separate signal path for on air and PA

• 二级调音

separate signal path for on air and PA的用法和样例：

例句

1. I asked him to tune my violin for me.
   我请他为我的小提琴调音。
2. The experienced drummer should know the sweet spot for the tuning.
   有经验的鼓手会知道对于调音来说最佳的听音位置。