar shape but are scaled and expanded?

I have two signals A and B in time domain as follows: Visually both signals look very similar; however the X and Y axis range are different for both the signals. Signal B is basically a "stretched" ...
1answer
53 views

### Compare two signals, find times when they are affected by the same processes

I have two (noisy) signals $S_1(t)$ and $S_2(t)$. They contain information on three distinct events occurring in a physical system. Event $A$ affects only $S_1(t)$, event $B$ affects both $S_1(t)$ and ...
1answer
65 views

### What is the signal-noise model of laser induced fluorescence?

The following image is an example of a fluorescence signal trace from the photomultiplier tube detector (PMT). Each spike represents one fluorescently labeled cell. This signal model is definitely ...
1answer
2k views

### Calculating SNR from Frequency Domain

As I am newbie to signals, I have collected an appliance signal in frequency domain as follows: (PSD- Power Spectral Density). So, I need to calculate the SNR (Signal to Noise Ratio) and BER (Bit ...
1answer
207 views

### Efficient FFT (or SFFT) for adjacent parts of signal with overlap?

Imaging we have a signal $x$, which is segmented to 50% overlapped vectors $x_1,x_2,..,x_m$ , and we intent to compute FFT of each segment. Is there anyway that we can reduce computation of FFT of ...
1answer
49 views

### How to differentiate the product signal $f(t)\theta(t)$, where $\theta(t)$ is Heaviside's unit step function?

What is the derivative (in the engineer's sense) of the causal function $f(t)\theta(t)$, where $\theta$ is the Heaviside unit step function? I've seen the formula $f'(t)\theta(t)+f(0)\delta(t)$, ...
1answer
356 views

### Occupied Bandwidth

I am pretty new in the field of Signal Processing. I am a structural engineering graduate student at the UT at Austin. I am currently working on a project that regards acoustic emission monitoring of ...
2answers
245 views

### Is it correct to subtract two signals acquired over different times and trials to remove the common signal in them?

I have two signals that represent the response of a neuron under two different conditions. Signal 1 (S1): response to Stimulus A Signal 2 (S2): response to Stimulus A+B The response to stimulus A is ...
1answer
342 views

### Can someone let me know linearity, time-invariance, causality, memory characteristic of the system?

The input/output system is $$\frac{dy(t)}{dt}+2y(t)=2x^2(t)$$ I want to know this is linear? causal? time-invariant? memoryless? According to solution, the answer is 'Linear if zero initial ...
3answers
2k views

### Removing unwanted square-wave noise from a signal

I have a signal, s, given at the end of this message. I need to remove the square wave shape from it. The desired signal is actually very small and it has been contaminated by a strong square-shape ...
1answer
1k views

### Separating 'signal' from periodic 'noise'

I have data in which the signal we want is a few gaussian peaks superposed on a noisy background in which some of the 'noise' is periodic. Simply suppressing the associated fourier modes is effective ...
1answer
247 views

### Usefulness of Matrix Notation for Linear Periodically Time Variant Transformations

I am quit puzzled about a notation I found in Gardner's 1986 book titled Introduction to Random Processes. It is in the chapter on Cyclostationary Processes at section 12.4 which pertains to Linear ...
1answer
340 views

### Estimate the Discrete Fourier Series of a Signal with Missing Samples

Assuming we have a discrete signal ${ \left\{ x \left[ n \right] \right\}}_{n = 1}^{N}$. Which has a Discrete Fourier Series. Now, assume I'd like to estimate its Discrete Fourier Series ...
2answers
1k views

### Using Goertzel Algorithm in under-sampling

I plan to calculate a signal's phase using Goertzel Algorithm. I have 2 signals coming to microcontroller's ADC. Need to measure the phase difference between them. Signals are 15MHz sinusoids. Sample ...
1answer
263 views

### What is the general feature of a time domain signal that gives a step like spectrum?

I'm trying to study a nonlinear system by sending a pulsed signal into the system and look at the response spectrum. The signal I send to the system is something like and the response spectrum from I ...
1answer
174 views

### Noise rejection / feature extraction

I'm hoping someone could point me in the direction of some signal processing methods to clean up my data. I'm collecting physiological data from human muscle (lower leg; gastrocnemius) during walking/...
1answer
939 views

### Why do we read that Hilbert transform can be used for envelope detection?

We can often read that Hilbert transform is useful for envelope detection (e.g. Hilbert transform to compute signal envelope?) I have done some tests with various soundfiles, and ...
1answer
181 views

### Phase Modulation and Intermodulation Anomaly ? (Spectrum plots inside - **Updated**)

I have a MATLAB script for modelling a two tone signal (a sum of two sinusoids) going through a non linear transfer function (such as an amplifier). The amplitude of a signal is amplified non linearly,...