Why does my ocarina squeak on its high notes?
An ocarinas high notes can squeak for a number of reasons, here are the most common:
Blowing too hard
The high notes of any ocarina will squeak if blown too hard. If you are new to the ocarina you must learn to control your breath pressure to avoid this. Use a chromatic tuner to check the pitch of the instrument and raise or lower your pressure. Listen for the cleanest sound. Blowing the high notes too softly will result in an airy sound while blowing too hard will make them sound rough or squeak.
You may find that the ocarina plays fine flat of concert pitch but squeaks as you approach it. Please see the next point.
Playing in a cold environment
An ocarina's high notes can squeak if you attempt to play in a cold environment. The pitch of all wind instruments is affected by temperature, they play flatter when cold and sharper when hot. This can be compensated for by raising your breath but this compensation is limited. In very cold environments the high notes will squeak before they reach concert pitch. There are a number of ways of dealing with this, please see 'Playing ocarinas in tune in warm or cold environments'.
Note that 'cold' is relative: if an ocarina was tuned to play in a warm climate of 25°C, 15°C would be cold for it. In this case the high notes may be unplayable even though it does not feel cold to you.
Bad ocarina or poor tuning
If your ocarina's high notes sill squeak after checking these points there is a good chance you have a bad instrument. Unfortunately a lot of ocarinas in mainstream outlets are of very poor quality. If an ocarina is poorly tuned, its chamber volume and voicing mismatched, or a poor chamber shape used, the high notes will be prone to squeaking.
If this is the case get a better instrument. Pure Ocarinas where designed from the start as serious musical instruments.