If this parameter is NULL, any currently playing waveform sound is stopped.

也就是第一个参数设置为NULL，就可以停止播放了。

youdao

This added resistance causes the waveform frequency to drop, lowering the pitch of the sound you hear internally and creating a sort of feedback effect that stimulates the eardrum from both sides.

声波降调的可能性增加，并且随着鼓膜双次振动带来的反馈效应，音高也会随之降低。

youdao

SoundCloud allows us to embed those sound files right on WhiteHouse.gov, and users on SoundCloud can leave time-specific comments right in the waveform (the visual representation of the sound file).

WHITEHOUSE: Hearing from the White House in a New Way