| 摘要 |
PURPOSE:To obtain an echo without any distortion deterioration by an AD converter or DA converter by mixing an input signal and a feedback signal in a digital signal state. CONSTITUTION:When an up switch 12 is turned ON and a coefficient ROM 10 is stored with the pattern of an echo feedback quantity which increases monotoneously, an up/down counter 11 counts up with the clock from a clock generator 20 and when the counter stops counting up at Ta, an address of the coefficient ROM 10 is selected with the counted value, so that a constant coefficient is selected. A multiplier 9 multiplies the coefficient by a digital signal outputted by a RAM 6 to obtain the feedback digital signal Ve. Then a digital adder 4 adds the feedback digital signal Ve and the input digital signal from the AD converter 3 and the sum is written in the RAM 6 and read out of the RAM 6 a constant time t1 later to obtain a necessary echo signal pattern. Consequently, the echo is obtained without any distortion deterioration by the AD converter nor DA converter. |
