| 摘要 |
PURPOSE:To adjust sound volume automatically in accordance with noise level of surrounding even if the distance between a speaker and a microphone is closed, by detecting the surrounding noise with an input side audio signal. CONSTITUTION:The synthesized sound between the sound of a speaker 4 and surrounding noise is detected at a microphone 5 and inputted to a subtraction circuit 8 as a DC fluctuation output. On the other hand, the input audio signal of a sound volume adjusting circuit 2 is inputted to a signal level averaging circuit 11 as the DC fluctuation output and also to a level comparator 12. The average output of the signal level averaging circuit 11 is adjusted to a specified level at a level adjuster 13 and inputted to the level comparator 12. When the output level of a rectifying circuit 10 is a reference level or more, a storage circuit 15 holds this level. The output of the storage circuit 15 is subtracted from the referance level at a subtraction circuit 16 and inputted to an integral network 23. The integral network 23 makes high speed charging and low speed discharge. With the constitution like this, sound volume adjustment can be made automatically in accordance with the surrounding noise. |
