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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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8 views

OFDM modulator: Transmission time calculation

I have a problem with a certain task. The frequency of the signal sampling at the OFDM modulator output is 20 MHz. The length of the protection period is 2 microseconds and it is 20% of the ...
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20 views

When we compute doppler FFT, how can we find values corresponding to negative frequency?

I have a question. In case of FMCW radar processing, we compute 2stage FFT. The first FFT(range FFT) is used to find a distance between a radar and a target, The second FFT(doppler FFT) is used to ...
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2answers
69 views

why is my FFT magnitude of real time recording so volatile?

My goal is to do spectrum analysis of a gear motor. I used Python with the Pyaudio package and made a crude spectrum analyzer that displays the FFT as the sound is being recorded. I recorded 10 ...
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1answer
21 views

GCC-PHAT (Generalized cross correlation) always peak at delay=0 on real audio signal

I have studied the GCC-PHAT algorithm to estimate TDOA on audio signals at 2 mics. Here is my MATLAB implementation: ...
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1answer
26 views

Checking Parseval's Theorm for Gaussian signal by using Scipy

I'm trying to check Parseval's theorm for Gaussian signal. It's well known that fourier transform of $\exp(-t^2)$ is $\sqrt{\pi}\exp(-\pi^2 k^2)$. So I implement it by using quad and simps. I think ...
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1answer
28 views

Best way to resample an OFDM signal without interpolating + filtering?

I am working on a custom transceiver with a sampling rate of 3.84 MHz (256 OFDM subcarriers at 15 kHz, although 56 subcarriers are null). I would like to resample the signal to 5 MHz, in order to use ...
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39 views

Method for the Localisation of Impulsive Noise in Speech Signal

I'm sorry if this question has already been answered, but I couldn't find anything. I'm working on a program for noise detection and need to locate the position of impulsive noise. The following image ...
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25 views

retrieving complete 2d autocorrelation function from 2d power spectral density function (numpy.fft.ifft2)

My question is at the boundary between signal processing and python. I have a 2d power spectral density function (PSDF) constructed on Nx/2 + 1 and ...
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2answers
42k views

How to analyze audio input/spectrum correctly

I am quite new to Java and Signal Processing, but I was assigned a project dealing in audio processing. My topic given to me is a game that has a component of analyzing a song (any given song) and ...
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0answers
33 views

Equivalence of ML and FFT peak finding for Single-Tone estimation

My understanding is Maximum Likelihood and FFT peak finding for a single tone produce the same results assuming the ML is restricted to the same frequencies as the FFT. I was wondering if there was ...
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1answer
130 views

Wavelet transform and FFT using to extract feature power bands with EEG signals

I am using 5 channels [ fz , cz , c3 , c4 , pz] to detect drowsiness of driver My First Question is, what is the right input to get feature power band ( Theta , alpha , gamma , beta ) to wavelet ...
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308 views

Implementing Convolution with FFTW

UPDATE I've now implemented a timeshift on both the filter and the input signal, but this does not remove the noise. The plot below shows the original mono track in the upper panel. The middle panel ...
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1answer
144 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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2answers
143 views

How to seperate mixed signals, 3 identical gears meshing together

I have 3 identical gears that are meshing together, on each shaft that is holding these gears I have an accelerometer recording vibration data. Once I move to the frequency domain via MATLAB's ...
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1answer
45 views

Does dividing the magnitude spectrum of white noise by sqrt(2) give an RMS magnitude spectrum?

I understand that the RMS Amplitude of a sinusoidal signal is around 0.707 ($\frac1{\sqrt2}$) times the Peak Value, but this is not true for noise. However, an FFT of a noise signal indicates ...
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1answer
23 views

Clarification on the application of window pre-FFT

Good morning, I have a simple question about the application of a Hanning window before performing an FFT. My application is pretty textbook, i'm decoding a 4-FSK signal. Question: why does the ...
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1answer
31 views

DFT of a series of RC exponentials

Context: I'm trying use matlab to apply a single-pole filter to a time-domain ramp waveform that is generated by a sequence of time-shifted "RC steps" that are added together. The time domain voltage ...
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1answer
35 views

Why is the size of results from FFT half the size of the input, while that is not the case in image processing?

When dealing with real data, Fourier Transform produces symmetric results and FFT algorithms discards half of it. An input with 1024 points will yield only 513 points in the output. However, in image ...
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20 views

PSD Periodogram smaller segments compared to larger segment

I am calculating the power spectrum of a heart rate variability via FFT and a Welch window. I have a sample of 500 points as the input signal. The signal was broken up into two 128 point segments. ...
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1answer
69 views

Why is this recursive DFT algorithm not equivalent to this iterative method?

Edit 1/30 - Taking @Fat32's edits into account, it seems like there is still an issue with the scale of the frequency axis. While version 2 correctly identifies the response at 1 HZ, version 1 seems ...
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1answer
22 views

real time signal analysis of output from an audio device

I'm writing a test program that can detect pops/cracks/noise (unknown frequencies and duration) in the audio output of an audio device. The purpose of this program is to reduce human error and make ...
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0answers
21 views

Convolution in the Hartley Domain

The convolution Theorem of the Hartley Transform is given by $$ Y_{Ha}(k) = X_{Ha}(k)H_{Ha}^{e}(k) + X_{Ha}(-k)H_{Ha}^{o}(k) $$ where, $$ H_{Ha}^{e}(k) = \frac{H_{Ha}(k) + H_{Ha}(-k)}{2} $$ $$ H_{...
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31 views

Accelerometer signal processing

I'm new signal processing (this is my first pratical application), so I ask sorry if my question is simple. My challenge is to see the displacement of accelerometer when I have vibration too. I do ...
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1answer
50 views

Detrend data with no clear secular trend prior to Fourier analysis?

I am completing Fourier analysis on many different time series of sediment particle flux exiting an experimental flume. Data is collected at a resolution of 1 Hz for durations ranging from ~5,000 to ...
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1answer
53 views

Why do DFT frequency buckets need to be divided by sample period?

edit: This is my first post in this community. I'm sure that my downvoter had a good reason to do so, but could someone please comment and tell me how I can better format my question? -- I have a ...
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4answers
2k views

About Discrete Fourier Transform vs. Discrete Fourier Series

I am new to the field of signal processing. I am wondering what is the difference between DFS(Fourier Series) vs. DFT(Fourier Transform). For common applications, usually we get a segment(length <...
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48 views

Is discrete cosine transform differentiable?

Is DCT differentiable? I.e. is d(DCT(x))/dx defined? I've seen a few implementations in automatic differentiation software packages, so I suppose the answer is positive, but I'm still missing a ...
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1answer
69 views

Comparing multiple signals for similarity

I have multiple (between 2 and 100) signals and need to determine when a significant number diverge from the rest. We're exploring machine learning techniques, but we also want tackle this as a signal ...
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1answer
23 views

Quantized error in scatter plots for a hamming windowed LTE signal

I have a time domain signal based on LTE standards. Carrier spacing = 15KHz, Symbols per slot = 6, extended Cyclic Prefix = 512 samples FFT size = 2048, No. of sub carriers = 1200, channel BW = 20MHz, ...
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0answers
50 views

Sampling Frequency, Fast Fourier Transform and some strange results in python

So, I have 2 types of signals - Dirac: $\left[ 1,0,0,0,0..NumberOfSamples \right]$ and Gauss (it's sinus * window_gausian). I need to do some operation in ...
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5answers
6k views

Is there a technical term for this simple method of smoothing out a signal?

Firstly, I am new to DSP and have no real education in it, but I am developing an audio visualization program and I am representing an FFT array as vertical bars as in a typical frequency spectrum ...
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1answer
51 views

Threshold for peak detection of noisy signal in frequency domain

I have a noisy signal (Gaussian Noise) with a known SNR and known Noise variance. This signal contains a number of Frequency components. My ultimate objective is to detect the components of the signal....
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1answer
48 views

number of samples and Amplitude accuracy,what's the solution to this problem

I'm colleceting data samples from a device (temporal signal) in order to analyze it with FFT function in MATLAB R2015b,first i get N=4063 data points with (delta_t=0.000015s) so my frequency ...
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1answer
32 views

Failed to Get Silence in Audio Streaming

I want to detect silence in audio streaming. I've been following lot of answers from any website and i feel like know how to do that. but i doubt i'm on the right path coz the result doesn't seems ...
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0answers
24 views

Resources for learning Sound Processing [closed]

Does anyone know of any resources that explain simply, these are the data objects and variable definitions involved when doing sound processing? I took a class on image processing where we learned ...
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1answer
34 views

I have the scatter plots for a Hamm and Tukey(0.25) windowed data. The complex data plotted from Hamm windowed forms a pattern, why?

The Hamm windowed complex data forms some sort of a quantized pattern whereas in the same code if tukeywin(0.25) is applied normal noise is observed. Any idea why ?
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1answer
194 views

Decimation and filtering in the frequency domain

I'm working on a Software Defined Radio project where I'd like to low-pass filter and decimate an analytical signal (IQ) sampled at 96ksps. Let's say the low-pass filter has a cutoff at 5kHz and I'd ...
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1answer
63 views

Autocorrelation: numpy versus FFT

I have a series a of values (0 and 1) coming from a Brownian process with drift for which I am studying the autocorrelation. I used two methods: 1) numpy autocorrelation: ...
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0answers
26 views

FMCW radar 3D FFT for DOA estimation

I'm dealing with transformation of coordinates after I do the 3d FFT doa estimation. Data below is a car in front of the radar board, and the angle of arrival is "0", 50m. Left image is the row has ...
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1answer
24 views

How to custom optimize cuFFT for a mini batch of multi-channel images?

I am reading a paper, which has the following paragraph. Current GPU implementations of the FFT such as cuFFT are designed to parallelize over individual transforms. This can be useful for ...
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2answers
856 views

Phase Correlation and Negative Shifts

I am implementing phase correlation algorithm to determine shift between two images. It generally works, but I am not sure how to interpret the resulting shift. Pseudocode: ...
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0answers
18 views

Is it customary to use the period as coefficient when sampling the impulse response?

I have an analog, continuous impulse response $$h_a(t)=u(t)\cdot\sum_{n=1}^4A_ne^{s_nt}$$, and by sampling it with the usual method I get $$h[n]=\Delta th_a(n\Delta t).$$ Now, that $\Delta t$ is a bit ...
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2answers
570 views

how were DTMF frequencies determined exactly and how can I extend them?

I've been playing with DTMF frequencies and the Goertzel algorithm, and would like to know exactly HOW the DTMF frequencies were determined. I understand that they were chosen such that none of the ...
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1answer
29 views

Irregularities in tone generated using FFT data

I am implementing a simple program to generate tone in MATLAB using FFT/iFFT by zeroing all frequency bins except for the one frequency that I'd like to generate a tone in. Sampling frequency is ...
3
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1answer
2k views

Implementing Frequency Domain Convolution in MATLAB (Convolution Theorem)

I'm trying to prove convolution in time domain is same as multiplication in frequency domain but I'm not getting the same answer in matlab. Here is the code:
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1answer
16 views

performing FFT on Voltage measurments to get Z(f)

I have a csv file containing measurments a system's step response when the step is current and the output is the voltage. output looks something like this and the it's evenly sampled provided I know ...
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1answer
39 views

Performing DFT twice on an image. Why am I getting an inverted image? [duplicate]

I was asked to perform DFT on an image twice as a part of my school assignment. Why am I getting a blurry inverted image when I perform DFT on an image twice? Sorry, I'm new to image processing and ...
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1answer
40 views

Autocorrelation sequence in terms of Fourier transform of the underlying signal

Let $x(n)$ be a sequence of length $N$, which is zero outside the interval $(0,N-1)$. Let $X(k), k=0,1,\cdots,N-1$ be the FFT coefficients of $x(n)$, that is, $X(k)=\sum_{n=0}^{N-1}x(n) \exp\left( -\...
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2answers
83 views

How to increase resolution of FFT?

I have an input signal in the ( 0 - 20 kHz ) frequency range . When i sample this signal maximum sampling frequency is around 40 kHz . When i calculate the FFT using 1024 points i got resolution of ...
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1answer
36 views

Linear Chirp parameters from a segment of the signal

Edit:" please see the attached figure. The blue part is all I have. Also, you can neglect the noise term. Assume the signal is deterministic. Typical values of the unknown parameters $\alpha$ and $\...