| 摘要 |
In a telephone, a speech band switching circuit selectively provides a received speech with one of a plurality of frequency characteristics. A sensing circuit senses the level of noise around the telephone. A speech band control circuit compares the noise level sensed by the sensing circuit with a predetermined level and controls the speech band switching circuit on the basis of the result of comparison. When the noise level is higher than the predetermined level, the control circuit sends a control signal to the switching circuit. In response, the switching circuit selects a high-pass filter in place of a low-pass filter. As a result, a received speech is easy to hear despite the noise around the telephone because the low frequency range thereof is filtered out.
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