| 摘要 |
PURPOSE:To reduce the signal level of noise from the external by variable setting the transfer function, namely, the gain of an amplifying circuit to a specific range with respect to the transfer function of a headphone unit, that of a microphone unit, and that of a feedback circuit. CONSTITUTION:The synthesized output signal from a signal synthesizer 2 is supplied to a headphone unit 4 through a variable gain amplifying circuit 3 whose gain A is freely variably set, and a noise signal N from the external is added to this acoustic output signal by a signal adder 15. This synthesized output is converted to an electric signal as the acoustic signal around the unit 4 by a microphone unit 6 and is supplied to the signal synthesizer 2 through a feedback circuit 7. In this headphone device, the transfer function, namely, the gain A of the amplifying circuit 13, a transfer function H of the unit 4, a transfer function M of the unit 6, and a transfer function beta of the feedback circuit 7 are variably set in the range of ¦AHMbeta¦>>1. Thus, a practical active noise reduction headphone is obtained. |
