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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What is the computional complexity of the Burg method, zero crossing and pspectrum?

I am trying to get information about the computational complexity of the Burg Method, pspectrum and the zero-crossing. I already tried to search that information by google, but couldn't find anything. ...
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Interpreting FFT Phase - why phase of a cosine?

I understand how to interpret the magnitude result from the FFT, but why is the phase that we obtain, arctan(Im(x)/Re(x)) indicative of the phase shift of a cosine graph, and not a sine graph?
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how to choose the right FFT Length for a defined Signal

I want to use FFT in Simulink for : The useful signal has a frequency of 10 Hz and Uspitzespite is 5 V The excitation signal has a frequency of 10 kHz and peak-to-peak is 0.5 V. The data from the ...
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24 views

How to determine number of filters in filter bank based on spectrogram of audio signal?

I want to do an analysis and than synthesis of audio signal, which is audio of vowel 'a', using Matlab. For this I need to use filter bank(array of band-pass filters). I have drawn four different ...
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43 views

Separation of sinusoidal oscillations from the frequency spectrum

It is necessary to extract the harmonic signal from the audio spectrum. That is, from the spectrum of 20 ... 20,000 Hz it is necessary to select only a signal with a frequency of 1,000 Hz, and ...
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Unknown reason why the frequency spectrum of a “knocking force” (impulse) gets some spike

During my experiment (vibration analysis), I deliver a knocking force from a shaker (and the shaker itself has an impulse or an half-sine wave signal). The system automatically calculates with the FFT ...
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27 views

FFT calculation of an N-tap FIR filter

I have the following question: a) For an N-tap FIR filter, sketch the direct form realization. How many multipliers per sample? You may choose 8. b) For an FFT calculation of an N-tap filter sketch ...
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215 views

Problems computing the DFT of finite length sequence

I am having trouble finding the same answer as the solution manual for this sequence. The problem asks to compute the DFT of $$ x[n] = \begin{cases} 1 & \text{for even } n \in \{0\...
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Should we divide the power at 0Hz by two for Single-Sided Power Spectrum with FFT?

To make my question as clear as possible I will go through an example. I want to plot one sided power spectrum of a signal. As an example my signal is sum of "50Hz sine with and amplitude of 1V&...
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38 views

Meaning of the frequencies vector using fft

I'm so confused, and it would be nice if someone could clear my head, or at least direct me to suitable references. Assume that I have two gaussian pulses with the same bandwidth in time, but for 2 ...
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56 views

Why do the DTFT and FFT give me completely different results for magnitude at a specific frequency?

I am trying to write a program to compute the magnitude and phase of a specific, non-integer frequency component (i.e. given a sampled finite signal of length $N$, I want to know the magnitude and ...
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The best method to convert piano sound to music notes in real time [duplicate]

I was looking for a way to convert piano sounds to piano notes for my research. I discovered the conversion of piano sound to piano notes using FFT and piano note recognition using CQT. I am also a ...
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Possibilities in Audio Convolution Math

New Python user here! I am a musician working on a program to streamline a process of using convolution math on a folder of .wav samples. The idea is that each audio sample will be multiplied with ...
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The effect of time increment $\Delta t$, frequency resolution $\Delta f$ and Gibbs phenomenon on the amplitude of the signal in the frequency domain?

Experiment: Vibration analysis (i.e.: major concern is on transfer function or frequency response). The input is an impulse (imagine as a knocking effect or knocking force), defined as a half sine ...
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In the context of DFT, Where Does the Nyquist Frequency Sample Belong In a Double Sided Frequency Spectrum (Positive / Negative Side)?

If we have an even number of data points $N$, after DFT in MATLAB, the output has the order: $$(\text{DC}, f_1, f_2, \ldots, f_{N/2-1}, f_\text{Nyq}, -f_{N/2-1}, -f_{N/2-2}, \ldots, -f_1)$$ For real ...
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I need help interpreting FFT diagram

I need help with analyzing the computed FFT of my signal. I don't wanna bother by going into the details of how my signal is formed so I will just state which frequencies I know my signal has. I know ...
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Properly stagger an FFT? How to handle output data (Have highs weigh as much as lows?)

I'm new to audio processing so I'm mostly running into problems with not being able to properly google something. Sorry. Basically I want to create something like an equalizer (just visually without ...
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51 views

The effects of frequency resolution in FFT on the frequency spectrum

This is a section for the parameter study of my thesis (basically: why and how I did what I did in the experiments). Currently, I have to choose the fit bandwidth and FFT lines combination for the ...
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Calculate periodicity of audio signal

I have to calculate the periodicity of a audio signal like this: You can see by eye, that the volume rises the highest every second "blob". The spectogram (that is visualized ...
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76 views

Difference between $\tt fft$ and $\tt dftmtx$ in MATLAB

I have the following MATLAB code: ...
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1answer
77 views

Frequency from mic Raspberry Pi

I am working on C++ project based on Raspberry Pi. I have to make program that recognize siren of emergency vehicle(sound capture by microphone). I made a huge internet research and stopped with small ...
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94 views

Non-zero DFT components where zero is expected?

I am implementing DFT in Octave. Here's my code: ...
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1answer
36 views

Where 2-D DFT is necessary in image processing applications instead of 2-D DCT?

As we know the 2-D DCT is a real-valued kernel and less computational complexity and it used in several image processing applications like image compression etc. 2-D DFT is a complex kernel and high ...
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3D data centering before fast fourier transform

I am using fftw to conduct a 3 dimensional fft and then apply a guassian filter. In order to shift the frequency, I need to first rotate the data matrix before fft. In 2D, I know how to do it, e.g., ...
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296 views

(I)FFT without Bit Reversal

It's been a long time since I scratch built an FFT algorithm, and I feel like I should already know this, but I just can't recall and figured I might get a quick answer on here that may be useful to ...
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Why the inverse discrete fourier transform of the Ricker pulse isn't the same as the Ricker pulse in time domain?

Question I'm trying to use Python's scipy library to compute the IDFT of the Ricker wavelet function and compare it with the analytical time-domain version of the same function. When I compare the ...
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51 views

Do i need to remove mean in STFT when working on music audio?

i need to apply a STFT to some music audio files but i can't understand if i should remove the mean or not. I know that for stochastic signals that is a must and that sometimes also necessary for ...
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How to get the phase/angle from an Alglib complex variable

It is easy to get the magnitude using alglib.abscomplex function (https://radfiz.org.ua/files/temp/Lab1_16/alglib-3.4.0.csharp/csharp/manual.csharp.html#gs_stdfunctions), but I would like to know, how ...
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Comparing two small audio files (e.g., hand clap) Android

Dears, I am new in signal processing and I am dealing with an Android application that should do some audio files (having the same "small" duration) comparison in real time. My main focus is ...
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37 views

Strange behavior from frequency to angular frequency in FFT

I have written a code to compute the Fast Fourier Transform of a simple complex exponential with frequency $f=50.0$, using scipy.fft. The code is written below: ...
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83 views

Inaccurate phase returned by np.angle

I am generating 2 sine waves, first one has fundamental frequency = 50 Hz, amplitude=10, phase=0, the second one has fundamental frequency = 100 Hz, amplitude = 5 and phase = np.pi/6 (which is ...
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How to conduct spectrum analysis on a wav audio file using SciLab?

I am working on a wav audio file using SciLab. The wav file is to undergo the FFT (Fast Fourier Transform) by using the fft function to obtain the spectrum analysis ...
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Forecasting that FFT result

I have the following FFT result charts. Searching for a way to forecast the future AMPLITUDE steps from the Time Domain Plot if possible, or the next maximum/minimum deviation based on some previous ...
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1answer
23 views

Convolution output signal is very large, do I need to scale inputs or outputs?

I am writing some simple matlab code to refresh my convolution knowledge (it has been awhile) in regards to DSP. I have an input signal x and a filter - ...
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40 views

FFT on a Raspberry Pi

I'm trying to determine the processing time required to perform a FFT of length 500,000 on a Raspberry Pi in C/C++. I have had difficulty finding any information that would be useful for determining ...
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1answer
117 views

Circular Convolution and FFT of power 2

I am currently trying to understand the Chirp Z Transform, and compute an FFT for a vector that has size which is not necessarily a power of 2. The key step in the Chirp Z transform to recognize that ...
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Generating a time domain signal using the fundamental frequencies

I currently have the power spectrum (in dB) of a signal through which I obtained the fundamental frequencies and amplitudes. My question is: how to generate a time domain signal using these amplitudes ...
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Trade-off in sample-rate & FFT-size & Doppler

I've got a stream of digital IQ samples let's say at $F_s = 1 MSPS$ that consist of a narrowband signal, in awgn. Let's say the signal BW is ~ 100Hz. The narrowband signal's center (or base) frequency ...
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55 views

If a time-series has odd number of samples does it have no energy at Nyquist frequency?

Suppose I have real time series A with n samples and time-spacing dt and I want to analyze ...
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1answer
34 views

Estimating a phase for a frequency band

I'm looking for a way (preferably already implemented in eg. python) of estimating a phase for a specified freq band. When I'm performing FFT on the signal, I can determine components frequencies as ...
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1answer
27 views

Swift vDSP rFFT not same as Python np.fft.rfft()

I am trying to implement real FFT in iOS, for that i am using Accelerate Framework. Here is my Code for Swift. ...
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What could cause a phase difference between a FPGA implemented FFT and numpy.fft.rfft

We have a FPGA system which takes input from an ADC and calculates a FFT. The system identifies the location of our frequencies of interest and sends the coefficients from those bins to my software. ...
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What's the ideal FFT window for measuring a group of signals of differing amplitudes but close in frequency?

In my system, I need to measure the amplitudes and phases of four lasers, each of a different, known wavelength, chopped at a 50% duty cycle via TTL at frequencies spaced evenly (or not) around some ...
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How can I do a validity check of an FFT

The aim is to identify problems in an ADC FFT simulation in an early phase of the simulation using the output bitstream of the ADC. The reason is to avoid long simulation times while using wrong data. ...
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1answer
55 views

What is the difference between the spectra of white Gaussian noise and of a Dirac impulse?

Perhaps it is a basic question, but can anyone explain the difference between the spectra (or power spectral density) of white Gaussian noise and a Dirac delta? They are both constant over the whole ...
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How to successfully resolve multiple pulsation frequencies in the FFT?

I am dealing with signals that in both extreme cases can have: a) Non-overlapping monochromatic pulsation-like events at different points within a time series. b) Overlapping pulsations at multiple ...
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Meaning of lines on x- and y-axis of a centered FFT-spectrum of an image

I am currently learning about the Fourier transform of digital images, but I am wondering about one aspect. In most visualisations of fourier transforms of images, a horizontal and a vertical line in ...
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66 views

Difference in information between IQ Sampling vs. Real Sampling at $2F_s$

As per my current understanding we use IQ sampling as way to increase the useful bandwidth to Fs rather than $F_s/2$ when viewing the FFT because the IQ sampling removes the negative frequencies and ...
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Plot Spectrogram and FFT plots from samples collected by Atheros AR9271

I'm entering the world of signal processing, and as one of my first projects I've decided to plot a spectrogram and FFT Plot. The samples comes from an Atheros AR9271. More details can be found here: ...
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211 views

Interpreting N in DFT as the Number of Points vs. Number of Intervals

The "N" is DFT is understood to be the number of data points in a given sequence or in other words the length of the sequence. We recently have had discussions here Indexing in DFT (from an ...

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