The Sound Mode (also known as Sound Test or Sound Select, among other names) is an option that appears in certain Castlevania games. It allows the player to listen to the music of the game, as well as some sound effects.
Game specific information
Obtain the "Good Ending" of the game (find all relics, wear both JB's and MK's Bracelets when defeating Maxim, and defeat Dracula Wraith's second form). The Sound Mode option will then become available on the title screen menu.