power-line hum 动力线哼声
The purpose of a balanced line is to transfer a "signal" from one place to another while rejecting "ground noise", which is not white noise or hiss, but power line related hum and buzz.
平衡传输线，是将信号从一个地方传到另一个地方的同时抑制“接地噪声”。
Line frequency hum, primarily induced by imbalance in the filament circuit wiring, the transformer used to power the filament, coupling into the signal leads, etc.
市电频率Hum， 主要原因包括灯丝线路走线导致的不平衡；供给灯丝的电源变压器（缺陷）导致电源杂波耦合进入信号通道，等等。
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