初级FFT系数与低通滤波器 [英] Primary FFT Coefficients vs Low-Pass Filter

问题描述

我正在处理信号处理问题.我正在提取一些功能以供分类器使用.在这些功能中，有前5个FFT系数之和.如您所知，初级FFT系数实际上指示信号的低频分量有多大.这与低通滤波器的效果非常接近.

I'm working on signal processing issues. I'm extracting some features for feeding a classifier. Among these features, there is the sum of first 5 FFT coefficients. As you know primary FFT coefficients actually indicate how dominant low frequency components of a signal are. This is very close to what a low-pass filter gives.

在这里，我怀疑计算FFT以获取前5个系数是否是不必要的任务.我认为应用低通滤波器只会消除低频分量，并且不会对主要FFT系数产生重大影响.但是，为了不使用FFT提取相同的信息(包含在前五个FFT系数中)，可能还有其他方法与低通滤波器结合使用.

Here I'm suspicious about whether computing FFT to take those first 5 coefficients is an unnecessary task. I think applying low-pass filter will just eliminate low-frequency components and it won't have a significant effect on primary FFT coefficients. However there may be some other way in combination with low-pass filter in order to extract same information (that is contained in first five FFT coefficients) without using FFT.

您对此问题有任何想法或建议吗?

Do you have any ideas or suggestions regarding this issue?

谢谢.

推荐答案

如果您只需要信号低频率部分的指标，我建议您做一些非常简单的事情.只需选择一个普通的低通滤波器，例如二阶巴特沃斯滤波器，并适当设置截止频率(如果您理解正确，则为5Hz).然后计算窗口上的能量(平方值的总和)或均方根值(长度100).或以低频率能量与窗户总能量之比来获得相对测量值.那应该为您的信号的低频贡献提供一个很好的指标.

If you just need an indicator for the low freq part of a signal I suggest to do something really simple. Just take an ordinary lowpass filter, for instance a 2nd order butterworth, with the cutoff frequency set appropriately (5Hz in your case, if I understood right). Then compute the energy (sum over squared values) or rms-value over your window (length 100). Or perhaps take the ratio of the low-freq energy and the overall energy of the window, to get a relative measure. That should give you a pretty good indicator for low frequency contributions of your signal.

人们倾向于过度使用fft来完成各种非常简单的任务.在90％的用例中，可以用更简单的算法替换fft.

People tend to overuse the fft for all kinds of really simple tasks. In 90% of the use cases an fft can be replaced by a simpler algorithm.

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