管弦乐队在定弦。

The orchestra are tuning up.

这和小提琴中间两根弦的定弦是相同的。

This is the same as the two middle strings of the violin.

他将丝弦改为钢弦丝，同时把定弦提高了。

He changed the silk strings to steel ones, and raised the tones.

当调校弦乐器（定弦）时，应每秒弹拨一次，以保持音符“清新”。

Pluck the instrument once per second to keep the note 'fresh' while you are tuning.

渐开线锥形齿轮由于同时存在锥度和螺旋角，使得其固定弦齿厚无法精确测量，也没有公法线。

There is no common normal in the conical involute gear and the fixed chordal tooth thickness can not be measured accurately because of the coexistence of helix angle and taper.