Signaling took the form of a series of multifrequency (MF) tones, much like touch tone dialing between switches.
信号将一系列的方式多频(MF)音调，很像之间互动音频拨号开关。
2
The system includes the dual-tonemultifrequency signal detection module, the musical sound processing module, the harmonical analysis module of circularity and many other demonstration modules.