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

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Is matlab fft faster for real input?

I realize that matlab fft is twice as fast for real input. But does matlab fft take the fact that the transform will be conjugate symmetric into consideration? Since the input is real, it would have ...
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1answer
26 views

Do all Harmonics of a periodic sound start from a 0 base

I've been thinking about additive synthesis and I'm wondering if all sounds begin at (theoretically) phase 0?
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1answer
24 views

Matching headphone responses

First post, and this isn't my field of study, but I'm giving this a go anyway: My latest endeavor is to use a bit of DSP magic to match up various pairs of headphones, at least in terms of their ...
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1answer
20 views

what is the preffered data and FFT length for blackman harris window for improving Accuracy due to ENBW Consideration of window?

for Rectangular window if data length is 1K then FFT Length Should be 1K FFT only because ENBW of rectangualr window is 1.0 but for Minimum 4-Sanple BlackmannHarris window is 2.0. so for improving ...
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2answers
42 views

applying single pole filter to simple signal

How to apply single pole filter to simple signal fs = 500; ts = 1/fs; t = 0:ts:1-ts; fc = 50; S = cos(2*pi*fc*t);
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18 views

Correlation of an image in the Fourier Domain

I have been reading up on correlation in the frequency domain, and I just had two questions which I could not find in the book I was reading nor online: [1] So correlation is the same as a normalized ...
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21 views

Sound Characterization [on hold]

For the last 6-7 months I have been working on a small project attempting to get sound-recognition to work on a raspberry pi in real time. My last iteration of sound recognition was centered around ...
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2answers
31 views

Frequency response of a (rectangular) integrator

A very simple question which can't really figure out: I have a simple discrete time rectangular integrator with Z transform H(z) = 1/(1-Z^(-1)) Plotting the frequency response with Matlab using ...
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1answer
32 views

Is real-time Hilbert envelope feasible?

Is the Hilbert envelope (analytic signal) feasible to be calculated in audio frames/blocks in real-time, when using FFT with windowing. What I'm specifically concerned with is that how does it not ...
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10 views

calculate value at t=0 (python)

After generating sine wave: ...
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1answer
15 views

Amplitude of an image

If I take a two dimensional image and conduct a fourier transform on it, I would get a two dimensional matrix of complex values. If I want to find the amplitude of each value, is that the same as ...
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2answers
42 views

Zero phase in IFFT

I'm trying to synthesise a sine waveform and I'm noticing that if I perform the IFFT with the Sine aligned to a bin frequency the phase is zeroed, however if I tune the sine off of the bin frequency ...
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1answer
40 views

Is it appropriate to use PSD on the analysis of a plucked guitar string?

I'm using python 2.7 to compare tonal differences in guitar stings. I've found that in matplotlib, there are some great built-in features such as matplotlib.mlab.magnitude_spectrum and ...
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3answers
56 views

Using FFT as a channeliser

This article mentions that the DFT/FFT can be used as a channeliser in a similar way to a filterbank. I get how the DFT filters into spectral bins, but its output is in the frequency domain, i.e. ...
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2answers
53 views

MATLAB : How to filter a data signal

I have a data signal (column vector) with N values taken over at specific sample rate (dx) at a fixed frequency. After taking the Fourrier transform of this signal and representing it in the Fourier ...
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2answers
143 views

Power spectral density vs. FFT bin magnitude

What's the difference between these? Both are measurements of some form of signal power, but surely there's some difference between the power they are measuring?
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0answers
25 views

Dynamic range compression in the frequency domain?

I'm trying to do frequency-band specific dynamic range compression (like multi-band compression) and was thinking of whether dynamic range compression is doable in the frequency domain or whether it's ...
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1answer
35 views

How to interpret these FFT results?

I have recently started to use MathNet.Numerics, and one of my needs is to perform FFT analysis of Electromyographical signals. The first test I did was to get some 15 seconds of signals at 2kHz, ...
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1answer
29 views

Why 1536 FFT size for 15 MHz in LTE

Why we use 1536 point FFT for 15 MHz bandwidth, when we can use 1024 point FFT, as in bandwidth of 15 MHz we have only 900 subcarriers.
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28 views

noise in signal

I am trying to add phase noise in signal. However, when i see the graph in frequency domain the spectrum is not broading. Can anyone tell me what mistake i am making? ...
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1answer
96 views

Why is the magnitude of the second component of my FFT spectrum always the largest one?

While working with FFT, I have a strange case with a current experimental setup. I am working with beat frequencies (intermediate frequency output) and using a standard FFT algorithm (complex to ...
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1answer
55 views

Baby Cry Sound detection

I wanted to write a code to detect baby cry sound. I am using Windows as platform. Presently, I am able to get audio samples and its frequency plot(using FFT) but not sure how to proceed forward. I ...
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1answer
70 views

Efficient FFT computation of a zero-padded vector

I don't think this question has a good answer but will ask nevertheless since it has been bothering me for a few days. I am interested in computing as efficiently as possible the N-point FFT of a N/2 ...
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19 views

Normalized Cross Correlation in Frequency Domain Windowing for Object Tracking

I'm implementing a normalized cross correlation algorithm in frequency domain on a DSP for object tracking. I have a search window and a reference window. Both windows are zero padded to accommodate ...
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1answer
46 views

Detecting a specific pop in a real time audio signal

I am listening for a very definite pop in a real time audio signal. So far I have managed to get the audio signal in at a sampling rate of 44100.0 Hz and 2048 frames per second. I have visualized the ...
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1answer
47 views

What is the meaning of imaginary values in the time domain?

Say I take a real valued function in the time domain, take the Fourier transform to get its frequency domain representation, do some work on it in the frequency domain, which leads to imaginary ...
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0answers
25 views

Curve fit for fft dplot

I have data from accelerometer (time domain) and convert it to fft using Fourier Transform. However, I need to do the curve fit to the plot. Can somebody share with me the coding.I don't know how to ...
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1answer
122 views

Does our brain constantly ifft to hear?

From my understanding our ears have hairs/cilia in the cochlea that resonate at frequencies within our hearing range. To me this means we are hearing in the frequency domain as opposed to the time ...
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2answers
75 views

Interpreting the FFT results of a structural vibration problem

System: Cantilever beam type models, with an accelerometer on the end. The beam base is excited at various frequencies in harmonic fashion on a shake table. This results in vibration in the beam. The ...
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1answer
38 views

Real-time frequency recognition in python

I'm a newcomer to signal processing, so forgive my ignorance. I'm working on a project in Python that will play a .wav file and pick out the dominant frequency as it plays. I've found a few examples ...
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1answer
40 views

Period, amplitude and phase through FFT in MATLAB

I need to compute period, amplitude and phase of the signal from spectrum analyser. It looks like a sine wave. Since i am new to MATLAB and also have limited idea about Fourier transforms, I am ...
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1answer
49 views

Difference between real fft and complex fft with imaginary part of zero in fftw?

I have a real 2d matrix. I am taking its fft using fftw. But the result of using a real to complex fft is different from a complex ( with imaginary part equal to ...
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2answers
98 views

FFT frequency is always half of expected

I think I have a bug in my understanding of the complex FFT and it's leading me to get half of my expected frequency. I'm trying to calculate the frequency of an input signal of known frequency ...
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1answer
45 views

fftw log-log plot

I am taking Real time fft of an Audio Signal using fftw library. I take the output of the fftw signal on y-axis and plot it against the linear frequency bins on x-axis. I 've noticed that Spectrum ...
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37 views

How to calculate the frequency shift of FMCW transmitted signal and received signal using Matlab?

I generate a FMCW chirp signal between 18k-20kHz using Matlab, then sound the signal through the speaker in laptop, then record the reflected signal through the Mic in the laptop. What I want to do is ...
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19 views

Representing and compartmentalizing FFT of audio sample into user friendly spectrum (need direction)

I am using the Apple accelerate framework to do some audio FFT analysis. Here is what I have so far and I want to make sure that my methodology is correct and I am indeed displaying appropriate data ...
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1answer
28 views

zero-phasing frequency components while keeping the same magnitude, in Matlab

How is it possible? I was thinking of taking just the real part of the DFT of my signal (isn't that zeroing out phases?) with real(fft(X)) but the magnitudes ...
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1answer
105 views

Why do we discard imaginary part of the phase spectrum?

Suppose I compute phase spectrum from the fftn function in MATLAB as ...
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4answers
168 views

Fastest implementation of fft in C++?

I have a MATLAB program that uses fft and ifft a lot. Now I want to translate it to C++ for production. I used OpenCV but I ...
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1answer
32 views

I want to calculate the period of the discrete time sequence from taking its fft(x,N). Can any one help?

This is my discrete time periodic signal, the time resolution of the samples is 0.2ms. And it's periodic after each 11 samples. So the fundamental period of the signal is 2ms or the fundamental ...
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3answers
68 views

EQ - Calculate the power per Octave of a signal through FFT

I'm working on a audio Equalizer, and I'm not sure if the way I obtain the power per octave of my signal is good. Here is the code I have : (I use the third octave bands, which is initialized earlier ...
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1answer
64 views

IFFT Synthesis from an empty spectrum

I'm trying to generate a sawtooth wave using the IFFT. I can do this successfully by first performing an FFT and then putting that analysed spectrum into the IFFT, however I would really like to be ...
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23 views

Getting better results from the Lomb Periodogram of a time series

Two times series were simulated, one with a period of 100 and the other with periods of 20, 40, and 60, for example: ...
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2answers
32 views

phase, magnitude, audio file and information

I've been doing some thinking lately. I know that for image files a larger portion of information is contained in the phase of the signal. How does that go for the audio? Does the same hold or is the ...
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1answer
55 views

Cross-Correlation to find the similartity of songs

I have been working on a problem where I am given two songs which are of the same category but there is a time difference between them. Eg. one song starts at x sec and other song starts at y sec. So ...
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37 views

Doubt related to application of FFT

I found this formula in a paper : http://ieeexplore.ieee.org/xpl/articleDetails.jsp?reload=true&arnumber=5655742 could someone explain the meaning of "j is frequency sample in the highlighted ...
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24 views

FFT analysis for series of different length

i have some data series in time domain which are in different length. i'm using FFT to transform them to frequency domain and now i want to calculate their average. Since their lengths are not equal ...
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3answers
144 views

How condition for existence of Fourier transform is valid?

The condition for Discrete time Fourier transform to exist for function $f(n)$ is given as $$\sum_{-\infty}^\infty |f(n)| < \infty.$$ In case of continuous Fourier transform the difference is ...
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1answer
54 views

How to find phase shift and process I/Q channel

I am currently working of 24GHz FMCW radar signal processing. The Module I'm using has 2 receiving antennas and each has 2 outputs (I and Q channel). So overall I've 4 channels. I'm using combination ...
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33 views

how to estimate the PSD using yule walker method in C++

I'm trying to estimate the PSD (in Yule-Walker method) from the FFT output in C++. First I convert the discrete signal in time domain to frequency domain using FFT. The FFT output contain the real ...