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

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How to Actually Use FFT to implement Low Pass Filter

have searched high and low for a practical guide to implement a simple 50Hz low pass filter on a signal.I understand the theory but its the practical but that's missing. If I was using MATLAB it would ...
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10 views

Zero Centering Audio for Forward FFT

I'm trying to work out the best way to zero centre an audio clip for a forward FFT. I've been trying rotate my audio so that a peak exists mid way (N/2). This seam a little naive and I thought I ...
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1answer
36 views

Averaging different frequencies

How does one average a group of frequencies? Frequencies taken for example using FFT. That is, given n frequencies over m time intervals (n $\leq$ m), how should one "interpolate" between those ...
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50 views

Seamless audio loops via Fourier transforms?

I am trying to create short seamless loops of continuous sound. I recorded myself making an "Aaaaah" sound at 44.1 KHz, and cut this recording to a section containing 4096 samples (giving me slightly ...
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69 views

correct way for Zero padding

I am doing simulation of FMCW radar. I am applying signal processing chain on raw radar data. Here in the code below, I am taking fft of data and plotting it. ...
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47 views

Real world dsp implementations examples?

Well,this may be basic, but i find you as the best option to answer this. I am electrical engineer and i have taken dsp courses. There is some algorithm that i am trying to implement on audio signal ...
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3answers
73 views

Extreme audio stretching

This tool (Paul's Extreme Sound Stretch) is able to produce extreme timestrech (50x, or even 100000x). Any song can become an interesting sound texture or ambient music (listen to this example). The ...
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1answer
51 views

Conversion of FFT to PSD

I would like to convert FFT data which is set of 396 values for 396 frequencies (from 4Hz to 399Hz by 1Hz) in unit of g's (gravitational akcceleration) to PSD in unit of (g^2)/Hz, is it possible? ...
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1answer
34 views

Pitch Detection / Harmonic Product Spectrum - What's wrong?

I've whipped together a small example that tries to use the Harmonic Product Spectrum Algorithm to extract the pitch of a simple sine wave. I'm not sure about my implementation and if i understood ...
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0answers
43 views

Subtracting one FFT from another for noise reduction

I am using an FFT/iFFT library in c#, and working with arrays of audio & complex data. What I am hoping to do is take a small amount of 'background' audio signal, and use it as a fingerprint to ...
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1answer
14 views

What is the minimum number of time points recommended for accurate instantaneous phase estimates using the Hilbert transform

I have two time series. The two series look like they follow the same function, but one appears to lag slightly behind the other. I would like to determine if there are phase differences between the ...
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2answers
37 views

How to calculate resolution of radar

I am working of FMCW radar. Below are all the parameters of FMCW radar. How can I Calculate the resolution of my radar ...
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0answers
22 views

Is it possible to compute the magnitude of a length 2N DFT of a real signal with the magnitude output an N-point FFT?

I know it's possible to get the length 2N DFT of a real signal with an N-point FFT like so (page 2). My question is, can I do something similar with magnitudes only? That is, take the magnitude of the ...
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19 views

sound FFT data to PCM data

I have some FFT data, 257 dimensions, every 10 ms, with 121 frames, i.e. 1.21 secs. I think the first dimension is probably something else and the remaining are the FFT coefficients, I guess. From ...
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1answer
33 views

Can you simulate the “response time” of a lower window size FFT on a higher window size?

Can you simulate the "response time" of a lower window size FFT on a higher window size? That is, is it possible to calculate the equivalent lower window sized FFTs from a higher one in order to ...
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1answer
45 views

Per Window Normalization

I have PPG signal that should be normalized, with offline processing I'd just do $z$-normalization, $$ \displaystyle \frac{x- \mu_x}{\sigma_x} \quad \text{where } x \text{ is the signal.} $$ The ...
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0answers
19 views

Does OS method for calculating FFT offer any better frequency resolution than normal?

Do we have any advantages of using Overlap Save method while calculating FFT ? Does it increase the frequency resolution ? Also which is beneficial : padding zeroes or extracting a block of samples ...
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0answers
70 views

Difference between summation of motion components and IFFT?

I have a problem using the IFFT command. I want to see if i can go from the frequency domain to the time domain of a signal. I wanted to test this in two parts: 1) first creating a wave time ...
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1answer
10 views

How to analyse periodic data obtained from a vibration experiment?

I have data from a vibration experiment on a structure. This data was obtained by attaching an accelerometer to a FFT analyser, which records the data at a high sampling rate (typically in kHz range) ...
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2answers
51 views

how to match 2 signals that have same information, though shifted and scaled

I have 2 signals S1 and S2 that contain the same information, but S2 is shifted and scaled compared to S1 by an unknown amount (but small; eg shift would be of the order of 1-10 samples). What is the ...
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0answers
12 views

How to take IFFT of Connes Window?

The Connes Window function is defined as : w(f)=$(1-(\frac{f}{ \Delta f})^2)^2$ for $f<|\Delta f| $ w(f)=0 otherwise The inverse fourier transform of this function can be ...
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2answers
27 views

sinc interpolation using fft

Lets say I want to double the number of points in an array f. I had the idea to do this: F=fft(f);N=length(f); FF=[F(1:N/2) zeros(1,N) F(N/2+1:N)]; f=ifft(FF); ...
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18 views

Time domain sweep function to frequency domain

I have an input sweep sinusoidal signal (constant magnitude sweeping the frequency range of 0.1 to 25 Hz) to my mechanical system. My question is that to analyze the output signal as an acceleration ...
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49 views

How to resample a continuous stream of data

I've been working on a project that requires resampling a continuous stream of data. It will eventually be implemented in C/C++, but for the time being, I've been conceptually designing the process. ...
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1answer
75 views

Python - time frequency spectrogram

I have some 64 channel EEG data sampled at 256Hz and I'm trying to conduct a time frequency analysis for each channel and plot a spectrogram. The data is stored in a numpy 3d array, where one of the ...
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38 views

How to look at 2KHz to 2.5KHz with a 1024 FFT

I've tried searching for an answer to this, but i don't think i'm looking for the right thing. Lets say i wanted to examine a signal in the frequency domain that's between 2K-2.5KHz. Can i do this ...
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1answer
21 views

Exact indices of fft

Lets consider the cyclic frequency transform and lets try to make it so that the transform of the function is itself. ...
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54 views

Beginner question on aperiodic samples and DFT behavior

I have a strongly aperiodic signal and I get weird artifacts after running a fft, using a low-pass filter, and then doing an inverse fft. I believe the artifacts are due to the way the signal is ...
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1answer
46 views

How to Flip Spectrum Around DC?

Is it possible to flip a signal's spectrum around DC? I have a simple spectrum that I made up (MATLAB code): ...
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1answer
55 views

How to Combine FFT Overlap Results?

We currently have C/C++ FFT code with Hann Window function support. For a large data (over 10,000) we want to split this into 1024 samples with 50% overlap. For each 1024 sample, we window and fft. ...
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2answers
60 views

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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3answers
49 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
46 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
31 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
51 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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19 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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2answers
38 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 ...
0
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1answer
43 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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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
46 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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2answers
54 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
57 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
64 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
174 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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27 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
52 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
35 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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30 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? ...
2
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1answer
101 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
73 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 ...