| 摘要 |
A gated oscillator is coupled to a set of headphones through a connector interposed between the headphone plug and a mating jack in a stereo receiver or other source of audio information. An acoustic pickup is coupled to the oscillator through circuitry which establishes a threshold for the oscillator. When a sound sufficiently loud to exceed a threshold is detected by the pickup, the oscillator is actuated and superimposes an audible tone on the audio information.
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