说明：  DTMF(双音多频)是用两个特定的单音频组合信号来代表数字信号的一种编码技术。两个单音的频率不同，代表的数字或实现的功能也不同。可采用8种频率代表电话机上的16个按键，10个数字键0~9和6个功能键*、#、A、B、C、D。具体的频率组合见参考书。要求： (1) 根据键盘输入的符号，利用MATLAB产生对应的DTMF信号；(2) 分别利用FFT算法和Goertzel算法计算该DTMF信号的频谱并画出频谱图；(3) 根据频谱图确定DTMF信号所代表的符号是否和输入的符号一致。
(DTMF (Dual Tone Multi-Frequency) is a single with two specific combination of audio signals to represent a kind of digital signal coding techniques. Two monosyllabic different frequency, on behalf of the numbers, or the realization of the functions are also different. Eight kinds of frequency of use on behalf of telephone on the 16 keys, 10 numeric keys 0 ~ 9 and 6 function keys*,#, A, B, C, D. The frequency of specific composition of reference books. Requirements: (1) According to the keyboard input of symbols, the use of MATLAB have a corresponding DTMF signal (2), respectively, using FFT algorithm and the Goertzel algorithm DTMF signal spectrum and frequency spectrum draw (3) According to DTMF signal frequency spectrum to determine represented by symbols and input symbols unanimously.)