Twenty feet -- that's six meters. Other suggestions include putting more distance between you and the device and using good lighting.

VOA: special.2011.08.01

What string technique are the violins using at this particular moment and then what rhythmic device does the trumpet insert?

在这个特殊的瞬间,小提琴用到了什么演奏技术,之后小号又用了什么节奏方法

耶鲁公开课 - 聆听音乐课程节选

What string technique are the violins using at this particular moment and then what rhythmic device does the trumpet insert?

在这个特殊的瞬间,小提琴用到了什么演奏技术,之后小号又用了什么节奏方法

耶鲁公开课 - 聆听音乐课程节选