noun
musical tuning
Refers to the act of tuning musical instruments or adjusting sound to the correct pitch.
演奏の前に音合わせをしましょう。
Let's tune up before the performance.
調律 is a more formal term for tuning, especially for pianos and other fixed-pitch instruments, while 音合わせ is a general term for matching pitches.
Compound of 音 (おと, 'sound') and 合わせ (あわせ, 'matching'), from the verb 合わせる (あわせる, 'to match').