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

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38 views

Note detection in an audio file.

I am trying to find the given note in an audio file. It has been specifically told that each file contains only one note. So i directly took fft and found the corresponding frequency and then mapped ...
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1answer
42 views

What Is the Point of Doing the Zero Padding? [duplicate]

What are the advantages and disadvantages of doing Zero-padding, in particular the case of speech signals?
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0answers
15 views

Recover signal after windowing and STFT [on hold]

I've implemented a STFT algorithm to apply it to speech signals and I have a couple of questions. 1) How can I apply the zero-padding? I keep reading that people do it but I don’t really ...
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0answers
23 views

Unexpected behaviour when using a Hamming window during FFT

I'm trying to get a smooth signal in the frequency domain of a pressure signal I've computed using a Hamming window. This is the code I'm using: ...
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1answer
55 views

What determines the accuracy of the phase result in a DFT bin? [closed]

What are the factors that affect the accuracy and precision for the phase that is given by the DFT? Just thinking medium-hard about this, it occurs to me that it must have something to do with the ...
1
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1answer
28 views

Calculating SFDR from FFT of ADC output

A few months ago, as part of my summer internship, I had performed interfacing of an ADC with FPGA (Zynq-7000). The goal was to take an analog signal from a signal generator, feed it to the ADC and ...
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2answers
37 views

Accurate description of the spectrum of sinusoid waveform added with WGN?

The transmitting signal is $$ s(t) = \sin(20\pi t)+\sin(40\pi t)+\sin(60\pi t) $$ The received signal after AWGN channel is $$ r(t) = s(t)+n(t) $$ where the variance of noise $n(t)$ is $\sigma^2$. ...
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1answer
19 views

problem finding 16 point DFT using two 8 point FFT (Divide and combine algorithm) MATLAB [closed]

Write MATLAB code that determines and plot the N-point Discrete Fourier Transform of x[n] defined by the following equations: x[n]=0.5*pi*n n=0:16 Compute and plot 16-point DFT using two 8-...
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29 views

DBPSK Implementation in Python [duplicate]

I am implementing DBPSK as a hobby project in python. I want to encode binary data into an audio signal then transmit the signal over speakers to another device where the signal will be captured with ...
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2answers
39 views

How to plot and normalize a spectrum in matlab

I am given the coefficients of an FIR filter. I have created its impulse response through a convolution with a unit pulse. Now I want to plot the frequency spectrum. I perform zero-padding and ...
1
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0answers
34 views

Frequency bins too powerful at the start and at the end of each sample computed DFT data

I've taken the following link http://coding-geek.com/how-shazam-works/#comments as a project to start practising and learning signal processing and python programming for me to get started in speech ...
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0answers
17 views

MFCC feature vector

I want to extract the MFCC feature vector of PCM data into a wav file. Is there a way to extract pitch intensity from MFCC feature vectors?
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2answers
79 views

Choosing sampling frequency and base interval to eliminate leakage

I'm studying for an exam and have some trouble with an exercise. So I have a continuous-time signal that is $$s(t)=\sin(2\pi f_{s1} t) + \sin(2\pi f_{s2}t)$$ with $f_{s1} = 1.4\text{ kHz}$ and $f_{s2}...
1
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1answer
31 views

Perform non-power-of-two FFT using ARM CMSIS library

I have 1280 points which I would like to perform an FFT using a M7 cortex with hard floating point engine. As the title suggest I would like to use the ARM CMSIS library to perform a non-power-of-two ...
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1answer
40 views

How can I get the power of a specific frequency band after FFT?

I need help with my matlab code. I have recorded EEG data and now I want to analyse it in matlab. I want to find the mean power of specific frequency ranges (theta: 4-8 Hz,alpha: 8-12Hz etc.). For ...
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1answer
40 views

Spectrogram Interpretation

I collected vibration data (amplitude and time) on a component that was attached to an engine. Using MATLAB I plotted a spectrogram to see what frequencies it vibrated at. The code: ...
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0answers
11 views

what does mean that sub-channel must not share common zeros

In blind channel identification, using SIMO channel or oversampling, a very common and known condition is supposed which is: "Sub-channels must not share common zeros", in other words channel must not ...
1
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1answer
53 views

OFDM Simulation process

I'm trying to understand OFDM by making a simulation. Are these steps correct? generate M random complex QAM symbols. example: (1+j,1-j,-1-j,1-j....) Split my M samples into a N 2048 sized arrays ...
1
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1answer
32 views

Why delete high frequence in fft return the area of the most changes?

I'm new to ||image-processing|| and || fft filters || I have a relative smooth $\mathtt{2D}$ (circle) gaussian surface (height $10$) with several "holes" in it, and the surrounding area [has] some ...
1
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1answer
42 views

Fast Fourier Transform using numpy

I am a computer science student and didn't really have signal processing as a subject. Maybe I should be clear on the concepts of sampling rate and frequency of the signal but I am a little confused. ...
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0answers
19 views

Indexing problem with using FFT convolution to remove echo

I've been using a very basic kernel to remove a known echo from a signal via convolution in the time domain e.g assuming a signal contains a delay of 5 samples ...
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votes
0answers
12 views

DTW MFCC pronunciation similarity

There are two wav files with the same word recorded. To compare this, we extracted the wav file pcm, MFCC (Mel frequency factor) and obtained the Euclidean distance value through DTW. (1) and (2) are ...
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1answer
25 views

Question based on scaling the FFT for obtaining PSD

Following is the code given in MATLAB's site to estimate PSD using FFT. ...
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0answers
20 views

FFT and correlation between two signals for word detection

I have a task where I am supposed to make a python script for word recognition and I am not allowed to use any high order python commands without the fft and ifft command. The audio signal is ...
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2answers
57 views

Shifting signal smaller than discrete step

I have a image that I need to shift with less than a pixel. My plan was to do a Fourier transform and multiply the signal with $e^{-aiu-biv}$ where $a, b$ are the shifts in x and y direction. This ...
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0answers
38 views

Stability in evaluating real part of a Fourier transform

I posted this on maths stack exchange but realised it might be more appropriate here. So forgive the cross posting! I have a signal $S$ and want to evaluate the magnitude of the real part of it as ...
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0answers
39 views

what are the advantages of using Lomb-Scargle over FFT?

I know that lomb scargle is used for non uniformly distributed timepoints, but assuming we had those, Is there any difference between using Fourier transforms and Lomb Scargle. I know this is a ...
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0answers
20 views

Common Cyclic prefix for a set of cascaded OFDM symbols

I've seen research papers / baseband systems that deal with synchronization using a common CP(Cyclic Prefix). The transmission structure comprises , a family of complex orthogonal sequences, with ...
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0answers
18 views

detecting rhythmic behavior in damped oscillations

I have a time series data that, upon visual inspection, reflects a periodic oscillation. However, this oscillation seems to follow a damping behavior. What do you suggest as the best methods to verify ...
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0answers
20 views

dsPIC33E ADC to FFT help

I am sampling an audio range signal with a bandwidth of 3100Hz and then applying a FFT using the DSP library example from Microchip to determine the most dominant frequency of the signal. On the last ...
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2answers
64 views

Why is my DFT/FFT always 90° out of phase?

I'm doing an FFT using Python and Numpy on one machine, and C# on another. I'm using some dummy data that mimics how I'll eventually be gathering data from sensors in the C#/UWP application. The two ...
1
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1answer
60 views

Damped sinusoidal form FFT of signal

I'm doing an assignment for the course Signal analysis where I have to analyse a signal. I've tried quite some things now but it's still bothering me that the FFT is looking weird, and not looks like ...
3
votes
1answer
50 views

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

I would like to optimise FFT algorithm by only using a FFT of size $N/2$ to transform a real sequence of length $N$. There are already many questions and many excellent answers on the matter (here for ...
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1answer
46 views

Attenuate frequency bin in FFT array resulting in artifacts

Am trying to remove noise for certain frequency bands by attenuating freqeuncy bins in the FFT array. However this results in artifacts to be formed, where there are clicking sounds in between each ...
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1answer
44 views

How to determine the original size of the FFT used in unknown OFDM symbol

Given an unknown OFDM symbol consisting of 9144 samples, interested to know the size of the FFT used in the TX/Number of bins. Down-sampling to 512,256,128,64,32 yields the following. Do not see how ...
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1answer
63 views

If my sampling rate is not high enough to capture all frequencies, can I accurately capture low frequencies?

Let us say that my sampling rate is 1000 Hz. This enables me to accurately capture every frequency in the 0-500 Hz range according to the Sampling Theorem using a DFT. However, there are higher ...
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vote
1answer
79 views

Two voice pronunciation comparison similarity MFCC + DTW

Calculate each MFCC to compare wave file A and wave file B, and then use FastDTW to measure the distance after two sets of MFCCs. We compared the four wave files and obtained the Euclidean distance ...
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1answer
40 views

What is the proper way to implement a real time spectrogram?

I am trying to implement a real time spectrogram and I am not sure that I am implementing it the right way. First I decided to use Matlab, I was taking a short recording of lets say 0.1 seconds and ...
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0answers
24 views

fastDTW voice pronunciation comparison question

Calculate each MFCC to compare wave file A and wave file B, and then use FastDTW to measure the distance after warping between two sets of MFCCs. I compared four wavefiles but got a distance value. ...
1
vote
1answer
37 views

Break a signal into segments, add them together and then perform an FFT on the result

If you break a 4 second signal into 0.5 second segments, add them together and then perform an FFT on the resultant 0.5 second data. Will the FFT / frequency spectrum be the simlar to an FFT on the ...
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1answer
47 views

frequencies in sound: multiple possibilities?

First, I am by no mean a sound engineer (as you will guess later). I was just wondering something while looking at the waveform of a .wav for a given shape of waveform on a duration of 2 sec for ...
1
vote
1answer
51 views

Is sparse signal in time domain is sparse in Frequency domain

In OFDM system, if we have a multi-path environment, we supposed to have a sparse received signal in time domain, then $FFT$ is performed to convert it into frequency domain. My question, does the ...
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0answers
12 views

Constants in Triangular Filter Bank

In various implementation for the triangular filterbanks for MFCC computations, I see the following constants but they are not commented/annotated. E.g. in https://github.com/alvations/...
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0answers
42 views

Create a frequency spectrum from a sequence of event times

I have a sequence of event times with non-uniform intervals between events and I'd like to get a frequency spectrum from these data alone. I imagine I could create a waveform that peaks at these times ...
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0answers
40 views

FFT - How to calculate real phase shift

When I calculate from FFT the phase shift like that: atan2(fft.imag(),fft.real()) * 180 / M_Pi It always gives me the value between -180° and +180°. And when ...
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0answers
43 views

How to get the amplitude of each frequency inside a bin?

if some frequencies enter inside a bin, how do I get the amplitudes of those frequencies?
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1answer
19 views

Defining frequency axis for periodogram

I am trying to simulate example 8.2.2 from Hayes, Statistical Digital Signal Processing and Modelling, on MATLAB. Let $x(n)$ be a WSS process consisting of random phase sinusoid in unit variance. $$ ...
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2answers
46 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 ...
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0answers
21 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
85 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, ...