fft

【多项式】FFT

由 |▌冷眼眸甩不掉的悲伤 提交于 2019-12-25 03:55:13
【多项式】FFT Preface 本文对所有 \(\LaTeX\) 编译后生成的文本共有大约 \(7000\) 字，其中前半部分为前置知识部分，介绍了多项式的有关概念、运算法则以及复数的概念、运算法则以及单位根有关内容，并证明了蝴蝶操作所用到的有关复数的两个重要引理公式。如果你对上述内容已经有了解，可以跳过 Pre-knowledge 部分。 Pre-knowledge 部分大约有 \(2000\) 字。 由于内容比较长，本文还没有经审阅人完全审阅完成，如果您发现了文本中的错误，请私信或评论我指出。 Pre-knowledge 多项式 Definition 称一个关于 \(x\) 的式子 \[f(x) = \sum_{i = 0}^{n} a_i \times x^i\] 为一个 \(n\) 次多项式，其中 \(a_i\) 为常数。称 \(n\) 为 \(f(x)\) 的次数。显然， \(f(x)\) 可以看做一个关于 \(x\) 的 \(n\) 次函数 \(y = f(x)\) 。 回忆初中解析几何最后一个大题的第一问，正常情况下都是给定三个点的坐标，求一个关于 \(x\) 的二次曲线解析式方程。而类似的如果求一条直线的解析式，则需要给出两个点的坐标。 类似的，对于如果想要确定一个 \(n\) 次函数的解析式，则需要 \(n + 1\) 个点的坐标。这是因为一个 \(n\)

Template Matching using FFT

由 谁说我不能喝 提交于 2019-12-25 03:50:11
问题 Can anyone please explain how to perform template matching using FFT. The template is smaller than the original image. 1. Everywhere it states that the template has to be padded with zeros. How it is done. Is it added to the bottom and right of the image or equally around the entire image. Thanks in advance. 回答1: You are using the Fourier Transform to calculate the cross correlation; it's as simple as that. Padding is performed around all sides of the template. This is because a standard Fast

Can someone explain what the output of fft means in MATLAB?

由 ≡放荡痞女 提交于 2019-12-25 03:44:34
问题 >> fft([1 4 66]) ans = 71.0000 -34.0000 +53.6936i -34.0000 -53.6936i Can someone explain according the result above? 回答1: EDIT Well that's embarassing. I left out a factor of 2. Updated answer follows... The Discrete Fourier Transform, which an FFT algorithm computes quickly, assumes the input data of length N is one period of a periodic signal. The period is 2*pi rad . The frequency of the output points is given by 2*n*pi/N rad/sec , where n is the index from 0 to N-1 . For your example,

Recognize sound based on recorded library of sounds

由 谁都会走 提交于 2019-12-25 02:57:11
问题 I am trying to create an iOS app that will perform an action when it detects a clapping sound. Things I've tried: 1) My first approach was to simply measure the overall power using an AVAudioRecorder. This worked OK but it could get set off by talking too loud, other noises, etc so I decided to take a different approach. 2) I then implemented some code that uses a FFT to get the frequency and magnitude of the live streaming audio from the microphone. I found that the clap spike generally

implementing FftPitchDetector in C#

由 爷，独闯天下 提交于 2019-12-25 02:39:05
问题 I've added FftPitchDetector.cs into my project, but I'm not sure how to use it. My code: private void sourceStream_DataAvailable(object sender, NAudio.Wave.WaveInEventArgs e) { if (waveWriter == null) return; byte[] buffer = e.Buffer; float sample32 = 0; int bytesRecorded = e.BytesRecorded; float[] floats = new float[buffer.Length]; waveWriter.Write(buffer, 0, bytesRecorded); for (int index = 0; index < e.BytesRecorded; index += 2) { short sample = (short)((buffer[index + 1] << 8) | buffer

By reversing the polarity of a time domain signal, can I cancel the source audio?

由 拜拜、爱过 提交于 2019-12-25 00:22:00
问题 I have an input signal in time domain (that is, discrete 14100 signed integers per second). If I reverse the polarity (signed-ness) of each value, will I not produce a destructive source-audio canceling signal? 回答1: Destructive cancellation by simply reversing polarity will occur only if your total software/hardware/system/transducer delay time from your input signal to to your output signal to the point of cancellation is zero (or a very tiny percentage of the period of the highest frequency

Unable to use CMSIS library in Atollic

由 空扰寡人 提交于 2019-12-24 22:15:31
问题 I am trying to use CFFT function for my STM32 microcontroller in Atollic TrueStudio. But I am unable to use any of the DSP functions. I get the error - undefined reference to `arm_cfft_f32' and undefined reference to 'arm_cfft_sR_f32_len16'. I don't know what the problem is because it works on Keil. What am I doing wrong? #include "stm32f4xx.h" #include "arm_math.h" #include "arm_const_structs.h" #include "core_cm4.h" #include "math.h" #define TEST_LENGTH_SAMPLES 32 float32_t ffttestip[TEST

Correct frequency axis using FFT

由 寵の児 提交于 2019-12-24 18:19:23
问题 How can I get the correct frequency vector to plot using the FFT of MATLAB ? My problem: N = 64; n = 0:N-1; phi1 = 2*(rand-0.5)*pi; omega1 = pi/6; phi2 = 2*(rand-0.5)*pi; omega2 = 5*pi/6; w = randn(1,N); % noise x = 2*exp(1i*(n*omega1+phi1))+4*sin(n*omega2+phi2); h = rectwin(N).'; x = x.*h; X = abs(fft(x)); Normally I'd do this : f = f = Fs/Nsamples*(0:Nsamples/2-1); % Prepare freq data for plot The problem is this time I do not have a Fs (sample frequency). How can I do it correctly in this

How does Octave spectrogram 'specgram' from signal work?

由 只愿长相守 提交于 2019-12-24 17:39:27
问题 I'm trying to test the specgram function located in the signal package in Octave but I'm a little confused at the input/output variables for specgram. What I would like to do is be able to get the specgram data into an array that will show the frequency and the length of time when the frequency starts and stops. See example code below: I was trying to get the array to show that for the length of t1 it will be 7hz, t2 will be 12hz and for t3 will be 2hz. How can I go about doing this? I'm

How to create the complex representation from magnitude and phase information to perform an inverse fast fourier transform(IFFT)? [duplicate]

由 心已入冬 提交于 2019-12-24 16:33:18
问题 This question already has an answer here : FFT Images and its Inverse (1 answer) Closed 4 years ago . I have a problem with converting amplitude and phase data into the complex form, which is required to perform an IFFT. (inverse fast fourier transform). This is the only data I have. My frequency range goes from 0.1 to 2.6 and, with 200 samples. I would like to use IFFT to obtain a time signal. How do I convert this magnitude and phase dataset into the complex plane? I have never used IFFT
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