Rosen is a lightweight mod that aims to expand on the noteblock system by adding more instruments, while trying to keep the sound design on the same level as the vanilla Minecraft.

Currently Rosen adds 18 new carefully crafted instruments such as Saxophone, Organ, Sitar, Music Box, Timpani and more! Rosen also features a Quality of Life addition that allows to play already existing instruments with the other blocks of a similar type.

№	Instrument	Blocks
1	Accordion	Honey Block, Honeycomb, Bee Nest
2	Beach	All full coral blocks (including dead)
3	Carillon	All copper blocks
4	Choir	Sculk, Sculk Catalyst
5	Dholak	All terracotta blocks (including glazed), Decorated Pot
6	Kick	End Stone, End Stone Bricks
7	Log Drum	Bamboo Block, Stripped Bamboo Block, Bamboo Planks, Bamboo Mosaic
8	Music Box	Lapis Block
9	Organ	Netherrack, all Nether bricks
10	Piano	All full quartz blocks
11	Power Guitar	Coal Block
12	Saxophone	Melon
13	Sitar	Dried Kelp Block
14	Synth	Purpur Block, Purpur Pillar
15	Synth Bass	Shroomlight, all mushroom blocks, all wart blocks
16	Timpani	Mud, Muddy Mangrove Roots, Packed Mud, Mud Bricks
17	Vibraphone	All prismarine blocks, Sea Lantern
18	Violin	Snow Block, Powder Snow

How to add custom instruments (1.21.1+ only):

In your datapack, add a new json file named after your instrument to data/rosen/noteblock_instrument/ that follows this format:

{
 "name": "<instrument_name>",
 "sound_event": "<sound>"
}

Next, add a new file data/<namespace>/tags/block/<instrument_name>_noteblocks.json for the respective block tag that defines blocks to be used for your instrument that follows regular tag format:

{
  "values": [
    "<block>",
    "<other_block>",
    "<another_block>",
    ...
  ]
}

Voilà!