| 摘要 |
PURPOSE:To reduce low frequency noises without varying its sound quality by varying a low frequency component level when the output of a high-pass filter means becomes larger than the output of a low-pass filter means, and allowing the low-pass filter means to whether or not there is a low frequency signal with an enough level to mask low-frequency noises sufficiently. CONSTITUTION:A playback audio signal is supplied to a high-pass filter circuit 5, which extract high frequency signal which easily generates a low frequency noise. Consequently, the low frequency noise which can not be measured directly is detected indirectly. When the output of the high-pass filter circuit 5 is larger than the output of the low-pass filter circuit 2, a low frequency noise is easy to generate, there is no signal which masks the low frequency noise, and even when the gain of the low frequency signal is lowered, there is no large variation in sound quality. Further, when the playback audio signal has a spectrum which easily generates a low frequency noise and there is no signal component masking it, frequency characteristics of a variable filter circuit 4 are varied to lower the low frequency range. |
