单音多频信号的产生和识别，采用FFT变换。应用于电话拨号。是学习数字信号处理的大作业。-Tone multi-frequency signal generation and recognition, the use of FFT transform. Applies to telephone dial-up. Digital Signal Processing is the study of large operations.

这是一个基于matlab的短时傅里叶变换时频分析工具箱2-This is a matlab-based short-time Fourier transform time-frequency analysis toolbox

双线性变换法设计Butterworth滤波器。分别画出滤波前和滤波后的时域图和频谱图。-Bilinear transform design Butterworth filter. Draw the pre-filter and the filtered time-domain and frequency spectrum.