TuneHaven

What cents mean, and when "in tune" is in tune

A cent is a hundredth of a semitone. Here is how many of them you can actually hear, why ±5 is the usual target, and why a tuner that flashes green instantly is lying to you.

The number next to the note on your tuner is cents. A cent is one hundredth of a semitone, so there are 1200 of them in an octave.

Cents exist because pitch is logarithmic. The gap between two adjacent notes is much wider in hertz at the top of an instrument than at the bottom: an A4 to A#4 step is about 26 Hz, while E1 to F1 is about 2.5 Hz. Measuring error in hertz would mean “5 Hz sharp” was trivial in one place and enormous in another. Cents make the number mean the same thing everywhere.

How much can you hear

Roughly:

  • Under 3 cents is inaudible to almost everyone on a single sustained note
  • 5 cents is where a good ear starts to notice on a held note, especially against another instrument
  • 10 cents is clearly audible to most players when two notes sound together
  • 20 cents and up sounds plainly out of tune to anyone in the room

Two notes played together are far more revealing than one note alone, because you hear the beating between them rather than having to judge pitch from memory. This is why a chord exposes tuning problems that individual strings did not.

Why ±5 cents is the usual target

It is close enough that the error is inaudible in practice, and loose enough to actually reach on a real instrument in a real room.

Chasing zero is not worth it, for a reason that has nothing to do with your patience: the instrument will not hold it. Fretting a note pulls it sharp. Temperature shifts everything. A string’s pitch changes over the first seconds after you pluck it. Landing inside ±5 and moving on is the correct engineering answer.

Why an instant green light is a lie

A plucked string is not one stable pitch. In the first fraction of a second the attack is chaotic and the reading swings around. Then the pitch settles, and as the note decays, tension effects pull it slightly again.

A tuner that turns green the moment the reading first touches the target is reporting a transient, not a state. It will happily flash green on a string that is passing through the right pitch on its way somewhere else. This is the behaviour that leaves people confident their guitar is fine right up until the first chord.

TuneHaven requires the pitch to hold inside the tolerance briefly before it commits to saying “in tune”. That is the difference between “this was momentarily correct” and “this is correct”. The meter itself keeps moving continuously the whole time, so you can always see what the string is doing rather than watching a frozen display.

The same principle explains why it will not freeze the needle on the last good reading when the sound fades. A stationary needle that reflects a note which stopped two seconds ago looks like information and is not.

Sharp and flat

Sharp means too high, and the tuner shows a positive number. Loosen the string.

Flat means too low, and the number is negative. Tighten it.

Wherever possible, arrive at the target from below. Coming down onto a note leaves tension unevenly distributed through the nut and the tuning post, and it releases as you play, dropping the string flat again within a minute.