Of the Goertzel algorithm for the calculation of coefficients instead of 2 * cos [2 * pi * k / N], instead of using the 2 * cos [2 * pi * fn / fs], this can reduce the error.

• 对Goertzel算法的改进，对于系数的计算不是采用2*cos[2*pi*k/N]，而是采用2*cos[2*pi*fn/fs],这样能够降低误差。