Sentence:  The acuteness of sound in stringed instruments depends on three circumstances—length, thickness, and tension. The shorter, smaller, and tighter a string, the more <WSD>acute</WSD> the sound. ... In the violin, when you desire an <WSD>acute</WSD> sound, you tighten the string. When you wish a loud sound, you draw the bow over the strings heavily. 
Meaning of the word marked with <WSD> tags:  High or shrill.