说明：  数字电子琴的功能是基于数字信号发生器的，通过调用数字信号发生器产生一系列指定的频率的声音，从而达到虚拟的电子琴的功能，界面中包含1234567共7个琴键，鼠标按下时即发声，松开时发声停止。
(The function is based on the digital keyboard that is audible digital signal generator, digital signal generator generates by calling a series of specified sound frequency, so as to achieve a virtual keyboard functions, interface contains a total of 7 1234567 keys, mouse pressed , the sound stops when released.)