Sound test
A sound test is a function built into the options screen of many video games. This function was originally meant to test whether the game's music and sounds would function correctly, as well as giving the player the ability to compare samples played in Monaural, Stereophonic and later Surround sound.
In modern times, most sound tests function mostly as a jukebox to listen to the game's music, sound effects, and voice tracks for enjoyment. They are also sometimes used as a place to enter cheat codes.
Sound test and cheat codes
Some games feature cheat codes related to the sound test. Usually, songs need to be played in a particular order. For instance, in Sonic the Hedgehog 2, it is possible to select levels in this manner.
In some games, a cheat code might be necessary to reach the sound test screen (such as in Sonic the Hedgehog 3), or some other specific method is needed to unlock it, such as "buying" it with earned credit for achievements in-game.
In other games, the sound test is unrelated to cheat codes and is often among the last items to be unlocked. Alternatively, in some games the sound test is available from the beginning, and expands as the player encounters new sounds or music during normal gameplay.