Questions tagged [fft]

The fast Fourier transform is an efficient algorithm to compute the discrete Fourier transform (DFT) and its inverse.

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Amplitude Matching for Exponential Swept Sine

I am working in the area of aerospace vibration testing and we use swept sine tests on structures and measure the response using the accelerometers. I tried implementing the technique "...
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DC Value of DFT

I came across this question and I've been pretty confused if its a trick question or I'm just wrong. Having a signal x[n] with 6 samples, it's DFT has values (6,3+j,0,0,0,3-j), what is the DC ...
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What is the point of smoothing an FFT or spectral density plot, and how does that affect the noise floor?

It appears that smoothing the FFT or spectral density plots of a noisy signal is a common practice. I see that common tools like MATLAB and Python have functions built in to their FFT tools to do just ...
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66 views

Is spectral density sometimes normalized by sampling rate rather than bin size?

I'm a scientist conducting an experiment that requires some signal processing. My expertise is not in signal processing, thus here I am. We've basically re-created an experiment conducted by other ...
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(Newbie question) Calculating the frequency spectrum

I'm quite new to this topic, with some basic knowledge however. I need to analyse an audio signal for different characteristics. Like the audio editor I use (an older Version of Audition, v.3) I would ...
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46 views

FMCW Radar - Range-Doppler Plot

The FMCW radar with the following parameters was implemented: ...
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31 views

Using MATLAB's Spectrogram Function for Analysis

In the documentation - sepctrogram(). Question 1)s = spectrogram(signal) and ...
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How to increase the resolution of the fft plot: Rule of thumb for generating good spectrograms

Is there a rule of thumb to generate a good resolution spectrogram ? I am currently blindly playing around with the parameters such as length of the signal N, ...
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Apply the Discrete Fourier Transform as a Matrix Multiplication in MATLAB

0 I have a vector x of length N x 1, I need to perform the iDCT operation for it using MATALB. I performed that using the below method: ...
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75 views

How to distinguish between FFT power leak or close frequencies

This week I was having an interview with a Professor for Grad School. He asked a bunch of questions related to signal processing that lead up to some questions about power leak on the FFT spectrum. So ...
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FFTW audio artifacts when modifying magnitudes in frequency domain

I'm currently working with FFT (FFTW3) that I'm using to apply treatments on audio files frequencies. The Forward/Backward test is passed, since I can get the exact same soundfile when processing ...
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Find the Equivalent Noise Bandwidth

I have already asked (in another thread) how to quantify (specify) the window function I have created. One figure I need it seems is the Equivalent Noise Bandwidth (ENBW) Or Noise Equivalent Bandwidth....
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Obtain Envelope and Pitch curves of my Singing Voice

I wish, in real time, to hum into a mic and produce via dsp the envelope and pitch of what I am humming, before outputting these two signals to my analog synth. This synth takes a gate and a cv signal....
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Is the DCT prone to spectral leakage like the DFT?

My understanding is that the DCT assumes the input to be an even periodic signal. This avoids the discontinuity that can occur in the periodic extension assumed by the DFT (see image). Does this lack ...
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How to specify a window?

I have developed my own window function for pre-processing signals prior to a DFT (FFT). How do I measure the performance of the window so that I can specify how good (or bad) it is? Maybe other ...
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66 views

Radar for Vital Signs – Matlab Simulation

Interested to design and simulate FMCW radar for Vital Signs sensing. The initial signal parameters are(1): When using the following Matlab code to generate the waveform: ...
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Decimation FFT Result

In my Signal Processing class we just learned decimation however after messing around in Matlab trying an example of decimation, I just can't understand what's happening. I get the introducing twi ...
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Why my signal is so noisy?

I have started analyzing a signal from a MEA experiment that consists of reading from electrodes inserted in a brain slice. Anyway, the signal is sampled at 2 KHz but the readings we have are very ...
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What does voices per octave means?

I was studying the description of continuous wavelet transform in Matlab and I came across this term '**cwt uses 10 voices per octave**' ...
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Denoising a Signal Project

I have recently started working on a project which aims to clean the noise from a signal that measures the concentration of certain chemicals. I am not an expert in signal processing, in fact, this is ...
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74 views

Correction of amplitude after zero padding for upsampling purposes

I have time sequence in which the data is sampled at 0.8 Hz. The data is related to chromatography (chemical analysis), that is why the sampling frequency is relatively low. The instrument cannot ...
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33 views

Computing Autocorrelation via FFT

I have seen several methods to calculate Autocorrelations using FFTs, and am confused about why they differ. Zero-Pad it to double its original length.Take the FFT. Then replace all the coefficients ...
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Arbitrary precision FFT and IFFT

For evaluating the performance of algorithms that use double-precision floating point numbers, or to pre-calculate double-precision floating point data to the best precision, it would sometimes be ...
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Why is it used the Power Density Spectrum (PSD) over an anylisis with the Fast Fourier Transform (FFT)? [duplicate]

I'm currently working with physiological signals (PPG and GSR) for emotion recognition but, from my research, I've found out that almost everyone in that area use a PSD analysis over a FFT analysis. I'...
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does a purely real FFT algorithm exist?

I am perfectly aware that you can efficiently use the standard FFT Cooley Tuckey algorithm to process N samples with one complex N/2 sized FFT. This however requires one additional loop before the FFT ...
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Why does sampling chirp at peak frequency yield correct frequency response?

Followup; setting Fs = bandWidth in accepted answer's code yields the "correct" frequency response of an LFM chirp: constant magnitude, parabolic phase. ...
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Exponential Swept Sine Distortion

I was able to get passable results on fundamental measurements using and exponential swept sine. Now I am trying to get distortion information from the same measurement but am puzzled by the results. ...
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Merge ECG with EMG data to form one signal using FFT

I was thinking of merging two signals, each with different units (one with BPM, other with mv), to form one single signal. For this, I thought of converting both the signals to frequency domain via ...
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121 views

Does chirp have constant magnitude frequency response?

Pg. 223 claims so, yet my results via DFT differ: Is the textbook wrong? My attempted explanations: (code) DFT vs DTFT: "frequency response" is computed via latter. Still, DFT should ...
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Noise and harmonic elements w/in a discrete time signal

So I have a discrete-time signal with around 300 samples. It is part of an environmental science application, so is not-strictly periodic although there clearly are periodic components. I have applied ...
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Translating SFFT expression to MATLAB code

The Symplectic Finite Fourier Transform (SFFT) of a 2D periodized sequence $x[k,l]$ with periods $(M, N)$ is defined as $$X[n,m] = \sum_{k=0}^{M-1} \sum_{l=0}^{N-1} x[k,l] e^{-j2\pi \left(\frac{mk}{M} ...
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30 views

nature of output of the addition of white noise with colord noise

I want to know that the addition of a uncorrelated time series x with a correlated time series, say y generates a time series ...
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167 views

Making the units of a analytically calculated PSD consistent with the units of an FFT

One thing that has always puzzled me is making the units of an analytically derived Power Spectrum Density (PSD) consistent with the units of an FFT. Let's say we record the output of a frequency ...
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35 views

Meaningfulness of Frequency Spectrum for Classification

I just started to dive into signal processing due to a free-time project. Therefore, this is my first question here, for which I searched many previous threads, but couldn't find what I was looking ...
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How much zero padding I should do to an audio signal before fft?

I was working on project and I need to do fft to my audio signal. I was going through a code and found following line. Can anyone explain me the line of code. ...
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how to plot fft with imaginary and real part in 3d or calculate the degree of rotation

I would like to make a plot like 1 and see the real and imaginary part in a 3d space. I dont want to make exactly the same plot. for me it is okay if i see the peak for both signals shifted. it is ...
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43 views

Cosine of amplitude 1 but GNU Radio shows FFT has amplitude > 30,000

I am doing an FFT on a cosine wave which has an amplitude of 1. The FFT is amplitude is not 1 but over 30,000. What am I missing here? It's from the GNU Radio FFT wiki page:
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EEG signal processing with wavelet or fft?

I have confusion about signal processing related with EEG signal. I have done some of my research and that made me more confused about processing and filtering the signal. Let me jump into the problem ...
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Using discrete chebyshev transform for spectrum analysis

From what I gather Discrete Chebyshev transform is used mostly in image processing. I was windering about speech recognition. I reviewed some papers regarding this point. Also, the Discrete Chebyshev ...
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60 views

Proving that FFT (and by extension any correlation based estimator) is unbiased

I have a pretty simple question which i should have been able to answer. Just wanted to check if people here have a better solution to it. I am trying to establish that FFT as a frequency estimator (...
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Identify consonant, phoneme from a given word

I'm new to speech recognition so apologies if the question sounds mediocre, I've started to read articles,blogs and research on sound recognition. They include topics like FFT, Power spectrum, filters,...
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60 views

What is the effect of wiping the right half of Fourier Transform bins?

I'm trying to change the pitch of a signal using a Fourier Transform (FFT) followed by an Inverse Fourier Transform (IFFT). I've found many examples, some of which zero out the right half of the real ...
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46 views

Produce PSD from a FFT output

I am using an FFT function in PHP language (https://gist.github.com/mbijon/1332348) which works very well, but cant produce PSD from its output: ...
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40 views

How to account for phase and shift when composing a new signal based upon 2 or more recordings?

I have 2 signals that were independently recorded, and want to produce a new signal that would represent what would be recorded if both signal sources were emitting at the same time together. ...
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Strange behavior in fixed-point FFT

This is a problem I encountered some time ago while doing my thesis, which still now, I am not sure to understand. By then, I was implementing the circular correlation in an FPGA using this Xilinx FFT ...
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59 views

Can you use Bartlett method in reverse? [closed]

I'm wanting to do an inverse Fourier transform. Can I use the Welch method to generate this inverse, by replacing the FT used within with an IFT?
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29 views

OFDM Modulation: what's the output of the FFT?

I'm trying to understand how OFDM is used in technologies like Wi-Fi. On the Wikipedia page, an idealized transmitter is presented with this schema: Data is converted from serial to parallel, mapped ...
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Implementation of Cepstrum in Python

Actually I want to denoise a signal. I know how can I implement FFT in python to denoise it. This is the implementation which I use(From this Kaggle notebook): But I don't know : How can I use ...
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100 views

How do I time-stretch a signal from the frequency domain?

I have $FFT(signal)$, and want to find $operation$ such that $$IFFT(operation(FFT(signal),2)) = timestretch(signal, 2)$$ Where $timestretch$ stretches the signal in the time domain - maintaining the ...
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FFT of shifted image in Numpy

I want to prove using numpy the theory of Fourier transforms in which translation in space corresponds to a shift in the phase domain (frequency domain remains constant). I have generated these three ...

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