See also: Adding custom hitsounds
Hitsounds are the sounds that osu! plays in response to user input when interacting with hit objects. Hitsounds are typically used to give auditory feedback to the player to help them judge their accuracy in relation to the song.
Hitsound feedback consists of a default sample called a "hit normal", and any combination of whistle, finish, or clap sample additions. Each sample has one of three "sample sets" that change its style:
Beatmappers can replace any default sound samples with custom samples using a beatmapset's folder. A player's skin can also replace default hitsounds on all beatmaps. Details on hitsound samples can be found in the hitsound skinning article.
An active hitsound correlates to a player's clicking by reaching its peak impact immediately when played. Drum sound samples are the most frequently used active hitsounds because they provide clear and immediate feedback.
A passive hitsound does not correlate to a player's clicking. These are usually sound effects that accompany active hitsounds.
Hitsounds can be added through storyboarding, but because they don't correlate to a user's clicking, they are also classified as passive.
A keysound is a hitsound sample that is extremely similar to, or directly taken from, the song and is used to replicate the pitch of the song's notes. This method of hitsounding usually provides low feedback to the player, but can make playing certain beatmaps more interesting and make sections of a map stand out when applied well.
Unlike the other game modes, osu!taiko hitsounds directly affect the gameplay of their maps. Kats are distinguished from Dons using whistles and claps, and large notes are distinguished from normal ones using finishers.
osu!taiko's default samples are unique to the mode, and mappers typically do not override them.