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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140 views

Correct scaling for AWGN noise in OFDM system after adding Preambles

I have a two-part question: Question 1 I wonder if anyone can explain about the scaling factor that is used for AWGN noise in OFDM system. For example I know about the scaling factor for normal OFDM ...
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59 views

Real-time DAQ (Data AcQuisition) device and filtering of voltage signals in audio frequencies

I'm working on a frequency mixer project in which two analog voltage signals at two different frequencies (each <5 kHz) are considered. I'd like to add the two fundamental frequencies and return an ...
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198 views

How to use frame based audio features for machine learning

I have an audio recording (wav file) that is 2 seconds long. That is my sample and it needs to be classified as [class_A] or [class_B]. To extract MFCC features, I divided the sample into frames (183 ...
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415 views

Window size and DFT size

I am using pwelch function of Matlab which returns the power spectral density (PSD) estimate. This got me confused about DFFT size and Windows size. Here my code: ...
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321 views

Filter image in Fourier space imaginary components after ifft (R)

I want to high-pass filter an image in Fourier space. It works but the retransformed image has an imaginary part, what shouldn't be the case http://math.stackexchange.com/questions/867337/how-to-...
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572 views

Get spectrum from autocorrelation function using fft()

I would like to observe Fourier Spectrum, got through Autocorrelation function. This is my code: ...
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129 views

Feature recognition within a single song

I want to write an algorithm in C++ which is capable of identifying specific features within a single song, e. g. the sound of a drum which is played 100 times during 5 min. State of the project So ...
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0answers
60 views

One period with transient

Assume I have only access to only one period of a signal that there is a transient effect on the signal as well. I am pretty sure that there is a particular frequency in the signal. Is there a way ...
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157 views

Zero padded-OFDM signal?

Why do we need 2N-FFT at the receiver when we want to demodulate ZP-OFDM signal ?
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33 views

Perturbation test for a real plant

How should we conduct a perturbation test for an LTI unknown system by perturbing the input to see the output response i.e. How many different perturbation step size should be given to the input?
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0answers
201 views

Efficient computation of Chirp Z Transform

Chirp Z Transform (1, 2, 3) is more powerful than zooming techniques (I use it to actually trace non-stationary chirp signals) and very usable in signal processing, but it's flexibility comes at price ...
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0answers
112 views

Are wavelets for audio spectrograms available as a simple FIR filter?

I have read that "Debauchies Wavelet is simply a short FIR" so i am searching for a single FIR that i can make into a filterbank, a precise "bandpass filter" that detects narrow frequencies, i.e. 1Hz ...
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2k views

How to design an interpolated notch filter in Python to filter powerline harmonics

I have a a time domain data set that records the magnetic field vs time, which must be processed to reveal an embedded signal. This data also contains power line harmonics (i.e. multiples of 60 Hz) ...
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88 views

Window function on large arays

Hello I'm reading the following document to better understand windowing and how to use it. "Spectrum and spectral density estimation by the Discrete Fourier transform (DFT), including a ...
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326 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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120 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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43 views

Is there a way to go from a set of (F/D)FT values to FIR coefficients?

I'm not yet well educated on the DSP subject, but I've initiated a project where I will do some audio filtering. My intuition tells me that there is a link between the coefficients of a FIR filter and ...
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380 views

Short VHF pulse detection from SDR

I need to detect a short (10ms) VHF pulse that occurs every 1.5s at a specific frequency (e.g., 150.20 MHz). I have an SDR that support IQ sample rates up to 10MSPS but due to computing constraints 2....
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417 views

How to compute DFT of IIR

This question pertains to frequency domain filtering. I'd like to multiply an IIR filter's frequency response by a buffer of samples that have been FFT'd. I get how I'd evaluate an FIR, I'd FFT and ...
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138 views

Averaging different frequencies

How does one average a group of frequencies? Frequencies taken for example using FFT. That is, given n frequencies over m time intervals (n $\leq$ m), how should one "interpolate" between those ...
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567 views

Subtracting one FFT from another for noise reduction

I am using an FFT/iFFT library in c#, and working with arrays of audio & complex data. What I am hoping to do is take a small amount of 'background' audio signal, and use it as a fingerprint to ...
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250 views

sound FFT data to PCM data

I have some FFT data, 257 dimensions, every 10 ms, with 121 frames, i.e. 1.21 secs. I think the first dimension is probably something else and the remaining are the FFT coefficients, I guess. From ...
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71 views

Is negative frequency important in calculating Spectral Moments

A follow on question form this one (What is meant by "spectral moment"?) In answers to the above referenced question spectral moment is defined as: $$ m_k=\int_{-\infty}^{\infty} f^k|X(f)|^...
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2answers
1k views

How do I perform Spectral Analysis (FFT, Windowing, Detrending) on Sonic Anemometer Data?

I am having trouble with all of the forums that I have looked at thus far. I have one day's worth of Sonic Anemometer data. I want to see the spectral analysis of this data. When the anemometer data ...
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0answers
551 views

Overlap add / overlap save using FFTW

I'm working on a realtime FFT processing algorithm in C using PortAudio. Currently I'm just trying to test if I can do OLA / OLS in (semi) real time using FFTW. I'm getting some distortion in the ...
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2k views

Compare two voices and outline their similarity

I am trying to develop an application which records the voice of someone through a microphone. I will have a preset recorded voices for the same words. I then need to compare the real time recorded ...
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594 views

How to process the .wav file to get meaningful information like the number of inhales/exhales

The plot of the data from the wav file. Link to the sound file - https://drive.google.com/open?id=0BxAPlY66uX7qWWtDZUw3WkpjSGs&authuser=0 Also the FFT plot is like this I am new to the field of ...
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80 views

Measuring typical seperation between patches using 2D Fourier Transform

I need to extract information about the typical distance between the black patches in an image like the one I attached here. Typical distance would be the the most frequent separation between two ...
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1k 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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1answer
127 views

Question About Linear and Circular Convolution - 1D and 2D

We know that applying a filter on an image is called correlation or convolution depending on the filter angle. In Gonzalez I have read that we can apply linear convolution on an image. Here I have a ...
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505 views

How to estimate PSD, and time delay of a random signal?

I'm trying to estimate the power spectrum and time delay for random signals. the signals were taken from two sensors, 10 cm apart. My aim is to estimate the PSD first then estimate the time delay in ...
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440 views

Using Fourier Transform on Gyroscope

The original idea is to calculate distance from accelerometer input. However, accelerometer reading also contains the gravitational values, thus to remove gravity, I tried using Gyroscope. The idea ...
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153 views

filtering out specific waves in scattering pattern

I have the following (experimental) image, with its correponding raw data in .csv format here. The pattern represents the scattering of a laser field off a point defect located in the center. One can ...
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94 views

Can the Fast Fourier transform be used to compute the magnitude of moiré

I am experimenting with image down-sampling and would like to calculate a numerical magnitude for alias-induced moiré patterns. Is it possible to do this by analyzing the frequency-domain (FFT) of ...
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367 views

Extracting features from a signal: a 21st century approach?

I have a discrete signal of random length (let's say between 500 and 800 in time). This signal has an important information which I want to collect and to put it together in a feature vector to train ...
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96 views

transmitting data using phase modulation of two sine waves passed through distortion

I have two sine signals with frequencies f1 and f2, and phase p1 and p2. I modulate the phase of these signals to transmit two symbols simultaneously, chosen from the set [0,1,2,3]. For example, I ...
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57 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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143 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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634 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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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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89 views

how to plot amplitude and phase of IMDs from their fft values?

i have my output as vector of 60000 complex number representing 10 sequence in frequency domain , each of length 6000. i need to plot the phase and amplitude of intermodulation distortion from this ...
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196 views

Analysing 3D image FFT

I'm looking for a way to visually inspect the amplitude of frequency components in a 3D image that I have taken the fftn of in matlab. Does anyone have any idea how to go about this?
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571 views

How to convert a sound file to any other data format which can be manipulated

I know this is very basic question and i am new to this site. But can anybody help me with my question. How to convert a sound file to other data format say using some type of transform (FFT or DFT) ...
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88 views

Keep the exact frequency content - Multidimensional fft

In Matlab I've got to generate a Gaussian process embodying a certain frequency content. Not to go multidimensional, I have used reshape function. I explain better ...
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356 views

What causes High Intensity Noise after Acoustic Echo Cancellation for a VoIP?

I am trying to implement a Acoustic Echo cancellation algorithm in Java for a VoIP system. This AEC will help to cancel the echo (coming from Speaker) in microphone input at the same PC. The sound ...
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0answers
206 views

Applying a filter kernel defined by a continuous equation in the frequency domain

I have a filter kernel $K(\omega)$ completely defined in the frequency domain as a continuous function of angular frequency $\omega$. I know $K(\omega)$ defined as a continuous mathematical equation. ...
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0answers
2k views

image registration using fft

I'm trying to register 2 images.First image don't change and second image is changing at each iteration by homography matrix and I'm using minimizer to find maximum of phase correlation, but for some ...
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679 views

Get bit stream from known radio frequency

I'm a beginner in radio demodulation, and several days can't solve my problem. The problem is to get bit stream from known frequency. I made I C# application that gets the data in real time from ...
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1answer
102 views

A few overview questions about FFT. Relationships between input, buffer size, and expected output?

I have a FFT set up and I've found that it responds very differently based on the buffer size and input. The output varies wildly, with magnitude of the peak frequency ranging from 500 to <1. I ...
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1answer
763 views

Signal amplitude to FFT amplitude

I am using Python to generate a sine wave in order to cancel out part of a signal I'm analyzing. I would like the magnitude of this signal in the FFT to be equal to the magnitude of the signal that I ...