Custom Instrument Tracks

First, prepare a sound file in the Sound/Instrument folder, with filename using one of the following Sound ID:

In Game Instruments Sound ID

Instrument ID	Sound ID	CN	EN	JP
trumpet	trumpet_practice	喇叭	trumpet	トランペット
piano	piano_kanon	三角钢琴	grand piano	グランドピアノ
piano2	piano_neko	钢琴	piano	ピアノ
piano_killkill	piano_neko	杀杀钢琴	kill kill piano	キルキルピアノ
piano_gould	piano_gould	古尔德钢琴	Gould's piano	グールドのピアノノ
harpsichord	harpsichord_goldberg	大键琴	harpsichord	チェンバロ
guitar_ash	guitar_caccini	阿什的吉他	Ash's guitar	アッシュのギター
guitar_efrond	guitar_dusk	埃夫隆德的吉他	Efrond's guitar	エフロンドのギター
guitar	guitar_air	吉他	guitar	ギター
harp	harp_komori	竖琴	harp	ハープ
panty	violin_chaconne	内裤	panty	パンティー
lute	guitar_sad	鲁特琴	lute	リュート
shield_lute	guitar_sad	乌德琴	Al'ud	アル・ウード
recorder	recorder	竖笛	recorder	リコーダー
flute	flute	长笛	flute	フルート
taiko	taiko	太鼓	taiko	太鼓
drum	drum	鼓	drum	鼓
mokugyo	mokugyo	木鱼	wooden gong	木魚
tambourine	tambourine	铃鼓	tambourine	タンバリン
mic	mic_rachmaninoff	麦克风	mic	マイク
cello	cello_prelude	大提琴	cello	チェロ
instrument_violin	violin_chaconne	小提琴	violin	ヴァイオリン
panty	violin_chaconne	小提琴	panty	パンティー
stradivarius	violin_furusato	斯特拉迪瓦里	stradivarius	ストラディバリウス
koto	koto	古筝	koto	琴
sax	trumpet_practice	萨克斯	sax	サックス

If you are making a new instrument, use instrument's ID (Thing ID) as Sound ID.

Launch the game once to generate a metadata json file for the newly added sound, exit game, edit the metadata json to use "type": BGM, and add some parts for the instrument play:

cello_prelude.json

{
    "type": "BGM",
    "id": -1,
    "loop": 0,
    "minInterval": 0.0,
    "chance": 1.0,
    "delay": 0.0,
    "startAt": 0.0,
    "fadeAtStart": false,
    "fadeLength": 0.0,
    "volume": 0.5,
    "volumeAsMtp": false,
    "allowMultiple": true,
    "skipIfPlaying": false,
    "important": false,
    "alwaysPlay": false,
    "noSameSound": false,
    "pitch": 1.0,
    "randomPitch": 0.0,
    "reverbMix": 1.0,
    "spatial": 0.0,
    "bgmDataOptional": {
        "day": false,
        "night": false,
        "fadeIn": 0.1,
        "fadeOut": 0.5,
        "failDuration": 0.7,
        "failPitch": 0.12,
        "pitchDuration": 0.01,
        "parts": [
            {
                "start": 0.0,
                "duration": 4.0
            },
            {
                "start": 4.0,
                "duration": 4.0
            },
            {
                "start": 8.0,
                "duration": 4.0
            },
            {
                "start": 12.0,
                "duration": 4.0
            },
            {
                "start": 16.0,
                "duration": 4.0
            }
        ]
    }
}

Each part has a start timestamp and a duration in seconds. Parts will be randomly selected during instrument play.