Good intonation on the guitar means that from fret to fret all the way up the scale, the ratios of the notes are in proper relationship to one another. (Recall the ‘Word For The Day’ on Just and Equal Temperament.) Put simply, when you play the note E on the first string 12th fret, and then play F (or any other note above it) the F does not sound sharp or flat in relation to E. Intonation on a guitar is adjusted at the bridge using a chromatic tuner. Random movement of the bridge will not solve the problem. If you don’t know how to make this adjustment, take the guitar to a qualified technician. A warped neck can also cause intonation problems, which again, is a job for Super Guitarman (Don’t worry about how to find him, every town’s got one).
So what happens if a guitarist shows up to a session, you notice some intonation or pitch problems, and since the clock is ticking, you can’t send him off to a luthier? Plug-ins like the Antares Auto Pitch Correct, have become an essential tool for correcting intonation or pitch problems (particularly vocals) and can create performances that are perfectly in tune without significant change in sound quality. Of course, this can only work monophonically, that is, on solo or single string playing, which makes them quite handy for bass guitar as well. Chords cannot be put in tune by pitch correction devices. Sometimes adding a chorus effect may help out-of-tune chords (usually it makes things worse) by shifting pitch to make the pitch center a bit ambiguous. By shifting pitch up and down, our ear picks out an average center pitch, creating the illusion of proper pitch. In essence, it’s what a vibrato on a fretless instrument does. As we move our finger back and forth on a violin, for example, we are shifting pitch up and down, and interestingly enough, our ear finds this pleasing. Chorus can also make an out of tune synth string part sound better for the same reason. In the absence of a pitch-correcting device, there is a little trick that can help if the guitar’s intonation is bad or the strings are old. Old strings tend to go flat above the 12th fret. You can prove this by playing the harmonic of each string at the 12th fret, and then playing the note normally. The note will sound flat in relation to the harmonic. Either make the guitarist get new strings, or use a tuner to tune the guitar so that the notes at the 12th fret are in tune. This will make the strings a little sharp. Record the solo with the strings tuned normally on one track, and then record the solo with them retuned on another track. Comp the tracks using the sharp tuning for notes that sound flat. It’s extra work, but sometimes in recording, we need to make do at the moment.