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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Problems Using FFT to Compute Impedance in a Model Neuron

I'm a neuroscientist currently investigating the resonance properties of a single neuron model that a colleague and I have constructed. The language we code in is Julia, which I hope is similar enough ...
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Recover the first half of the time-domain signal of the N-point frequency domain signal using an N/2-point FFT

Let X be an N-point sequence in the frequency domain (where N is a power of two): $$ X = (X[0], ..., X[N-1]) $$ where $X$ is the complex and conjugate symmetric forward DFT of the real sequence $x = (...
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Practically Calculating Cramer-Rao Lower Bound

What is the method to compute Cramer-Rao lower bound for a particular application. For example I have an application in which FFT of an incoming signal is performed to get a Coarse estimate and then ...
Emerald_Waves's user avatar
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Audio sharpening

I'm working on a project where the purpose is to enhance FFT peaks in a signal (musical instruments), by other words, reduce non-harmonic components and enhance the identified FFT peaks. So far I'm ...
Filipe Pinto's user avatar
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1/3 octave spectra from fft

I have got a signal in frequency domain. This is a frequency response function from software, so I can do nothing about it and have to leave it in frequency domain. I want to transfer the data to 1/3 ...
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Extra 'fingers' found in graph after applying FFT in MATLAB

I am currently working on the FFT function in MATLAB. In this function, i require a 1024 number of data Time Domain plot and produce a 400 number of data Frequency domain plot. After applying the FFT ...
barryloh's user avatar
3 votes
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Artifact during this STFT spectrogram plotting

I am new to the field of DSP and I am currently working on implementing a real-time audio spectrogram using STFT technique. While making progress, I have encountered an issue when testing a constant ...
Sergio's user avatar
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Calculating THD vs. Frequency of an Acoustic System using the Exponential Swept Sine Method

I am working on analyzing the total harmonic distortion (THD) vs. frequency curve for an acoustic system. I am aware of the traditional method of exciting the system with a mono-frequency wave and ...
DSP novice's user avatar
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Improving the intuition for the 2d fourier transform

As far as I understand, the 2d fourier transform is calculated as following: ...
dmmpie's user avatar
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1 answer
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How to determine the CRLB for FFT based estimator with MATLAB?

I am trying to determine the CRLB for FFT-based frequency estimation in MATLAB. For this, I am simulating a single sinusoid in white noise with different amplitudes and constant noise power. Here is ...
Sparta's user avatar
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True Envelope algorithm: how to speed it up?

Premise (since somebody may ask about the background): I am the author of the spectral modules for SynthEdit, a modular framework for realtime STFT audio processing, currently struggling since ...
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Understanding convolution of Chirp z algorithm

I dont´t understand how works the convolution part of the Chirp z. I understand how the DFT is transformed \begin{align*} x(k) = \sum_{n=0}^{N-1} x(n) W_N^{kn} \end{align*} to this expresion: \...
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Solving the PDE of a signal in an optical fiber

Disclaimer Please let me know if this is not the right place to ask this question. Disclaimer Part 2 I have no background in signals. My focus is in mathematics. In my programming class, we are ...
3struck's user avatar
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Compensate for residual resampling error with a quadratic phase vs frequency- possible?

With regards to the answer in this post Is it possible to do deconvolution with two data sets that have different sampling rates? I suggest the possibility of compensating for a residual resampling ...
Dan Boschen's user avatar
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What's spectral "tilt"?

I am looking at article Speech-in-noise intelligibility improvement based on spectral shaping and dynamic range compression. In paragraph 2.2 the article mentions "tilt" of the spectral envelope. The ...
Danijel's user avatar
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Calculating Phase Response for 2 microphones given the input

I want to measure and compare the phase response of two identical microphones. To do this, I have a pressure chamber, which allows to apply the same pressure to both microphones. I apply a sweeped ...
user6522399's user avatar
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Why are the frequencies associated with the STFT bins not representative of the energy?

I'm experimenting with a 30 Hz sine wave and I want to extract the frequencies of this, and have implemented the algorithm to do so. This gives a correct reading, well, gives 29 Hz. I'm now wanting ...
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choosing windowing function for audio signal processing

Currently I am working on chord recognition, and get confused on several aspect. One of them is choosing windowing for reduce the spectral leakage. from what I read, hanning/hamming function is a ...
wendy0402's user avatar
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Points of interest in a spectrogram

We have several audio tracks, all of which are different versions of the same track under one type of distortion: the speed of the track is increased by a constant factor K (hence frequences are ...
Flavian's user avatar
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Compensate for standard deviation loss

I am not sure if this question will be a little off-topic on this forum, that I will give it a try anyway, since it implies signal process arguments. By using ...
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What is the proper way to select the time-bandwidth product when doing multi-taper spectral estimation?

Frequently programs for calculating the spectrum of a signal using the multi-taper method require the user to specify the time-bandwidth product. What considerations must be made when selecting the ...
slayton's user avatar
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Discrete Fourier transform in a multidimensional space

I want to measure the frequencies at which a point oscillates in a multidimensional space, let's take the example of a point on a 2d-surface. For now, I naïvely split the signal in two, along the ...
Emile's user avatar
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calculate root mean square, ratio of power, constant false alarm, ... of a signal

I am new to Digital Signal Processing, and am reading a paper. I don't know how they can extract some features from signal, like root mean square (RMS), Constant False Alarm Rate - CFAR, Mean Value ...
user1624637's user avatar
3 votes
1 answer
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Removing multiplicative noise (signal) in FFT

I've read up a little here on how to deal with multiplicative noise vs additive noise, with the most simple approach to take the logarithm of the signal to remove the noise. I'm wondering how this ...
user70478's user avatar
2 votes
1 answer
75 views

FFT Window question - high resolution windows

So I am pretty familiar with FFTs and FFT windows. I know that in general there is a tradeoff between mainlobe width and sidelobe levels. However, I recently stumbled across this discussion, where ...
Colin Marcus's user avatar
2 votes
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126 views

cyclic convolution: still have problems in understanding it correctly

I have the following scenario where there are 9 input boxes $S_{m\prime}$ and each box contain $L$ samples. I transfer the input samples of $S_{m\prime}$ to $G_m$ by multiplying and summing each ...
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Time domain frequency "loudness" isolation

There is a very useful tool in my DAW which allows me to isolate groups of "loudness" within the frequency domain. Basically, any bin greater than some min, less than some max. It makes it ...
Seph Reed's user avatar
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184 views

Fast DCT from DFT

I need to compute the DCT of a signal (in fact its a image). As I already have the DFT of that signal, I wonder if there is any cheap way to obtain the DCT in terms of the DFT. Note that I am not ...
Oier Lauzirika Zarrabeitia's user avatar
2 votes
0 answers
92 views

How to sum amplitudes only without distorting the signal?

I do audio signal processing using Python (scipy, numpy etc.) I'm trying to "mix" 2 audio signals in a way that reduces phase canceling as much as possible. So I do an FFT of the 2 signals, ...
hastoy's user avatar
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For a real-world system of oscillating mechanical components, what kinds of frequencies should I seek in DFT?

I have a real world system I am analyzing consisting of actual mechanical components that oscillate by rotating back and forth in a fixed axle (kind of like those finger fidget spinners but my system ...
LobsterMan123's user avatar
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154 views

Different result between numpy.fft.rfft and scipy.signal.freqz

I'm using the following two functions to calculate the frequency response of an impulse response: numpy.fft.rfft and ...
DSP novice's user avatar
2 votes
0 answers
122 views

How to improve my FFT output?

I am to reproduce the figure below but with a different blue line (source), which shows the ideal normalized frequency spectrum (grey) of a spectral ripple with 0.7 ripple-per-octave and an electric ...
NonIntellego's user avatar
2 votes
1 answer
195 views

In what cases can you get aliasing below the Nyquist frequency?

I took the one-sided FFT of a signal and plotted up until the Nyquist frequency. Then, I took the real part of this FFT multiplied by $i\omega$ following a calculation that I'm trying to do of a ...
user avatar
2 votes
0 answers
288 views

Frequency Interpolation of DFT to create Zero-Padded IFFT

As a response to this question I have proposed interpolating new samples in a DFT (meaning the frequency samples of an existing DFT result) sufficient to be the new samples that if we were to take the ...
Dan Boschen's user avatar
2 votes
0 answers
153 views

Multiple 1D gaussian filter

Given $$ \begin{cases} &f_0(x)=1 \\ &f_{n+1}(x)= (\varphi*(f\mathbb{I}_{[a_n,b_n]}))(x)=\int_{-\infty}^{+\infty}\varphi(x-t)f_n(t)\mathbb{I}_{[a_n,b_n]}(t)dt = \int_{a_n}^{b_n}\varphi(x-t)f_n(...
NN2's user avatar
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How do large tap counts effect FIR Filters for block data?

I am using the ARM CMSIS DSP library for a signal processing application. I find good filter performance when using tap counts that are in excess of 10% of the length of my data block. I understand ...
FooAnon's user avatar
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2 votes
0 answers
143 views

How to compensate the energy of a spectrum after using a Tukey window

I am trying to minimise the noise in a spectrum of a variable. I have divided the time history in equal parts, I have multiplied every part of the time history by a Tukey window, done a FFT of each ...
Luca Mirtanini's user avatar
2 votes
0 answers
161 views

Blow sound recognition without using machine learning

I am building an experience in Unity that will recognize when a user blows into the microphone. I have a working implementation that recognizes sounds above a certain loudness threshold, but I want to ...
Anya 's user avatar
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2 votes
0 answers
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Understanding Phase noise of a Hard Limited Sine Wave

I need help in understanding the frequency spectrum of a sine wave with phase noise that has been hard limited. Background: Typically, textbooks define phase noise for a sinewave, however in many ...
Nimit's user avatar
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2 votes
0 answers
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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 ...
Olli Niemitalo's user avatar
2 votes
0 answers
168 views

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 ...
danipascual's user avatar
2 votes
0 answers
1k views

How to take the inverse FFT of Welch's power spectral density in Python?

I have calculated the power spectral density of a weakly-stationary signal using Welch's method (as implemented by scipy.signal.welch in Python), and am looking to take the inverse Fourier transform ...
T. Zaborniak's user avatar
2 votes
0 answers
245 views

fft formula convention

I try to code up an algorithm from a scientific paper where they solve a differential equation using Fourier transforms. In the paper, they use the FT convention $\rho(x_i) = \sum_{k=-m}^m r_k e^{i2\...
reloh100's user avatar
2 votes
0 answers
196 views

Correct way of derivating in frequency domain with FFT

I believe I am very close to the answer and only need a small nudge to get to the answer. What I want: I want to take a signal, use FFT to transform it to the frequency domain (FD), multiply it by $...
Harry Svensson's user avatar
2 votes
0 answers
249 views

Frequency resolution - resolution BW relation for different window functions

I am working on FFT based spectrum analyser and I am not sure how to proceed calculating the RBW. According to the document (page 20) in the link, RBW described as $k \frac{f_s}N$ where $f_s$ ...
MertK's user avatar
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2 votes
0 answers
400 views

Frequency translation with FFT

I'm new to DSP and I would like to make an SDR receiver. For this I want to shift bins in the frequency domain in order to bring to 0Hz any portion of the base band spectrum (I know that there are ...
BlackSun's user avatar
2 votes
0 answers
82 views

Selection of transforms, windows, wavelets for current signal analysis

I am new to this topic but I already read about the propperties of different signal analysis methods. I am stuck with the obvious advantages of FFT, STFT and Wavelet transforms but can't find good ...
dopetob's user avatar
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2 votes
0 answers
525 views

Decimation and Upsampling

I'm currently trying to understand decimation and possible ways to retrieve back the original signal. If the signal of supposed frequency $X$ Hz was decimated by a factor of four, would there be $4$ ...
ntmt's user avatar
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2 votes
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112 views

DFT of signal with frequency-dependent time shift

I have a signal $s[n]$, and I want to compute the DFT of it with a frequency selective shift (computing all $k$ here but I really only care about $k > 0$) $$S[k] = \sum_{n=0}^{N-1} s[n-\dfrac{N}{...
gct's user avatar
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2 votes
0 answers
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Is there a way to extract the difference between the 2 signals? Fitting?

I'm very new to signal processing and have been struggling this far. I have a device that measures the signal due to the magnetization of iron particles. In order to calculate the response of the ...
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