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Intonation, in music, is a player's realization of pitch accuracy.

In string instruments, intonation is more of a worry than in other instruments. Because many string instruments are unfretted, if a finger is too high or too low by even a fraction of a centimetre, the note will be out of tune. The process of gaining good intonation typically takes many years of playing to acquire and is arguably the hardest part of learning a stringed instrument.

The same principles of intonation that apply to strings apply to the trombone, because the trombone uses a slide instead of valves. However, the margin of error is much wider on the trombone as it has only seven basic slide positions on a slide length of over 80 centimetres.

Instruments with straight frets such as guitars require special compensation on the saddle and nut. Every time a string is fretted, it is also stretched. As the string is stretched, every note will rise in pitch. Therefore, all fretted tones would sound sharp. However, with the right position of the saddle and precise placements of the frets, all fretted notes will sound sharp by the same amount. With the right nut compensation, the pitch of the unfretted (i.e., open) strings will rise the same amount that the fretted notes do (because of the proper saddle position). Thus, these adjustments combined with lowering the tension of the string from that required by an unfretted instrument will allow all tones to be exact.

• Konrad Schwingenstein: Intonation of stringed instruments with straight frets , http://www.pepithesecond.com

• Musical tuning