Questions tagged [frequency-domain]

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Constructing frequency domain filter from a 2d spatial kernel

Given a 2d spatial kernel $h$, I want to construct the corresponding frequency filter $H$. In theory, $H$ is simply obtained by calculating the DFT of $h$ using a FFT algorithm. But in practice, there ...
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3answers
3k views

Comparison between 2 images in Frequency domain

As you can see there are 2 images from the Tom and Jerry cartoon program. In the 1st image both Tom and Jerry are present. But in the 2nd one,only Tom is present.Now,we can clearly see this ...
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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 ...
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3answers
2k views

What does the negative sign mean in the image frequency domain?

When I transform an image from the spatial domain to the frequency domain, some frequencies are negative. What is the meaning of the negative sign? For example:
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3answers
5k views

Impulse Response to Frequency Response in Octave

Having an impulse response of an audio system recorded as a wav file, how to calculate the frequency response of the system with octave?
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1answer
2k views

Performing classification based on FFT results

It is perhaps important to start with the fact that I am a complete beginner in DSP. I have got a number of audio recordings (of sampling rate 22 kHz) - of bird songs - which I have been trying to ...
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2answers
2k views

Extract frequencies from PCM signal

I have an PCM (pulse-code modulation) signal. If I want to work out the frequency of a sample $ x $ long, I count the number of peaks/troughs of the sample, and divide by $ x $. The equivent dB of ...
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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 ...
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2answers
83 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} = (...
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1answer
1k views

How to calculate a delay between two signals in frequency domain?

Calculation of a delay between two signals is generally done by finding the maximum in the cross-correlation of the two signals (in time domain): $$ \tau_{delay} = \arg\max_\limits{t}(f(t) \star g(t)) ...
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1answer
418 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 ...
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3answers
1k views

Reflecting negative frequency to positive frequency

I am trying to synthesize sinusoids by using window function in the frequency domain. It involves: In frequency domain, shift the window to center around the peak frequency To generate a DFT frame, ...
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2answers
15k views

Convolution in the frequency domain

We often hear that "convolution in time is the same as multiplication in frequency", and vice versa, that "convolution in frequency is the same as multiplication in time". So in a typical windowing ...
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1answer
4k views

frequency domain phase shift

While going through FFT I came to know that, shifting of phase in frequency domain results on shifting of time in time domain. According to this, in wireless communications, from the transmitter side ...
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1answer
182 views

How to distinguish between the different frequency domains?

Sometimes the terms 'Fourier domain', 'complex frequency domain', 'Frequency domain' and 's domain' are used interchangeably. Take those answers here for example: http://answers.yahoo.com/question/...
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1answer
116 views

Designing a Chirp in the Frequency Domain

I am trying to create a chirp signal in the frequency domain, by simply setting the magnitudes of each frequency bin to one, and then setting the phase delay function such that the resulting time ...
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2answers
227 views

Proof of fourier transformation of multiplication of two signals

I've been trying to find a proof of the following, but still I m unable to proof it, can someone help me? $$ ℱ[x(t)g(t)] = \frac{1}{2\pi} [X(\omega)*G(\omega)] $$
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1answer
1k views

Meaning and unit of frequency in Laplace (Fourier) transform

Imagine transfer function obtained by Laplace transform, for example: $G(s) = \dfrac{1}{s+1}$ Now, I would like to do some frequency analysis, so I replace the $s$ with $\omega i$ (let's consider ...
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2answers
1k views

Compressing a time-domain signal in the frequency domain Matlab

I'm new to frequency domain analysis. Let's say I have a frequency domain representation from a time domain signal. What I want to do is taking frequencies with a low amplitude out of this frequency ...
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1answer
73 views

Stability varying with order

I have been doing some research into modelling acoustic spaces, and (with help from this site) I've managed to take the frequency response of fibrous layer model, convert it to a reflection response ...
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1answer
84 views

Dealing with bias in an FFT for frequency correction

I'm working on using an FFT for frequency correction of a generic modulation signal. My algorithm basically attempts to balance the energy in the positive and negative frequencies of the FFT to be ...
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1answer
500 views

get poles and zeros of frequency response

I am working on a python based LTSPICE project. I would like to get poles and zeros of AC simulation data. Is there a way to get them under use of the magnitude and phase out of the frequency ...
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1answer
2k views

Extract frequency data from MP3 file

I want to do frequency analysis of audio data, basically trying to figure out what the notes are in a song algorithmically. The standard approach is to decode the MP3 into PCM data and run it through ...
2
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1answer
384 views

Purpose of multiplying fft output by Hann window?

I'm working with some acoustic propagation models at the moment. A feature I've noticed in 2 of these models is that the output of the model is often multiplied by a Hann window in the frequency ...
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1answer
1k views

Normalized cross-correlation in frequency domain

I never worked with signal processing and never really used Fourier transforms before, still I am working on a project consisting on taking the output of an accelerometer to detect some movement ...
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1answer
310 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 ...
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1answer
232 views

Convolution Offset and Factor in Frequency Domain

See this link. The following Convolution in Spatial domain code is written in C#. ...
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1answer
113 views

FFT radix-2 in audio - resolution issues - logarithmic scale - sample rate VS buffer size

I would like to ask how to deal with audio DSP. Is FFT good at all to deal with audio? I am working on an app, that generates a single impulse, rout it to an EQ plugin, and the output of the plugin is ...
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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 ...
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3answers
379 views

If a square wave is a sum of odd harmonic impulses, why is it continuous in the frequency domain?

A square wave is a sum of sinusoids so surely it should be represented as individual discrete impulses in the frequency domain, where all other frequencies are 0. Why instead are those intermediate ...
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2answers
152 views

Fourier transform of $ne^{-an}u[n]$

I need to find the Fourier transform of the following signal: $$ne^{-an}u[n]$$ The answers start by using the rule of the basic signal: $$a^nu[n] \rightarrow \frac{1}{1-ae^{-j\omega}} $$ and then ...
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2answers
4k views

Fourier series - time and frequency domain confusion

I am computing the fourier series of the following function between $[-0.5, 0.5]$ $$\displaystyle f(t) = \frac{1}{2} - |t|$$ According to the definition of Fourier Series the coefficients are given by ...
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2answers
127 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 ...
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2answers
284 views

Showing linear-phase frequency response when only real part is known

I'm studying for an exam, and this particular practice problem is missing the solution: Given a causal LTI system where only the real part of the frequency response is known, $$\Re\left\{H(j\...
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2answers
8k views

Understanding the frequency domain [duplicate]

I'm trying to understand what frequency domain is. I found general explanations on the Internet, for example: frequency-domain graph shows how much of the signal lies within each given frequency band ...
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3answers
714 views

How should this fft output be intepreted?

I am currently reading some code, so I can understand how this FFT output is actually been stored. I have a function which computes FFT of audio file, and stores is in the format. ...
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2answers
2k views

What is relationship between entropy and frequency in image

When I was studying spatial frequency and entropy, it occured to me that "is there a relationship between entropy and frequency?". As you can see, if we consider only horizontal line, the frequency ...
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1answer
171 views

Absolute value based AM envelope detection viewed in the frequency domain

In my understanding when a passband AM signal is demodulated with an envelope detector taking the absolute value restores the original baseband version of the signal and the low-pass filter removes ...
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2answers
189 views

Is the value of a frequency bin of a DFT-output the average of the 'real' frequency values within that bin's range?

I am wondering whether the value of a frequency bin with a certain resolution is the average of the fourier transform values of the 'real' frequencies within that bin's range.
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2answers
478 views

Closest two frequencies that can be resolved

Forgive me if I misuse the terminology. I wish to transmit two slowly changing analogue signals by amplitude modulating two higher frequency sinusoidal carrier waves. I will superimpose the two AM ...
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1answer
495 views

Can I use frequency hopping spread spectrum technique for audio steganography?

I have been trying to use spread spectrum technique for audio steganography. I read a lot about it.But i didn't find any information about the steganography scheme using FHSS(frequency hopping spread ...
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1answer
563 views

Why multiplying frequency kernel with sinusoid results shifting frequency domain

I am having great time while reading "The Scientist and Engineer's Guide to Digital Signal Processing" book. In "Chapter-14 Introduction to Filters" author indicates we can create high pass filter ...
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1answer
220 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 ...
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1answer
65 views

Estimating the SNR of 2-FSK

I have some iq data recordings of a 2-FSK waveform that I've created periodograms from. How do you estimate the SNR of this waveform in the frequency domain? I've heard two opinions: One: Integrate ...
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1answer
763 views

Why is the size of results from FFT half the size of the input, while that is not the case in image processing?

When dealing with real data, Fourier Transform produces symmetric results and FFT algorithms discards half of it. An input with 1024 points will yield only 513 points in the output. However, in image ...
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1answer
158 views

What's the frequency transform of a random matrix?

Assume the following: img = 255*rand(512); %Generating a 2D matrix with random numbers between 0 to 255. fftimg = abs(fft2(img)); %FFT of the image. The frequency transform of this image is a ...
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3answers
1k views

How to get Instantaneous Magnitude for a Instantaneous Frequency From FFT?

My understanding if a frequency in my signal doesn't line up exactly with a bin, it is smeared over a few bins to the right and left. How can the instantaneous magnitude be determined? (do I have to ...
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1answer
58 views

Measuring frequency response with white noise signal

I need to measure a frequency response of an eleсtric circuit (simple like an RC-filter). I suppose that I can generate an input signal that has spectrum like white noise (for example, m-sequence ...
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1answer
44 views

The cost function of LS algorithm

I'm trying to understand the derivation of LS algorithm for channel estimation in OFDM. Could anyone explain why do we need complex conj transpose in the below equation?
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4answers
256 views

Remove brighter regions in an image on frequency domain

I'm newbie and maybe this is not the right place to ask this question, or this question has no sense. I'm very interested in working on filtering images on frequency domain. I have found a few ...