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.

FFT的详细原理分析，且基于DSP处理器的详细C实现算法。值得学习。-Detailed schematic of the FFT analysis, and algorithm based on DSP processor C. Worth learning.