音 is a versatile noun covering 'sound' in general (both natural and musical), especially when it forms part of a compound (音乐 'music', 声音 'sound', 噪音 'noise'). It also carries a literary meaning of 'news' or 'message' (佳音 'good news'), and in specialized contexts refers to linguistic units (音节 'syllable', 音素 'phoneme'). Unlike the broader 声音, 音 leans slightly toward the abstract or tonal aspect of sound. You'll rarely hear it alone as a standalone word in everyday speech; it almost always combines with another character.