Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [fft]

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

2
votes
2answers
57 views

How do MATLAB and/or Python treat $2^n$ samples rule in FFT

As far as I have read, an FFT requires that the number of original data points must be a power of 2. I'm wondering whether the tools like MATLAB or Python which have FFT functions take care of this ...
0
votes
0answers
41 views

Can Reassigned-STFT be an invertible transform? Algorithm for “Signal => Reassigned-STFT => masking => Reassigned-ISTFT => Output signal”

It is well known in DSP that this is a successful method to modify audio signals: Signal => STFT => masking => ISTFT => Output signal For example, ...
2
votes
1answer
123 views

What is about the circular convolution in OFDM

In an OFDM system, serial-to-parallel conversion for data is done, then the DFT is performed and then adding the cyclic prefix (CP). My question is related to that step of adding a CP. As I know, ...
2
votes
1answer
112 views

Separate two sinusoids with very close frequencies (5 Hz difference) in a 44.1 Khz audio signal, with good time-domain resolution [closed]

Here is an audio signal which is a mix of (WAV file available here): a 2000 Hz sinusoid, beginning at 1.00 sec, without fade-in/fade-out a 2005 Hz sinusoid, beginning at 1.031 sec, with a slow fade-...
1
vote
1answer
59 views

Time signal FFT different for whole signal than half signal on high frequencies

I have a time signal of u from 0 to 1000 time units. If I chop the signal in two halves and compare the frequency spectrum of both it looks similar, as it should (...
1
vote
0answers
16 views

artifact identification in irregular-samped data

There is a dataset combined by different datasets a,b,c,d,e. The time intervals are irregular(i1, i2, i3:intervals between a and b, b and c...), but the sampling rate SR in every single dataset is the ...
0
votes
1answer
138 views

Phase shift problem in Fast Fourier Transform

I try to make graph/print for magnitudes and phase shifts for impulse response calculated by FFT. For magnitude everything works perfect, but for phase shift I get some strange curve for higher ...
1
vote
1answer
251 views

Why am I seeing a negative frequency on FFT graph in Gnu Radio Companion? [closed]

I have a pretty simple flow here in GRC, but for some reason I'm seeing a negative frequency mirroring the 10khz signal that I'm generating. What's causing this negative frequency to show up in the ...
2
votes
0answers
109 views

Frequency translation with FFT

I'm new to DSP and I would like to make an SDR receiver. For this I want to shift bins in the frequency domain in order to bring to 0Hz any portion of the base band spectrum (I know that there are ...
1
vote
0answers
270 views

Remove a line in image with FFT

I would like to remove vertical line from an image (an example). I took a 2D FFT and try to apply a mask to suppress the line. Nonethelesse the approch is not very efficient, because i lose an ...
1
vote
1answer
180 views

Reconstruction of a signal from non-uniform samples [duplicate]

So I'm having some troubles with a signal that's been sampled but where the samples don't have consistent intervals. I've been looking into the NFFT (in python) as a starting point but I'm a complete ...
1
vote
1answer
238 views

Spectrogram with square or non-square magnitude of STFT: power vs. magnitude

As seen in this question and answer, to do a spectrogram, it's common to plot either: the square magnitude $|\text{STFT}(\text{frame}, \text{bin})|^2$ ("power spectrum") the magnitude $|\text{STFT}(\...
1
vote
3answers
58 views

harmonic algorithm for extending compressed bandwidth of audio file

I just found this site and feel at home :) I've been playin around with python and some compression ideas and was wondering if there's anything like what I am trying to figure out... I've noticed ...
1
vote
2answers
78 views

Relating phase difference in a signal with its frequency

I have a 134 point complex signal. Using MATLAB, I have observed that the phase difference between any two adjacent samples of this signal is 2 radians i.e. the phase increases linearly from 0 to 268 ...
1
vote
2answers
167 views

wrong output using numpy fft on a tone

I am getting the wrong output with the following simple implementation of Python fft. Can someone please explain what I need to fix? ...
0
votes
1answer
193 views

Image zooming with Fourier transform

I want to go from this image into this one: So basically I need to scale the white square. The authors of the paper claim that this can be done in four steps: zero-padding in real space (image is ...
1
vote
0answers
302 views

Acceleration time series to velocity conversion using DFTs

I have 1000 Hz time series data for acceleration (512 data points), which I want to convert to velocity. I am trying to use the omega arithmetic method to achieve this. Following are the steps I am ...
0
votes
1answer
116 views

Pitch detection algorithms “give up” after very little

I'm sorry if pitch detection has become a stale topic here, but I'm really interested if anyone has any advice on this topic. I'm looking for the best pitch detection algorithm for stringed ...
1
vote
1answer
83 views

Application of Parsevals theorem with Welch method

For my project I had to manually code the welch method using the code below. Pretty much it involves finding the spectral density through fft and incorporating windowing and segmenting with overlap. ...
0
votes
2answers
58 views

I'm confused about the notion of frequency when it comes to arbitrary data

In signal processing class we keep learning about how it's so useful to bring things into the frequency domain instead of the time or space domain but I'm very confused about what the motivation is or ...
0
votes
2answers
93 views

Window length in matplotlib's specgram

In the paper about speaker verification I can read that Two quantities have to be set: the length of the window and the shift between two consecutive windows. For the length of the window, two ...
3
votes
2answers
388 views

FFT vs DFT Run Time Comparison (Complexity Analysis) in MATLAB

So we were given an assignment to plot the time taken by the FFT algorithm by MATLAB and a DFT algorithm written by me in MATLAB.G The expected output should have been the DFT algorithm following the ...
0
votes
1answer
64 views

How to get the MLSEEqualizer work with IFFT and FFT blocks in the communication system?

Matlab MLSEE equalizer works fine with the QPSK modulated signal when the signal is propagated over the multipath channel. However, if there are IFFT and FFT blocks used at TX and RX sides, ...
2
votes
2answers
605 views

How to get around the circular shift property of Discrete Fourier Transform?

I understand that when we introduce a linear time shift using DFT on a finite sequence, the algorithm assumes that the signal repeats itself outside of the given range. Here is an example explaining ...
0
votes
2answers
160 views

Square Wave with Random Edge Shifting

I took a square wave signal and individually shifted all the rising and falling edges by a random amount of time, within certain +/- bounds (a random time for each edge, not shifting all edges by the ...
2
votes
1answer
47 views

Maximum of cross-correlation not moving

I already asked this question here yesterday, but it was very poorly worded I think. I made a much more detailled post explaining my problem of stackoverflow, as it might also be a code problem. Here ...
1
vote
1answer
105 views

DFT (FFT) of Non Uniformly Sampled Signal

I am trying to perform an FFT of a non-uniformly sample signal. My input comes from Simulink and PLECS which uses variable-time solver. So far, I have used ...
0
votes
1answer
500 views

Computation of the Inverse DCT (IDCT) Using DCT Or IFFT

Is there a way to compute the inverse discrete cosine transform (type-2) by leveraging either a DCT, FFT, or IFFT algorithm? I have seen ways to compute the DCT using FFTs, and I've seen ways to ...
0
votes
1answer
94 views

Emulating a Variable Delay

I am trying to emulate a satellite link where the delay time between the satellite and ground station changes over time due to the satellite's motion. I plan do this by converting to the frequency ...
0
votes
1answer
61 views

Extracting positive frequencies of discrete-time signal

Convolution in the time domain is the same as multiplication in the frequency domain. My data is sampled at 200 Hz, which means that the Nyquist frequency is 100 Hz, and all frequency content is <=...
3
votes
3answers
329 views

Calculate ifft using only REAL forward FFT

There are already questions on this topic here and here. I am trying to calculate the ifft using a DSP that only has a library function for a forward REAL (assumes conjugate symmetry) fft. For a given ...
1
vote
1answer
90 views

How to calibrate a signal with respect to frequency

I have recordings from accelerometers (non-flat response with respect to frequency) and I'd like to convert my voltage time series into acceleration values. Is there a standard method for doing this? ...
0
votes
2answers
289 views

Orthogonal signals in frequency and time domains [closed]

I have 3 orthogonal signals obtained by Fourier transformation. But when I do the inverse Fourier transform in Matlab, my signals are no longer orthogonal in the time domain. Here is my question: ...
1
vote
1answer
346 views

Seven term Blackman Harris window

I am currently trying to evaluate a high resolution ADC for which I need to window my output data for the FFT. Up until now I have been using the default 4 term Blackman harris window in MATLAB. ...
1
vote
2answers
77 views

A question about Gibbs phenomenon example in Richard Lyons book

If anyone has a copy of this book could you please shed some light here: I was trying to reproduce the example shown in Chapter 5, section 5.3.1 Window Design Method's Figure 5-19 which illustrates ...
1
vote
1answer
67 views

Perform overlap add with available FFT size smaller than filter coefficients

I would like to process 12 to 20 seconds of incoming audio at a sample rate of 44100. I must process this audio in real time in an STM embedded kit (perhaps also an Android Smartphone). I'm trying to ...
1
vote
2answers
225 views

Linear Convolution in DSP and Hann window

My understanding is that when dealing with discrete finite sequences, convolution done thru FFT is circular. To obtain linear convolution, one would pad the input with zeros up some appropriate length....
1
vote
1answer
63 views

The complexity of zero padded DFTs [closed]

Assume that I have L points and want to calculate its Fourier transform with N points (N is much larger than L, link N=256, while L=10), I am think if there is way to calculate it with lowest ...
0
votes
1answer
61 views

FFT High Frequency Humps

I am using Matlab to take the FFT of a series of pulses. Can anyone explain why there are multiple humps at high frequencies rather than a smooth roll-off?
0
votes
3answers
110 views

Efficient calculation of exact frequency from a broad frequency range (1 Hz - 1000 Hz)

I have some input signal sampled at 1-10 MS/s. Let's assume that it contains one strong frequency component (with frequency anywhere in the range from 1 Hz to 1000 Hz or even higher, changing over ...
1
vote
1answer
87 views

Calculating THD where peaks are not exact harmonics

I have captured an FFT of a 1 kHz signal that I am generating using a WM8904 codec running at 48k samples/second connected via I2S to a ARM microcontroller (Atmel SAME70). It appears to have some ...
-1
votes
1answer
133 views

Spectral Subtraction python implementation error

I am trying to implement Spectral subtraction in python. I am new to DSP. I used this article as reference and below code is what I can come up with. Of course I did not get the expected output. I ...
0
votes
0answers
63 views

Comparing Octave/Matlab FFT results against CPU FFT

I wrote a program which runs FFT from Intel MKL and am trying to compare its results with that of Octave, but things don't quite match. The program does: Populates a 1D array of, say, 1024 elements, ...
1
vote
1answer
614 views

Amplitude of frequency bin in FFT doesn't match time-domain amplitude

I have a sinusoidal current that I am sampling at about 357k SPS. The current signal is about 3A pk-pk @ 750hz (top figure). I am wondering why when I take the fft using numpy/scipy's fft function, ...
1
vote
3answers
411 views

How do I calculate peak amplitude of the signal components after zero padding and FFT?

I am learning about DFT and trying to apply it to some audio processing. I am new to DSP but experienced in programming and have some background in math and physics. The FFT algorithm I use (lomontFFT)...
0
votes
2answers
182 views

Software to extract frequency spectrum data from an audio file

I've been trying to learn how computers recognize musical notes, and I found apps like spectrogram which shows the frequency spectrum of a sound, but what I need is the data which is plotted or the ...
1
vote
3answers
278 views

Denoising a signal

I'm starting hydraulic experiments, where I'd have to measure velocity in an unsteady flow with a device called Acoustic Doppler Velocimeter. In DSP terms, I'd have a nonstationary signal in a shape ...
2
votes
1answer
67 views

Small shift in frequency in FFT

I'm trying to compare the estimation of the power spectral density (in this case of a fake cosine signal) by two different methods: 1st, MATLAB's fft function, and 2nd, a direct calculation from the ...
0
votes
1answer
76 views

methods of crest factor minimization

i am studying the methodes CF minimization. and have a doubt. in each methods there are steps with DFT and IDFT or like this FFT and IFFT. Everyone provides the fact, that they use DFT and IDFT for ...
0
votes
1answer
199 views

How can I show DTFT result in MATLAB? [closed]

I wanna show DTFT result and convolution result in f-domain are same. Additionally, I wanna show sampled function and inverse fourier transform result are same too. How can I show this? If I use ...