BTestimate_hz

代码说明：

  在现代谱估计中，用自相关的无偏估计代替周期图中自相关函数的有偏估计，可能导致出现负的谱估计值，因此采用BT谱估计器的方法(In the modern spectral estimation, the use of self-related unbiased estimate the figure to replace the cycle of auto-correlation function biased estimate may lead to a negative estimated value of the spectrum, so the use of BT s method of spectral estimation)