Music timbre information (e.g. duty cycle) for tracks in Metroid is hard-coded in an extremely limiting and romhacker-hostile manner that makes it difficult to configure the timbre as desired when modifying the game’s music. This small patch replaces the original system for specifying timbre with a simple table of values that can be easily modified in new hacks.

This hack is for romhackers who are developing their own Metroid hacks only. It does nothing visible to players.

This hack is based on the following USA version of Metroid, though other versions that contain the same data at the same locations may work as well:
File SHA-1: ECF39EC5A33E6A6F832F03E8FFC61C5D53F4F90B
File CRC32: A2C89CB9
ROM SHA-1: FDBFC7871962F72A1EF57E5A7E456164FB93430B
ROM CRC32: 70080810