Function 7     : Input Voice.

Entry          : BX = 7.
                 AX = Sampling rate (4000 - 12000 in Hz).
                 CX = Length of input buffer.
                 DI = Address of input buffer.
Exit           : None.

This function uses DMA to input digitized sound. The program
flow is also returned to the calling program immediately with
0FFFFH stored in the status word.

The voice input ends when the input buffer is full or it is
terminated by the "Stop Voice Process" function. When either of
there conditions happens, the status word is set to zero.