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

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9 views

How to calibrate two microphones to same frequency range

I am recording stereo with two same microphones but they are physically insulated from eachother and have some additions on sound input side. Not to complicate story, I have a human head simulation ...
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2answers
22 views

Measuring amplitude of a spectral component

I'm trying to measure the amplitude of a spectral component in a signal. The component's frequency is always known beforehand. I take a given number of samples, apply the flattop window to reduce ...
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1answer
11 views

Explain how to apply Hanning window to Fourier amplitude spectrum

This example code was used to answer a question about applying a window on the Fourier amplitude spectrum. How to apply Hamming Window? I have a question about the section of code related to the ...
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2answers
23 views

Sampling rate vs sampling time of FFT

I am having some trouble understanding the sampling time and frequency used in the computing of the FFT, and I was wondering if someone could make it clear for me : The Sampling time: the time in ...
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0answers
11 views

Noise removal of an audio signal (.wav) using matlab [on hold]

I was given an audio file containing noise. It's required to find the noise frequency components and then remove them. Finally play the noise free audio signal. Here's what I did so far: ...
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1answer
56 views

Obtaining the FFT of a data set collected through an accelerometer

I'm using MATLAB to analyse a very large sample of acceleration data collected using the MPU9150 IC. My aim is to plot the FFT for this large sample of data. The daya is of three axes; $x,y,z$ and I ...
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1answer
40 views

Difference between fft(signal, nfft) and fft(signal)

I want to know the difference between these following commands (matlab) and why I get two different outputs? fft(signal); fft(signal, nfft); I found that ...
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1answer
43 views

DC component in accelerometer data - filter before or after XYZ Euclidean sum

I'm working on filtering accelerometer XYZ data. The aim is gait-pattern recognition via finding characteristic frequency points and feeding these to a artificial neural network. The trouble is, and ...
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1answer
49 views

Features of a non-periodic signal for comparison

I am looking for comparing a signal (256 / 512 point discrete | non-periodic ) (obtained after extracting some features from the captured image) with a database of around 5000 signals (256 /512 point ...
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1answer
26 views

Do I need the sampling frequency in order to gain periods out of FFT?

Currently I am using the transformInPlace() method from here. for a project at university. First of all I thought FFT would be the perfect solution for my ...
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0answers
16 views

Plotting band-pass filtered signal of an audio in MATLAB [closed]

I am new in MATLAB and try to plot some form of an audio file and I have managed to open and plot in time domain and FFT using the following code: Step I: Opening the Wave File ...
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0answers
17 views

How to get real fft from complex fft calculation using butterfly Decimation in Time approach? [duplicate]

I have written a code to calculate fft using a butterfly structure algorithm. The input to the fft are sampled values of single frequency sinusoidal wave. I need to find real fft, using complex fft ...
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1answer
44 views

How many DFT bins must I use to get best precision when analyzing melody scale

I need to analyze some signals containing chords. How big DFT spectrum is needed to identify each possible musical note in such a signal sampled at 44100 Hz? I can see that 8192 bins gives some ...
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1answer
30 views

Where does $\frac{N}{2}$ came from in approximating an N-point DFT?

I've came across the author saying that ... for a real cosine input having k cycles in the N-point input time sequence, the amplitude response of an N-point DFT bin in terms of the bin index m is ...
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0answers
17 views

How to generate values for frequency axis (y-axis is fft of a signal)? [duplicate]

Suppose I have a signal as a function of time: x(t). If I call fft(x(t)), I will get the spectrum of ...
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0answers
46 views

How to shift a signal to the center of the frequency domain?

Let's assume I have a 1024 x 1024 matrix that represents the spatial domain. After I perform a FFT and center the frequencies, I get the a signal that looks like the following in the frequency ...
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1answer
39 views

FFT: Linear to Logarithmic (TM4C, CMSIS & NeoPixels/ws2812)

I'm trying to perform an FFT using the CMSIS libraries. My FFT_Output[] provides 1024 bins of data as expected. The issue is that it's linearly spaced and I want to change it to a logarithmic scale ...
-2
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0answers
23 views

FFT performed, extract sample? [duplicate]

so i have 250,000 data points and i have applied an FFT and received 250,000 Real and imaginary numbers. I now want to graph it up to a frequency of 250Hz. Does that mean my bin size is 1? i.e. data ...
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2answers
62 views

Two-Sided Frequency Spectrum

I am trying to make FFT simulation in Matlab by generating noise added two sinus waves in 60Hz and 100Hz. After adding the noise into these signals then I have applied the FFT as I put my Matlab code ...
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0answers
18 views

Is adding zeros part of the Hermitian Symmetry process?

I have been reading about DMT/OFDM and every source I find defines their system differently. I simply want to know if zero insertion is part of the Hermitian symmetry process that produces real OFDM ...
3
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1answer
67 views

FFT of a $N$-length real sequence via FFT of a $N/2$-length complex sequence

I am doing FFT. The one way I did is to put real part in one array and the imaginary part as zeros and then calculated the FFT. But this take up lots of resources. Now I want to calculate FFT by ...
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2answers
46 views

Is this graph of Wigner-Ville distribution OK?

I am studying some code for smoothed Wigner-Ville distribution. update 3- solution, graph was over amplified in a 2d overdrive/oversaturation effect. if i divide by 20 only a line is visible. Update ...
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2answers
24 views

Combining channels into single FFT left/right vs mid/side

I am creating a spectrum analyser to visualize some stereo audio data in real time. I want to display a single spectrum for the input and a single spectrum for the output. The stereo data is the usual ...
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2answers
42 views

How to do the highest resolution FFT?

I wish to do the FFT of streaming audio data coming into a computer. I am just interested in frequencies from 80 Hz up to 1000 Hz but with a frequency resolution of 3 to 4 Hz and no more. Basically ...
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0answers
45 views

How to separate opposite direction travelling waves without artefacts?

In shear-waves ultrasound imaging, waves are created which travel in opposite directions. there is need to extract left going and right going shear waves. I have used wavenumber-frequency domain to ...
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1answer
40 views

Why is this FFT code not working to extract frequencies from a wav audio?

I'm quite new to audio processing and i'm trying to extract frequencies from a wav file. As research papers stated i put the wav audio into a byte array and segmented and trying to apply FFT to get ...
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1answer
30 views

FFT plot in GNU Radio

i got similar question as in FFT scaling in GNU Radio and quite not clear about the answer given so far. I understood that the FFT plot is a relative value in which we have to use measurement ...
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3answers
61 views

Performing DFT of streaming audio problem. Is there a limit?

I am trying to write software that will perform the discrete fourier transform of real time data coming from the microphone into the sound card on a computer. I am using Java with the javax.sound ...
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1answer
34 views

Possible to shift image pixel-wise with FFT?

I know we can shift an image entirely with FFT as http://stackoverflow.com/questions/25827916/matlab-shifting-an-image-using-fft However, is it possible to shift the image pixel-wise? I just found a ...
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2answers
42 views

Aquila DSP C++ Library - Wave file FFT analog frequency off by factor of 4?

I'm working with the Aquila C++ DSP library. I'm computing the FFT of a wave file (16 bit depth, single channel, 44100 sample rate). I am using a window size of 16384 to calculate the FFT spectrum. ...
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2answers
57 views

Play IQ data in the soundcard

I have short-wave digital receiver that send RP packets with IQ components over network depend of the RF frequency and passband. I need to work with the telephone passband (0.3 - 3.4 kHz). The task ...
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1answer
55 views

Getting frequencies out of a FFT

I use this FFT and wrote a short program to test it. ...
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0answers
21 views

Image Rotation using 3 Shears, Implemented using FFT-based Shifts

So I'm trying to rotate an image using the 3-pass shear. We're implementing the 3 shears in Fourier space, so we're taking the the rowise/colwise FFT, then multiplying it with e^ikx, with necessary ...
3
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1answer
70 views

Reduce the number of frequencies after FFT

I have a long signal (1 day sampled at 500 Hz), which results in many frequencies if I calculate the amplitude spectrum (see e.g. here). However, I am only interested in the "big picture", let's say ...
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0answers
22 views

Calculating Time Delay between initial sound and its reflection [duplicate]

I have been researching into calculating distance using sound on an iphone 6. I have been playing short frequency sweeps on one iphone and recording the data on another phone sitting on top of the ...
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2answers
40 views

Reduce “flicker” in spectrum analysis / spectrogram

I'm performing a series of FFTs on windowed extracts of an input signal, to get a frequency spectrum over time. This is for a visualisation - I'd like to keep the window small, so the visualisation ...
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1answer
26 views

FFT Resolution Inference

Let's say I have an audio clip of $N$ samples. I want to describe every $10$ ms of audio with an FFT of size $1024$, without information bleeding over from other $10$ ms windows. Given that the ...
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0answers
35 views

Are wavelets for audio spectrograms available as a simple FIR filter?

I have read that "Debauchies Wavelet is simply a short FIR" so i am searching for a single FIR that i can make into a filterbank, a precise "bandpass filter" that detects narrow frequencies, i.e. 1Hz ...
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0answers
44 views

Fourier transform on Scilab of a Gaussian function

I am trying to do a fourier transform on Scilab, of the Gaussian function $y(x)=\exp(-\frac{x²}{2})$, by using the fft command. So I plotted the graph of ...
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0answers
25 views

Obtaining a frequency response from other frequency responses

I have loaded six impulses responses (1024 samples each in length) into Matlab, zero-padded the end of each with 1024 zeroes and taken 2048 point DFTs of each using Matlab’s built in ...
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3answers
78 views

Convolution and windowing using a buffer - how do I do overlap add?

I'm reading chunks of audio signal (1024 samples) using a buffer, applying a Hanning window, doing an FFT on it, then reading an Impulse Response, doing its FFT and then multiplying the two ...
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0answers
27 views

Total Harmonic Distortion + Noise calculation

I'd like to display calculated power line THD+N on a Smart Meter application. Is there a common algorithm or procedure to get it? I think I could manage to sample data up to the 5th harmonic and then ...
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2answers
54 views

FFT output to graph

I have a hydrophone which gives input into my PC as voltage. I have an FFT which uses both real and complex numbers; however the hydrophone output I have set as the real and have set complex to all ...
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1answer
30 views

FFT and input voltage

I have a hydrophone which sends voltage as input into my PC. I want to pass this through an FFT, yet from what i can find real and imaginary numbers are given as input. How will this work for me? Or ...
0
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1answer
28 views

How to measure noise, consonance, dissonance of a sound?

How can I make a graph of the noisiness of some audio durations of 100ms - 10s with 100% being white noise and 0% being a sine wave. I have FFT at the moment, are there other ways to know the ...
0
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1answer
71 views

Why does this reconstruction produce a phase shift from the original signal?

After an FFT of a signal is done, it is plotted as in the image below, with the original signal is on the first subplot. Using the magnitude and phase data of each frequency, it's reconstructed, ...
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1answer
56 views

1D FFT algorithm elements explanation?

Can someone explain to me what each element of the 1D FFT algorithm are (i.e. N,x,n,j,k) ? From here, http://zone.ni.com/reference/en-XX/help/371361H-01/lvanls/fft/#details (Can't post pictures on ...
2
votes
2answers
109 views

Extracting accurate phase and amplitude information from FFT with an arbitrary number of samples

This is a followup question to one I asked earlier based on the chat after the answer given by @hotpaw2, and cross-posted from stackoverflow since it was suggested it is more relevant to DSP. I have a ...
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2answers
65 views

Get position of different frequencies in sound signal

Assumed I have a signal where different frequencies appear depending on the time position, i.e. a signal of $440\,\textrm{Hz}$ appears at $t=0$, a signal of $441\,\textrm{Hz}$ appears at $t=1$, a ...
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0answers
59 views

How to convert fft plot into PSD(Normalized) vs Freqeuncy (Hz)

I am trying to convert my fft signal into PSD(Normalized) vs Freqeuncy (Hz) but can't get it right. I want to get some thing like shown in the figure. I found these figures in the literature. How to ...