耳机接口这种模拟连接原本是20世纪初专为老式电话交换机所设计的。

Thee headphone jack is an analog connection originally designed for old-fashioned telephone switchboards in the early 20th century.

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在70年代早期，大多数电话交换机还是机电模拟转换器。

In the early 1970s, the majority of telephone exchanges were still electromechanical analog switches.

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在70年代早期，大多数电话交换机还是机电模拟转换器。

In the early 1970s, the majority of telephone exchanges were still electromechanical analog switches.

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