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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Problems computing the DFT of finite length sequence

I am having trouble finding the same answer as the solution manual for this sequence. The problem asks to compute the DFT of $x[n]=$${1,\ \ \ even\ 0 \leq n \leq N-1}\brace{0, \ \ \ \ odd\ \ 0 \...
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27 views

ADC full scale range problems

I have a simulated ADC in Matlab with a Full-Scale-Range of 2V. I calculated some performance parameters (SINAD, SFDR, THD, ENOB) for a sinusoidal input signal with an amplitude of 1V, such that the ...
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642 views

Zero Padding in Frequency Domain (Spectrum): How to Split the Middle Bin (Nyquist Frequency)?

When a complex digital signal is converted to its spectrum through an FFT, the result will contain a series op positive and negative frequencies. That is, when the spectrum has N bins. Bin 0 will be ...
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128 views

In the context of DFT, Where Does the Nyquist Frequency Sample Belong In a Double Sided Frequency Spectrum (Positive / Negative Side)?

If we have an even number of data points $N$, after DFT in MATLAB, the output has the order: $$(\text{DC}, f_1, f_2, \ldots, f_{N/2-1}, f_\text{Nyq}, -f_{N/2-1}, -f_{N/2-2}, \ldots, -f_1)$$ For real ...
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616 views

Power spectrum RMS or peak

I’m a newbie and wondering if I calculate the power spectrum from the peak amplitude or from the amplitude rms ? This is my matlab script so far: ...
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1answer
4k views

How many multiplications and additions does it take to compute an FFT of a signal?

How many multiplications/additions does it take to execute an FFT operation in terms of the length of the signal $N$ and the number of FFT bins $M$? I don't want an answer in terms of big O, but ...
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1answer
32 views

Should we divide the power at 0Hz by two for Single-Sided Power Spectrum with FFT?

To make my question as clear as possible I will go through an example. I want to plot one sided power spectrum of a signal. As an example my signal is sum of "50Hz sine with and amplitude of 1V&...
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1answer
38 views

Meaning of the frequencies vector using fft

I'm so confused, and it would be nice if someone could clear my head, or at least direct me to suitable references. Assume that I have two gaussian pulses with the same bandwidth in time, but for 2 ...
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1answer
53 views

Why do the DTFT and FFT give me completely different results for magnitude at a specific frequency?

I am trying to write a program to compute the magnitude and phase of a specific, non-integer frequency component (i.e. given a sampled finite signal of length $N$, I want to know the magnitude and ...
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207 views

Interpreting N in DFT as the Number of Points vs. Number of Intervals

The "N" is DFT is understood to be the number of data points in a given sequence or in other words the length of the sequence. We recently have had discussions here Indexing in DFT (from an ...
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2k views

Definition of the DFT / FFT Bin Size

When reconstructing the frequency domain for an FFT, what is the most self-consistent way to do this -- i.e. how is it best to define the bin width, $\Delta f$? For example, previously I thought it a ...
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99 views

Why Is the Total Time Equal to $ N \cdot {T}_{s} $ and Not $ \left( N - 1 \right) \cdot {T}_{s} $ In the Context of DFT?

In the definitions of the DFT DFT $$ X(j)=\sum_{k=0}^{N-1} x(k) \exp \left(-i 2 \pi\left(\frac{j}{N}\right) k\right) $$ Let us say, if we have $10$ points, $N=10$, each sampled at $0.2$ seconds, why ...
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1k views

Sinc Interpolation Using DFT (FFT)

Lets say I want to double the number of points in an array f. I had the idea to do this: F=fft(f);N=length(f); FF=[F(1:N/2) zeros(1,N) F(N/2+1:N)]; f=ifft(FF); ...
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The best method to convert piano sound to music notes in real time [duplicate]

I was looking for a way to convert piano sounds to piano notes for my research. I discovered the conversion of piano sound to piano notes using FFT and piano note recognition using CQT. I am also a ...
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Possibilities in Audio Convolution Math

New Python user here! I am a musician working on a program to streamline a process of using convolution math on a folder of .wav samples. The idea is that each audio sample will be multiplied with ...
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The effect of time increment $\Delta t$, frequency resolution $\Delta f$ and Gibbs phenomenon on the amplitude of the signal in the frequency domain?

Experiment: Vibration analysis (i.e.: major concern is on transfer function or frequency response). The input is an impulse (imagine as a knocking effect or knocking force), defined as a half sine ...
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4answers
1k views

How do I calculate peak amplitude of the signal components after zero padding and FFT?

I am learning about DFT and trying to apply it to some audio processing. I am new to DSP but experienced in programming and have some background in math and physics. The FFT algorithm I use (lomontFFT)...
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2answers
120 views

Where is the Nyquist frequency in an FFT spectrum?

I've been working with even length audio for a while, so I've had no problem finding the Nyquist frequency in the FFT spectrum, as it's shape is: $$(\text{dc_component}, f_1, f_2, ..., f_{N/2-1}, f_\...
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1answer
36 views

I need help interpreting FFT diagram

I need help with analyzing the computed FFT of my signal. I don't wanna bother by going into the details of how my signal is formed so I will just state which frequencies I know my signal has. I know ...
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1answer
95 views

How to achieve a smoothed frequency phase response with no outliers

I have two sampled signals, which I then perform wavelet analysis on, by synthesising the Filterbank, perform the dft on each kernel, and the dft on the sampled signals, and multiply together. ...
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Properly stagger an FFT? How to handle output data (Have highs weigh as much as lows?)

I'm new to audio processing so I'm mostly running into problems with not being able to properly google something. Sorry. Basically I want to create something like an equalizer (just visually without ...
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1answer
41 views

Meaning of lines on x- and y-axis of a centered FFT-spectrum of an image

I am currently learning about the Fourier transform of digital images, but I am wondering about one aspect. In most visualisations of fourier transforms of images, a horizontal and a vertical line in ...
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1answer
267 views

Matlab: Different 1-D FFT results with and without zero-padded

Recently I am implementing FFT with C code. So I use Matlab for algorithm verification. As Radix-2 FFT was chosen, I've learned that zero-padding technique could help to reach 2^N limitation without ...
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2answers
76 views

Difference between $\tt fft$ and $\tt dftmtx$ in MATLAB

I have the following MATLAB code: ...
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1answer
48 views

The effects of frequency resolution in FFT on the frequency spectrum

This is a section for the parameter study of my thesis (basically: why and how I did what I did in the experiments). Currently, I have to choose the fit bandwidth and FFT lines combination for the ...
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68 views

Calculate periodicity of audio signal

I have to calculate the periodicity of a audio signal like this: You can see by eye, that the volume rises the highest every second "blob". The spectogram (that is visualized ...
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1answer
73 views

Frequency from mic Raspberry Pi

I am working on C++ project based on Raspberry Pi. I have to make program that recognize siren of emergency vehicle(sound capture by microphone). I made a huge internet research and stopped with small ...
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2answers
8k views

How can I decide proper FFT length(size)?

I'm trying to understand about deciding FFT length(size) and relative factors. what If I got the streaming adc data as the below, ...
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2answers
94 views

Non-zero DFT components where zero is expected?

I am implementing DFT in Octave. Here's my code: ...
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1answer
193 views

FFT filter to remove cd scratch

I have a .wav file which came off of a cd with a scratch, so there is a periodic "clicking" of about 6 Hz. I was playing around with trying to squash the clicking by taking FFT and filtering the ...
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1answer
35 views

Where 2-D DFT is necessary in image processing applications instead of 2-D DCT?

As we know the 2-D DCT is a real-valued kernel and less computational complexity and it used in several image processing applications like image compression etc. 2-D DFT is a complex kernel and high ...
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3answers
937 views

Distribution of energy in frequency bands

On my wav-file (music), I do a short-time Fourier transform (STFT). I have spectrum, which spans from $0\textrm{ Hz}$ to $f_s/2$. I took out the range between $1$ and $1000\textrm{ Hz}$, which I ...
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3D data centering before fast fourier transform

I am using fftw to conduct a 3 dimensional fft and then apply a guassian filter. In order to shift the frequency, I need to first rotate the data matrix before fft. In 2D, I know how to do it, e.g., ...
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1answer
49 views

Do i need to remove mean in STFT when working on music audio?

i need to apply a STFT to some music audio files but i can't understand if i should remove the mean or not. I know that for stochastic signals that is a must and that sometimes also necessary for ...
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289 views

(I)FFT without Bit Reversal

It's been a long time since I scratch built an FFT algorithm, and I feel like I should already know this, but I just can't recall and figured I might get a quick answer on here that may be useful to ...
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Why the inverse discrete fourier transform of the Ricker pulse isn't the same as the Ricker pulse in time domain?

Question I'm trying to use Python's scipy library to compute the IDFT of the Ricker wavelet function and compare it with the analytical time-domain version of the same function. When I compare the ...
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2answers
708 views

Curved noise floor and ugly unexplained peaks after FFT

It has been so long since I studied this at University, so I'll better ask here if I'm doing something really wrong here. I'm using a USRP frontend for L1 band surveillance. I want a 20MHz bandwidth, ...
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1answer
79 views

Serial filtering using FFT

lets say I have 3 audio filters for a realtime DSP application. For simplictity each has length 256 (as well as the input signal). The filters should work in series. Starting with filter IR h1(n) and ...
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1answer
190 views

Question about FMCW range-velocity plot

I am working on plotting range-velocity heatmap of the receiving FMCW signal. I actually have already plotted. However, I do not really understand the mapping relationship between Doppler FFT bin and ...
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2answers
176 views

Higher-order Kronecker product

I am trying to generate a 2D DFT matrix in matlab, which I need for 2D compressed sensing (CS) problems. Lets say $N_1=8$, $N_2=16$, then according to the requirement of CS, to generate a 2D DFT ...
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2answers
54 views

Comparing two small audio files (e.g., hand clap) Android

Dears, I am new in signal processing and I am dealing with an Android application that should do some audio files (having the same "small" duration) comparison in real time. My main focus is ...
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2answers
82 views

Inaccurate phase returned by np.angle

I am generating 2 sine waves, first one has fundamental frequency = 50 Hz, amplitude=10, phase=0, the second one has fundamental frequency = 100 Hz, amplitude = 5 and phase = np.pi/6 (which is ...
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10 views

How to get the phase/angle from an Alglib complex variable

It is easy to get the magnitude using alglib.abscomplex function (https://radfiz.org.ua/files/temp/Lab1_16/alglib-3.4.0.csharp/csharp/manual.csharp.html#gs_stdfunctions), but I would like to know, how ...
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1answer
44 views

Is there a way to break down a signal into its respective phases (4 in this case) to be later analysed individually

Is there a way to extract amplitude information but over 4 phases of the same frequency. That is, if the frequency is known could I extract amplitude peaks (between given values)in the time domain in ...
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1answer
52 views

Coherent averaging of polyphase components of a signal

I want to subsample a multi-band signal to introduce controlled aliasing. My frequency components are uniformly distributed across the spectrum (comb structure) and occupy a relatively narrow ...
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1answer
35 views

Strange behavior from frequency to angular frequency in FFT

I have written a code to compute the Fast Fourier Transform of a simple complex exponential with frequency $f=50.0$, using scipy.fft. The code is written below: ...
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1answer
24 views

Swift vDSP rFFT not same as Python np.fft.rfft()

I am trying to implement real FFT in iOS, for that i am using Accelerate Framework. Here is my Code for Swift. ...
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2answers
428 views

Matching LPC frequency response to raw sample data frequency response

Background: The intention is feature/formant extraction from speech input. I have used an FFT on raw samples in the past and have done simple peak picking from a weighted average of frequencies over ...
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51 views

How to conduct spectrum analysis on a wav audio file using SciLab?

I am working on a wav audio file using SciLab. The wav file is to undergo the FFT (Fast Fourier Transform) by using the fft function to obtain the spectrum analysis ...
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43 views

Forecasting that FFT result

I have the following FFT result charts. Searching for a way to forecast the future AMPLITUDE steps from the Time Domain Plot if possible, or the next maximum/minimum deviation based on some previous ...

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