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

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time domain data into FFT using Matlab

I do like to generate the FFT from time domain history data (experimental lab) using MATLAB. I am not so sure if my coding is right? Can someone verify the coding. My code is as follow: ...
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23 views

Apply FIR filters to Extract Stego from WAV data

I appreciate anyone that takes a moment to help me with this problem. I've been banging my head against the keyboard for a while, searching forums and DSP tutorials and I can't figure this problem ...
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40 views

What is the correct inverse function of the Matlab function fft? [on hold]

I used the Matlab function fft but I am not sure which function is the correct inverse to go back to the time domain.
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39 views

Fixing my FFT Plot

I'm trying to plot my FFT of File. This i my result. I made my FFT application: I want to obtain something very similar to plot of WaveSpectra, please tell me my mistakes.. My FFT The result from ...
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23 views

Matlab coding for bandwidth interval

I have time domain history data. Then, I convert it into FFT to get the frequency domain history data. The problem is, how to determine the bandwidth of the FFT data? Is it automatically synchronize ...
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20 views

Noise Removal from an image

What type of filters can be used to remove Poisson noise in an image? I tried applying Gaussian filter to few points in the spectrum.
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78 views

OFDM transmitter bandwidth

Theory Suppose an OFDM transmitter with four subcarriers is implemented using the structure shown below. If the serial data input rate is 40 bps, each parallel stream will run at 10 bps. ...
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1answer
55 views

Real valued FFT in Matlab

I'm trying to compute FFT of size (N/2) for sequence of real values of length N. I'm using this recipe. Here is my code in matlab: ...
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0answers
18 views

Relationship between FRF, FFT, AutoPower, & CrossPower

Given A is an input signal & B is an output signal: I know that the frequency response function (FRF) is defined as the CrossPower of AxB divided by the AutoPower AxA. Logic tells me I should be ...
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28 views

Applying a custom filter to FFT results?

I think I am missing something here and I do not quite understand why. Background: I am collecting quadrature signals from a software defined radio. There are two signals, the I, and the Q which is ...
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1answer
46 views

Phase difference between two sinuisoidal signal

Currently, I have two signals, the main components of both signals are 60Hz, but both also have weaker response at 180Hz + small amount of noise. As shown in the photo below, I want to find the phase ...
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1answer
32 views

Energy and SpectralFlatnessMeasure taken for PCM audio VoiceActitivyDetection

I'm trying to implement the VAD algorithm in this paper: http://ms12.voip.edu.tw/~paul/Papper/Steganography/iLBC/(VAD)Real-Time_VAD_Algorithm.pdf I'm polling a microphone on an Android phone, and ...
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36 views

Formulas to plot Frequency Impulse Response Coefficients

I made this question newbie:Plotting FFT and Impulse Response Coefficients, using Java I have the IRC: Impulse Response Coefficients: $h(k), k = 0, 1,.., N-1$ Low Pass: ...
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How to deal with the implications of sample Size for the FFT in Low Frequencies

I'm trying to detertmine presence of low frequencies, but I'm working from the tone 40 (82,4 Hz) until tone 84 (1046,5 Hz). With difference between one tone and its adjacent of Pow(2,1/12). Then ...
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1answer
31 views

Has anyone used Siglib? Answer a question on the FFTr function?

I'm hoping someone - anyone can answer a question on the Siglib library call to perform an FFT on data. There's no examples anywhere I can find that provide a real application using data from an ADC, ...
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2answers
40 views

Spectrogram of a chirp and its FFT

This question follows from an answer to this other question: Conceptual question on FFT and chirp signal I wrote a code starting from the spectrogram to compare it with the FFT result. ...
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1answer
26 views

How to narrow the frequency band of a wavelet

I have a ricker wavelet with a dominant frequency of 15 Hz. The fourier transform shows its frequency band is almost to 50 Hz. How can I narrow the frequency band of this 15 Hz ricker wavelet? I ...
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3answers
75 views

How to determine SNR from FFT of measured data?

I am doing impedance measurements, where I do a frequency sweep of a test current, and I measure the resulting voltage. Offline, I compute the FFTs of the voltage and current, and I want to make sure ...
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1answer
55 views

FFT: Removed padded zeroes?

I have an application where I do this: DFT->Filter->IDFT on a range For computational performance I'm zero-padding my FFT to a power of two, but when I ...
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3answers
63 views

detect impact from digital audio

I've started a hobby project which is to detect and count the number of impacts (for example someone clapping, bouncing a ball or hitting a boxing bag). I've been reading and playing around (in java) ...
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2answers
64 views

FFT Overlap in Matlab

I am getting incorrect amplitude of my signal post FFT (90% error) and it does not improve after applying any of the window functions prior to FFT. After reading a number of articles, I believe FFT ...
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1answer
69 views

Conceptual question on FFT/IFFT (IFFT existence)

I was reading "Discrete and continuous Fourier transforms: analysis, applications and fast algorithms" written by E.Chu and, at some point, I found something that I could not completly understand. ...
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2answers
69 views

Using only positive frequencies in fourier domain, How will it affect the ifft?

I am going to do some kind of transformation and transform a data to another domain, and again back to the first domain. For this, I take a fourier transform of the data and separate the positive part ...
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111 views

system response: time vs frequency. Why do I get different magnitudes?

I am simulating a linear system described by the following equation $m \ddot{x} + c \dot{x} + k x = A \sin(\omega t)$ ...
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90 views

Is it necessary to apply some window method, to obtain the FFT? Java

I read that the window is needed to apply filter (Low Pass, High Pass, Band Pass or band Stop), but not for the FFT. 1. What advantage does apply a window or disadvantage does not apply? 2. What ...
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22 views

Compute the impulse response from analog frequency response sampling

I want to compute the impulse response of a linear analog system. I have measured the frequency response of this system, say $H(f)$, at many frequency bins(fixed step size), and obtain a vector ...
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63 views

FFT calculation suitable, Wav File, Java

If I have a wav file with this characteristics: 16bits (2 Bytes per Sample) 32000 Sampling Rate 60 Seconds 2 Channels then I have: ...
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19 views

DCT-I with FFT Power of 2

I have a bit of a problem, I am trying to calculate DCT-I which is easily obtained by 2N-2 FFT and taking the real parts. However my FFT library only supports power of 2 FFT's. Is there anything I can ...
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56 views

How to determine cut-off frequency using power spectral density?

I am new to DSP and my question is a very simple one. It is about determining the right cut-off frequency. I calculate the power spectral density using FFT by Welch's algorithm. However I am confused ...
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1answer
100 views

Can I take piecewise FFT of a larger input sample?

I have a N point sequence x. Let X be the fft(x). (Assume x is arbitrary) where, x=[x1 x2 x3 x4 x5 x6 x7 x8] fft(x)=[X1 X2 X3 X4 X5 X6 X7 X8] How do I get the ...
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1answer
55 views

Sub pixel shift causes weird results

I am trying to shift an image on a subpixel level, with the method described here: ...
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26 views

Choosing the frequency for a comb filter

I have an audio sample. From doing FFT on it it looks as if I need to use a comb filter to remove resonant frequencies. This is what I generate: I honestly have no clue where to start ...
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1answer
98 views

Why does FFT generate a jaggedy signal

I have an application that fills a buffer from my computer's microphone and does an FFT. My objective is to figure out what frequencies are in the sample. I've tested the application by whistling as ...
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1answer
41 views

The Nyquist-Theorm behind the fft

I saw a code in Python in the scipy.org (http://docs.scipy.org/doc/scipy-dev/reference/tutorial/fftpack.html) and found this: First question: Is it right that T = 1/800 <==> fs = 800 Hz fulfill ...
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29 views

How to simulate two OFDM Users with low complexity FFT/IFFT?

have two User one of them sending over freq (0-B] and the other transmit over (B-2B]. Both of them are using OFDM and each one has Nc subcarriers. I wanted to simulate the received signal using ...
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3answers
112 views

What is the difference between general microprocessors, DSP and FFT chips?

I know that a general purpose microprocessor requires 18 operations to perform each butterfly of the FFT, but I do not understand how does using using a DSP or FFT chip improve FFT processing? Any ...
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1answer
37 views

What is the distance metric in dynamic time warping?

I am reading the lecture slides from this site http://luthuli.cs.uiuc.edu/~daf/courses/CS-498-DAF-P/Lecture%2018%20-%20Time%20series,%20DTW.pdf In slide 24, the lecture suggest using metric of the ...
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1answer
43 views

Why do we need to normalize a WAV file before calculating the FFT?

I am trying to calculate the FFT of a signal stored in a WAV file using SciPy. I found a solution here, but it seems like we need to perform this step before the FFT: ...
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3answers
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Why does an 8 point DFT behave differently from a 16 point?

I have a 50 Hz sine wave sampled at 1600 Samples/second.I'm computing the 16 point DFT.So my fundamental frequency is 100 Hz. I then decimated the 1600 samples to 400 samples.I then computed the 8 ...
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Windowed FFT vs Morlet

I wonder if there is a difference between taking a Wavelet Transform on a signal s using a Morlet Wavelet w (i.e. correlation between s and w) and taking the Fourier Transform on subsequent parts of s ...
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48 views

Filtering of accelerometers data for double integration

This question in strictly related to this one http://scicomp.stackexchange.com/questions/16057/numerical-integration-and-filtering-of-acceleration-experimental-data but in this case I would like to ...
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2answers
57 views

Singal processing for undersampled signal

I have got a set of pressure data from a boiler which has been sampled at 45Hz and I need to extract a frequency component of 250Hz from the signal. Using a standard FFT method doesn't display ...
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1answer
37 views

FFT scaling in GNU Radio

In GNU Radio Companion, I have created a very simple flow graph where I generate a 1 kHz, 2.0 volts peak-to-peak sine wave, and feed it into an FFT sink and a time domain sink. The reference dB in ...
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44 views

How to, efficiently, identify telephone number from the key pressed data audio file?

A very common homework question. You are given an audio file(.wav) which has the recording of the keys pressed during a telephone call. You have to identify the telephone number from this audio file ...
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86 views

Detect Frequency of Incoming Audio on Raspberry Pi

I've been lurking around these forums for a while and they've been a great help to me in the past. However, I've been researching this problem for the past 2 days or so and can't seem to find a ...
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41 views

Reducing latency due to FFT windowing for a real-time signal

I need to compute the amplitude of a certain frequency band as the input to a PID algorithm. My system looks like this: ...
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0answers
23 views

Best way to reduce data to its symmetric and antisymmetric components

I have some noisy data that looks like this: I want to find the components that are symmetric and antisymmetric with respect to magnetic field. The first thing I tried was just using: Symmetric ...
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Find Short Clip of Audio Within Longer Clip Of Audio

I need help figuring out a way to automatically synchronize two audio files that are both different recordings of the same source. More info below. This example is from a concert, where there is ...
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1answer
60 views

FFT widow to dsp processor. ff meaning fft

I am applying 8 samples and triangular window to my fft engine. I am getting the results but not accurate (approximately equal with some tolerance). I am calculating MATLAB reference as below : ...
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How to design a filter with custom group delay — why is it an IIR?

Say I have an FIR filter with desired magnitude characteristics. I could imagine using an allpass IIR in series with the FIR to alter the group delay characteristic to provide both a 'magnitude ...