It is sometimes mistaken for a power supply hum. 有时候，亚音频会被错误的认为是电源交流声。
All that is needed is a power source. 全部工作所需要的只是一个动力源。
That part of a flight, in which the paraglider is not towed, carried or assisted by another aircraft or separate external or jettisonable power source. 飞行伞没有被拖曳，运载或经由另一个航空器或独立的外部或可抛弃式动力源的协助，所作的飞行部分。
