A unison is the relationship of the two or three strings that together make up a note for most of the piano. If the strings of a given note aren’t tuned exactly the same, the slightly different pitches produce an ‘out of phase’, or ‘wow-wow-wow’ sound, a regularly repeating beat rate. This unison beating gets slower as the two somewhat different pitches get closer to being the same, then disappears altogether when the two pitches are exactly the same.
When I started in the tuning program at NEC, we learned how to hear and tune unisons by lowering the pitch for one of two strings, then bringing the pitch back up until it matched exactly the other string. We spent a lot of time raising the string too far, then lowering it too much, back and forth. It can be hard to get it perfect right away. This is a good way to get started with practicing tuning.
Interval relationships are how any two notes of an interval interact. In piano tuning, each note is tuned by comparing it to another reference note, using intervals. This is the edge of the cliff right here – if you don’t want to permanently change the way you hear music, STOP READING. Once shown the relationships of intervals from a tuning perspective, it is impossible to un-learn.
Here are some common intervals used in tuning and their relationships:
Thirds – In the temperament section of the piano, thirds have a “beat rate” that gets progressively faster until it gets so rapid that it’s hard to hear. Take the F3A3 third, for example. These two notes together should have a beat rate of seven beats per second. This rate gets progressively slower when moving down the keyboard, faster when moving up.
Fourths – Fourths are almost pure intervals, meaning that both notes interact in a way that produces almost no beat rate. A fourth is a slightly expanded interval, which makes it wider than a pure beatless fourth. Unlike the thirds, fourths remain slightly expanded throughout the entire keyboard.
Fifths – Fifths are almost pure intervals, much like the fourths, except they are slightly contracted. This makes it narrower than a pure (beatless) fifth. Also like the fourths, the fifths remain slightly contracted throughout the keyboard.
Sixths – Sixths have beat rates much like thirds. For example, the A3-C#4 third vs. the A3-F#4 sixth: the sixth will have a beat rate of roughly double that of the third. In the middle section of the piano, where the beat rates are slow enough to be able to hear, thirds and sixths with the same base note will have this same relationship. Like thirds, the beat rate gets progressively slower when moving down the keyboard, faster when moving up.
Octaves – Stretching an octave to address inharmonicity (see stretching the tuning) means making the octave slightly wider than a pure octave. As covered later, just how wide to stretch an octave is really a matter of personal preference and what sounds best to the tuner.
If you are confused about all this talk of interval relationships and beat rates – just relax. This is where one of the major benefits of this website really comes through – not only do I describe what to listen for, you get to hear it for yourself. Knowing how each interval should sound and how they all interact together comes with time and patience, so don’t get too frustrated if it doesn’t come right away.