| 摘要 |
A reception volume limiting circuit includes a detecting section, an A/D conversion section, a control section, and a speech data calculating section. The detecting section performs detection/rectification and smoothing of a receiver driving AC signal and outputs a DC signal corresponding to the level of the receiver driving AC signal. The A/D conversion section converts the DC signal into a digital signal. The control section calculates a time average value by averaging the digital signal every predetermined time interval, adds the currently stored attenuation amount to the time average value, and compares the time average value with a predetermined threshold value representing a critical sound pressure for protection of listener's hearing. If the time average value exceeds the threshold value, the control section calculates an excess level from the difference between the two values, stores the excess level as a current attenuation amount, and outputs a volume attenuation command having the excess level as an attenuation amount. The speech data calculating section performs subtraction processing of the reception speech data, in response to the volume attenuation command, on the basis of the excess level included in the command and outputs reception speech data attenuated by a value corresponding to the excess level. |
