双音频按键识别

背景：

打电话拨号时，每次按键会发出不同的声音，这些声音实际上是由一些固定频率的正弦信号合成的。因为每个按键声音包含两个不同频率的正弦信号，因此也被称为“双音频”信号，简记为DTMF。这相当于是对不同键位用‘音频’进行了编码，如同计算机领域中用数字0和1对处理对象（包括键盘）进行编码。-Two-tone buttons identify Background: When you call dial, each key emits different sounds, which is actually made up of some fixed frequency sinusoidal signal synthesis. Because the sound of each key contains two sinusoidal signals of different frequencies, it is also known as " two-tone"　signal, abbreviated as DTMF. This is equivalent to different keys using the ' audio'　encoded, as the computer industry with the numbers 0 and 1 pair of processing object (including the keyboard) to be encoded.