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

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Gaussian wavelet generation of a given frequency

How can I generate a Gaussian wavelet (time domain) with a given central frequency. I mean, if I take the Fourier Transform then its spectrum should be around that given central frequency. For ...
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32 views

Hilbert Transform from FFT?

For a school project, I'm working on a software-defined radio transmitter intended for the HF amateur radio bands. I'm planning to support SSB transmission with the formula $$f(t) = m(t) \cos(2\pi ...
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How to realize DFT6 with 3 DFT2 blocks?

Is it possible to realize DFT of 6 samples by using 3 DFT2 blocks? For example if had 2 * N samples by one step of decimation in frequency or time is possible to reduce DFT(2N) to 2 * DFT(N). So if we ...
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1answer
21 views

GQRX Frequency tuning

In GQRX (an GNURadio based RTL-SDR receiver) I have an FFT and waterfall display. When I tune to a local FM station (107.5MHz) I can hear strong, clear voice. But on FFT and waterfall display I can ...
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50 views

Converting magnitude to dBs

I have seen people using 10*log10 and/or 20*log10 while converting magnitude to dBs. What are the differences and which one is valid?
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46 views

FSK Demodulation in Python

I'm trying to demodulate an FSK audio file. The data are from geospatially encoded media where NMEA GPS strings were encoded to audio with 4800 baud and embedded in video. My goal is to use Python to ...
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23 views

How to calculate output from non-uniformly sampled transfer function data?

I have non-uniformly sampled transfer function data (magnitude only) in the range of 100kHz and 200MHz. Using this transfer function, I would like to calculate output from specific input. Question : ...
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10 views

Autoregressive Model for EEG frequency analysis?

I want to do EEG frequency analysis in matlab using autoregressive models (e.g. Burg's method). How do I do this correctly? I just treated each channel individually (loop over channels), so I go ...
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1answer
41 views

removal of blackman harris window results in signal higher than expected

We are capturing data using a PX14400 adc. The samples are 16bit unsigned integer, 200M samples/sec, I data only. 100MHz bandwith. We have a cw signal at 51MHz, -11.4dBm. The -11.4dBm is measured ...
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1answer
25 views

normalize fft produced by fftw_plan_dft_r2c_1d

fftw_plan_dft_r2c_1d takes an array for real numbers and produces an array of complex numbers 1/2 the size of input array + 1. per fftw's website: As a result ...
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3answers
32 views

Extrapolation after taking inverse Fourier transform

Suppose I have 2000 point(time series) signal and I take 512 point FFT, after this some operation is done in frequency domain. Now if I take IFFT to get 512 points in time domain, Is there a way to ...
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21 views

How to calculate energy of an OFDM signal?

What is the difference between power and energy of OFDM signal. How to calculate energy of an OFDM signal, if we consider OFDM symbol size is 64, and QPSK is used as modulation scheme?
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Filtering noise from FFT, where noise is known to be shifted delta function

I have an input sequence $x=\{x_1, x_2 , ... x_n\}$ of reals, where $n=2^m$ for some $m$. I wish to calculate FFT of $x$. $X=FFT(x)$ However, before I calculate the FFT, the signal $x$ gets ...
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0answers
40 views

FFT and Power Spectrum from Time series using MATLAB

I'm trying to better understand some things about FFT so I've asked for a small assignment, in MATLAB, in which I'll make some signal analysis on existing data. All I have is a time series which is a ...
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1answer
30 views

Why do I have to divide by $\pi$ in order to scale amplitude of sine frequency spectrum?

Recently I found my old code to transform sine wave from time domain to frequency domain. Below I post simplified version of it. ...
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2answers
51 views

Finding a signals complimentary sound / frequency

I know about complimentary colors and how to get them, since colors are basically frequency / wavelengths. Is it possible to find a signals complimentary, additive or subtractive frequencies in an ...
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0answers
27 views

Regarding maximizing signal to noise ratio

If I have 3 recordings, each of speech (recorded in a relatively silent room), speech+background noise and background noise then is there a way to utilise the data from all the three to extract clear ...
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2answers
23 views

How much can the FFT noise affect the timbre analysis of a harmonic sound?

The timbre of an harmonic sound (e.g. the steady part of a violin note) is defined by the amplitude of each harmonic (including the fundamental). In order to compare the timbre of two instruments ...
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1answer
32 views

STFT Window Size is 2048, Why is the output 1025?

I feel like I am having a brainfart over here and can't seem to remember what's going on with STFT outputs. Consider these two lines of code from the Python library Librosa: ...
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2answers
97 views

FFT of SIN waves with different phase delays

I have come across a peculiarity of FFTs which has got me somewhat baffled. I've simply summed up 101 sine waves and taken the FFT using this matlab script : ...
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1answer
64 views

DFT Filter Banks

i have a doubt about DFT filter banks. For example I have $M=4$ channels and a filter with cut-off frequency of $0.25$ right. The prototype filter $H_0$ is a low-pass centered around $0$ ok. The ...
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1answer
63 views

Optimized 2D wavelet transform using FFT

I'm currenty aiming to optimize my fast wavelet transform (FWT) algorithm for 2D signals (images). It works as follows: one iteration of 1D FWT does convolution of 1D input data with a selected 1D ...
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2answers
76 views

FFT, padding, IFFT and plot in time domain

I performed an FFT with some zero padding and would like to transform it back to time domain. When I plot the signal it looks wrong. Is it because of the padding used in the FFT? How can I make it ...
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1answer
33 views

Obtaining signal energy modulation for voice activity detection

Im currently working on VAD (voice activity detection) topic. Since I'm beginner in digital signal processing, I've started to wonder if calculating single frame energy (after aplying FFT to it) and ...
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33 views

what does FFT low frequency refer to?

I have applied the fft for image (fluorescence microscope image) and I have got this plot. My question here, what the meaning of that? What and how can I explain this plot?
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75 views

DFT/FFT Transfer function

I want play and record a sine sweep. When i have both signals the recorded one and the send one i can create a Transferfunction. That is what i know so far. $$ H_0 = \frac{OUT}{IN} = \frac{Y}{X} $$ ...
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55 views

finding the fundamental frequency in frequency domain

I want to get the fundamental frequency of a signal. I used a time domain approach first. It just sums up the differences between the signal (lets say 2048 samples) and the delayed version of the same ...
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1answer
37 views

Fixing for windowing function in FFT

I've been learning about the FFT and about the usefulness of windowing functions. A problem I'm running into is the affect of windowing functions on the amplitude of signals in the FFT. For example, ...
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0answers
8 views

matlab spectrum returns more FRAME than expected

I'm using the following code to get specgram2D from np array. ...
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4answers
73 views

Can the FFT representation of a signal be modified w/o creating glitches?

I've read that modifying the bin values in the frequency domain after a FFT poses problems that lead to glitches when one takes the signal back to time domain using iFFT. This is caused iirc because ...
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2answers
49 views

When I ask Matlab for a zero-padded FFT, does it (or FFTW) ever explicitly create a zero-padded input vector?

If I have a length $N$ signal and ask Matlab for an $M$-point FFT, $M \gg N$, of course the computer has to allocate memory for $M$ output samples, but my question is if it ever has to allocate memory ...
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46 views

Different sampling rates causing unexpected results

I am trying to calculate the Modulation Transfer Function of a radio graph. A line is drawn from region of high attenuation to low attenuation and these attenuation values are sampled at the rate of ...
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38 views

Scale of Amplitude in FFT (Matlab)

Using Matlab's FFT function, I am getting different Amplitude values in a particular frequeny, when I use different range of Bandpass filters centering around that particular frequency. What's wrong ...
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68 views

Calculating Beam pattern, Directivity of microphone array

As answered in Relationship of Fourier Transform and Spatial Directivity Pattern the relation between directivity pattern and weights is give. But I am bit confused, I have Beamformer weights ...
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1answer
61 views

FFT Convolution: missing sample somewhere

For a piece of software I've been working on lately I need to implement FFT convolution for performance reasons. Doing so has been mildly succesfull but there is still a error somewhere causing lots ...
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59 views

Accuracy of IFFT(FFT(X)) unit transformation

I want to use FFTs to do seriously accurate interpolation on band-limited data. To do that, I need to get a handle on the fundamental accuracy of the FFT() and IFFT() algorithms available. My idea ...
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1answer
36 views

Fourier transform 4 times = original function (2D and higher)

The Signal Processing SE post linked below shows how the Fourier Transform applied 4 times to a 1D function returns the original function, i.e. F{ F{ F{ F{ g(x) } } } } = g(x) Link to 1D case: ...
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1answer
97 views

Aplying FFT to Wav file data

Technology: C++, CodeBlocks IDE. I've just read sample wav file (source - http://www.wavsource.com/snds_2015-12-13_4694675918641206/movies/2001/daisy.wav ) with an txt output ...
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3answers
422 views

Why is convolution or FFT breaking in this case?

It is well-known that convolution in real space corresponds to multiplication in the reciprocal space. Yet, I obtain different results using both methods in the case that I'm going to present. I am ...
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59 views

Using FFT to demodulated a sine wave envelope with a cosine carrier

I am trying to implement AM demodulation in Matlab by taking advantage of the fact that in the frequency domain, the spectrum of the modulated signal is shifted by the frequency of the carrier. I ...
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63 views

Performed FFT on an audio signal, but what does the output actually mean?

Original post from yesterday here So I did the FFT and I have my transformed data (which is a bunch of values for each frame of data. I'm unsure what the transformed data actually represents. What ...
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1answer
63 views

Performed the Danielson-Lanczos shuffling for FFT, but I don't know what to do next

I'm writing an audio analysis program and need to do some FFT to frames of the data. I've got some code (rather verbose so I'll leave out the details) that successfully performs the shuffling of the ...
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1answer
28 views

Why does this constant-Q transform “lose octaves”?

In this paper (Schörkhuber, Klapuri, Sontacchi), it's shown that the constant Q-transform evaluated "octave-wise" produces the following looking graph: I don't understand why the octaves are ...
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26 views

Sign of DC Component obtained from FFT differs with the sign of Mean of the signal, Does the sign really matter?

I've been working on 3-axis accelerometer data to predict the gesture of an user. Lot of literature pointed me to consider Frequency domain features for my problem and i'm using Mean of the ...
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21 views

Using FFT to determine frequency [duplicate]

I'm pretty new to digital signal processing, my degree touched on it briefly, but it's interested me since. I am trying to determine the fundamental frequency of a guitar note played into a mbed ...
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1answer
50 views

reducing MIPS in detecting tones

Currently our software is detecting tones using FFT and checking if there is only a single peak in frequency spectrum. Our software needs to know what kind of input it is before taking action. So we ...
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24 views

How to get cofficients in DFT?

In my recent study of signal processing I came to know that we can compress images/signal using DFT/DCT. If we consider the lossy compression of audio or any image then it follows the same steps: ...
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1answer
40 views

How does “image synthesis” work?

I'm interested in how does "image synthesis" in audio synthesisers such as Metasynth work. Image synthesis is when a picture is read into a program and "interpreted" into sound. But how does it ...
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Low-rank approximation of the STFT matrix : good audio compression technique?

I recently heard about this interesting math tool: With a matrix $A$, compute the SVD ($ A = U \Sigma ^tV$ factorization, where $\Sigma$ is a diagonal matrix containing the "singular values") Keep ...
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Mask shape in image DCT transform

I've been studying image compression using the FFT and DCT transforms. When using the FFT transform, it is customary to perform a frequency shift (fftshift) so that ...