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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Implementation of goertzel algorithm in C

I am implementing BFSK frequency hopping communication system on a DSP processor. It was suggested by some of the forum members to use Goertzel algorithm for the demodulation of frequency hopping at ...
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1answer
530 views

Find “base” frequency of pulse wave

I have some samples that are read from a square pulse wave and I'm looking for a way to find the characteristics of this wave. It's a pulse wave, let $T_1$ be the non-pulse duration and $T_2$ to be ...
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2answers
954 views

Algorithm to detect if a spoken phrase matches a previously spoken phrase

I would like to create a very simple system that allows a user to train (once or multiple times) a spoken phrase (from 1 word to a whole sentence.) Then the (same) user would speak the phrase back, ...
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0answers
58 views

determining walsh function components of signal after passing through non linear process

When a sum of sine waves is passed through a non linear process, harmonics and intermodulation distortion products are created, which are visible when applying an FFT to the signal. This causes ...
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0answers
370 views

choosing windowing function for audio signal processing

Currently I am working on chord recognition, and get confused on several aspect. One of them is choosing windowing for reduce the spectral leakage. from what I read, hanning/hamming function is a ...
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3answers
1k views

How to get Instantaneous Magnitude for a Instantaneous Frequency From FFT?

My understanding if a frequency in my signal doesn't line up exactly with a bin, it is smeared over a few bins to the right and left. How can the instantaneous magnitude be determined? (do I have to ...
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1answer
210 views

period detection for a series of photons

I have a dataset which records the arrival time for a series of photons. I am using lomb-scargle method of scipy.signal to try to find some kind of period. Since the arrival time is random,how to ...
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0answers
5k views

1/3 octave spectra from fft

I have got a signal in frequency domain. This is a frequency response function from software, so I can do nothing about it and have to leave it in frequency domain. I want to transfer the data to 1/3 ...
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4answers
21k views

Efficiently calculating autocorrelation using FFTs

I'm trying to calculate an autocorrelation on a platform where the only accelerated primitive I have available is the (I)FFT. I'm having a problem though. I prototyped it in MATLAB. I am, however, ...
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1answer
109 views

It is possible to obtain non-zero padding fft from zero padding fft?

This is just a question out of my curiosity, normally we do not do this I have a x(n)=[1 2 3] ...
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0answers
127 views

How to properly express periodogram over analog frequency?

Assume a signal $x[n]$ with $N$ samples and its $N$-point FFT $X[k]$. Assume also the simplest power spectral density estimator: $$ S_x[k] = \frac{\left| X[k] \right|^2}{N} $$ With this estimator, ...
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140 views

Estimating and Improving the accuracy of fourier transform in the low frequency sector

I have a time series file which starts with 1 and then quickly tends to oscillating about 0.001. The time series has a resolution of 0.01s and has 10^6 sequential points starting from t=0. The goal is ...
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2answers
232 views

How to change the FFT phase domain of each frame by 90 degrees

I have read a signal in Matlab, resampled and implemented an FFT of each frame on it, now I want to rotate the domain of phase in each frame 90 degrees. I have a vector of FFT and used the function ...
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3answers
3k views

Filtering with STFT

I have sucessfully implemented a STFT (+inverseSTFT with perfect reconstruction of original signal, with overlap add, etc.) in order to work on audio files. Using this STFT / iSTFT framework, I have ...
4
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1answer
300 views

What sonic artifacts are caused by phase vocoders?

When using a phase vocoder to alter the spectral envelope of a signal, the input signal is split up into many (often hundreds of) bands. With many phase vocoders, the output levels these individual ...
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2answers
2k views

Filtering in frequency and time domain

I am trying to filter a sinusoid ($f_{sample}=50 Hz$) ,, i need to remove all frequencies above 10 Hz with accepted transition region 2 Hz (stop band freq=12 Hz) the question is why after filtering ...
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2answers
2k views

FFT, How to decide if there is a signal among noise?

I have sets of data of different deep sky objects. My job is to check for any periodicity. I use IDL to run an FFT and wavelet methods to check for a signal. To test my code I ran the IDL built in ...
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3answers
8k views

Why are magnitudes normalised during synthesis (IDFT), not analysis (DFT)?

In most examples and FFT code that I've seen, the output (frequency magnitudes) of the forward DFT operation is scaled by N -- i.e. instead of giving you the magnitude of each frequency bin, it gives ...
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1answer
176 views

What kind of discrete convolution is this?

Let x[n] and y[n] be defined for n=0,1, ..., N-1. This (for example with Python's scipy fft ...
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1answer
585 views

Reconstruct DWT for each cD1,cD2,cD3 and cA3 signals

This question must be basic for this forum, but I'm only start working with DWT recently, and I was working with CWT before. I ...
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2answers
124 views

Acoustic measure of a specific room

I would like to make an acoustic measure of one room, so I can compare it with a acoustic measure of some other room. Then compare these data. So when I take an acoustic measure of the first room ...
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1answer
314 views

A little bit better than zeroing bins in order to filter

The topic of zeroing frequency bins before IFFT has been discussed here : Why is it a bad idea to filter by zeroing out FFT bins? It was very helpful to understand why it is a bad idea. What do you ...
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1answer
89 views

Theoretical question on Fast Fourier

I have a question regarding Discrete Fourier Transform and Discrete Time Fourier Transform. Suppose that we have a sequence $x(n)= \{1,2,3,3,2,1\}$. So is it possible to reconstruct the Discrete ...
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2answers
161 views

How to do a spectral fade out?

I'd like to do a fade out of a sound in a few seconds, but in a "spectral way", with a special curve : (here x-axis is time, y-axis is frequency from a few hz to 20khz). All the part "to be removed"...
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1answer
17k views

Cross correlation with FFT and fftshift

When I calculate the cross correlation between two vectors with the following code ...
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4answers
4k views

Estimate frequency and peak value of a signal's fundamental

How can I find out frequency and peak value of a signal's fundamental? Please do consider the following: The peak value of some harmonics might be higher than that one of the fundamental The ...
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1answer
249 views

How to prove that Dilution of a time domain signal results in duplication in Frequncy domain?

While reading a description on FFT from this book, I found the following statement: ...diluting the time domain with zeros corresponds to a duplication of the frequency spectrum. How can I prove ...
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1answer
2k views

Performing classification based on FFT results

It is perhaps important to start with the fact that I am a complete beginner in DSP. I have got a number of audio recordings (of sampling rate 22 kHz) - of bird songs - which I have been trying to ...
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1answer
151 views

why if we pad any signal with enough zeros we can get the same result

if we pad any signal with enough zeros we can get the same result as linear convolution whilst using the fft function we compute circular convolution. Why?
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0answers
115 views

Denoise a randomly occuring signal

I have a program which takes in data from an oscilloscope, and due to reflections in the medium, we will get random signals at random intervals. The two grey windows at the right bottom show the ...
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3answers
497 views

FFT of a periodic function [duplicate]

Suppose you have N samples of a sine wave of frequency $f_0$ sampled at $f_s$. $$ x[n] = A\sin[2\pi(f_0 /f_s)n] $$ How do you get a delta function in the frequency domain (i.e. all of the energy is ...
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1answer
350 views

M-point FFT Amplitude of N-samples of a sinusoid

Suppose you have N samples of a sinusoid of frequency $f_0$. $$ x[n] = A\sin[2\pi (f_0/f_s)n ] $$ Suppose you take an M-point FFT (where M may be greater than N) of your N samples of x. What will ...
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2answers
1k views

How does one know how many times to downsample in Harmonic Product Spectrum?

I have been working on a Harmonic Product Spectrum Algorithm. Now, all the literature I've read about the subject tells me to downsample an N amount of times. How does one determine what this N value ...
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1answer
78 views

If I want to apply a filter to an Image should I use the IIR or FIR filters?

So I have discrete pixel values in the image and each row or column would make a signal. I would like to filter some of the rows or columns to remove high frequency components from them. Should I use ...
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1answer
196 views

How do you choose a size for a windowing function in FFT?

How does one choose the proper windowing function to apply in an FFT? What are the benefits of larger sizes and smaller ones? Which would be the best for pitch estimation? Also which window function ...
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1answer
281 views

How to detect specific behavior in time series?

I was not quite sure what the right SE for this was, so I posted this also here on SciComp. Please tell me which one to remove :) Problem statement I have a few hundred unrelated time series, say $...
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0answers
145 views

Causal bandstop filter

I have a vector of zeros and ones with length ~2000. I need to detect and filter out the once, that appear periodically. There may be none to 3 such periodic signal's components. Typical periods are ...
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0answers
656 views

What is the best pitch (frequency detector) for a Voice Activity Detection Algorithim?

I am programming a Voice Activity Detection algorithm. After researching several methods, I implemented a simple method that determines whether or not the person is speaking based off the RMS of the ...
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1answer
22k views

Why should one use windowing functions for FFT?

So I just revised my pitch calculation algorithm using a harmonic product spectrum algorithm. I was just curious about why this explanation of Harmonic Product Spectrum states that you need to ...
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1answer
77 views

Is there a general relation between mean power and period

I posted this question at Math Stack Exchange a few weeks ago without any luck. It occurred to me I might have more luck by posting it here. The basic question is whether there exists a known ...
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1answer
736 views

How to convert a filtered time-domain signal into frequency one? [closed]

I have a signal in matlab like this: I have designed a band-pass filter in 16-32 MHz range: and applied the filter to the signal, the result is like this : My Question: what is the easiest way to ...
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1answer
565 views

Are the DFT/FFT multiplications in the fourier domain complex multiplications?

If you want to compute a convolution with a DFT/FFT, you will have to do a DFT on the image and a DFT on the kernel. And you will need to multiply the spectrum of the image with the spectrum of the ...
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1answer
1k views

Using fft in matlab to retrieve input signal magnitude

I am trying to understand how you use an FFT in matlab to measure/retrieve the magnitude of the input signal. For my understanding I have put this script together, creating a 15Hz sine wave with a ...
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0answers
203 views

Constant phase for each frequency?

FFT of some signal $x$ has two parts: $|x|$, which is the magnitude spectrum and $arg(x)$, which is the phase spectrum. I want each frequency to have the same phase. Is there a way to accomplish this?
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2answers
92 views

DSP Topic for Newcomers

Does any one of you know what topic to teach people related to signal processing. The audience is mainly for a group of software programmer working on a telecommunication product who have limited ...
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0answers
76 views

Get excitation from two signals

I have two signals, one whisper data and one normal voice data of the same sentence. I'm trying to build a voice conversion, but just want to start off with some simple signal manipulations. I ...
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2answers
3k views

Confirmation on how to calculate phase differences at every frequency point between two wideband signals?

I have a problem that I thought was going to be simple, but it has become surprisingly stubborn and I question my method... I have used the method (described below), but I wanted to confirm that ...
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1answer
2k views

simplest Notch filter in the world

What do you think of this notch / band reject filter for a very very narrow band ? ...
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1answer
1k views

Guitar Tuner or Guitar effects Algorithms? [closed]

I need to explore the algorithm of the digital guitar tuner or the digital guitar effects algorithms. Is there any Book or articles that you recommend of? All I know is that relate to DSP. thanks
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1answer
2k views

Preparations to implement FFT on a wav file (code Java, not Library)

I am making preparations to implement FFT on a wav File.wav Only Java. I'm reluctant to use matlab I have a File wav stereo, 16 bits. I need to calculate the FFT, but I have confusing. My File has ...

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