| 摘要 |
PURPOSE:To attain stable high noise eliminating performance by providing a bypass equivalent circuit in parallel with a noise eliminating speaker and a monitor microphone and using a subtraction circuit so as to subtract one of two signals being an input signal from the monitor microphone and a bypass signal from the bypass equivalent circuit from the other. CONSTITUTION:A cancel tone generating signal F outputted from a noise cancel circuit 3 is inputted to a parallel bypass equivalent circuit 4. The bypass equivalent circuit 4 gives a signal change equivalent to a signal change (phase lag and gain change) when the cancel tone generating signal reaches a preamplifier 3a from a branch point G via a noise eliminating speaker 1 and the monitor microphone 2 to form a bypass signal H. Thus, when a subtraction circuit 3b subtracts the bypass signal H from the bypass equivalent circuit 4 from the input signal D from the monitor microphone 2, since the component of the cancel tone A included in the input signal D is equivalent to the bypass tone signal H, the component is eliminated completely by the subtraction to prevent production of howling. |
