Here is the full list of all 76 String Theory achievements.
Read the book.
Complete levels 3 & 4 with the String Theory BGM. Unlocks the Harp instrument.
Complete levels 1 & 2 with the Piano Rock BGM. Unlocks the Piano instrument.
Complete the tutorial.
Complete levels 5 & 6 with the Bassic BGM. Unlocks the Electric Guitar instrument.
Complete levels 7 & 8 with the Groove McSmooth BGM. Unlocks the Drawbar Organ instrument.
Complete levels 9 & 10 with the Got Da Blues BGM. Unlocks the Saxophone instrument.
Complete levels 11 & 12 with the Hardlectro Swing BGM. Unlocks the Detroit Talker instrument.
Complete levels 13 & 14 with the Root Toot BGM. Unlocks the Trumpet instrument.
Complete levels 15 & 16 with the Me Time BGM. Unlocks the Dudes instrument.
Complete levels 17 & 18 with the Bario Paint BGM. Unlocks the Doge instrument.
Complete levels 19 & 20 with the Bro, U Lift? BGM. Unlocks the Rave Baby instrument.
Complete levels 21 & 22 with the I Wub You BGM. Unlocks the The Robot Speaks instrument.
Complete levels 23 & 24 with the Little Gray Box BGM. Unlocks the 2A03 Chip instrument.
Complete Levels 25 & 26 with the Ponsive BGM. Unlocks the Celestial Bells instrument.
Complete levels 27 & 28 with the Prom from the Past BGM. Unlocks the Clarinet Instrument.
Complete levels 29 & 30 with the Ruthless Aggression BGM. Unlocks the Hoover instrument.
Complete levels 31 & 32 with the Sassy Pants BGM. Unlocks the Hornet Sting instrument.
Complete levels 33 & 34 with the That’s Dirty BGM. Unlocks the Bass Section instrument.
Complete levels 35 & 36 with the See Sixty For BGM. Unlocks the C64 Sid Chip instrument.
Complete levels 37 & 38 with the Rock it Man BGM. Unlocks the Mechanical Cat instrument.
Complete levels 39 & 40 with the Saturn BGM. Unlocks the Crybaby Keys instrument.
Complete all the BGM challenges.
Complete level 10 without using a power-up.
Complete level 20 without using a power-up.
Complete level 30 without using a power-up.
Complete level 40 without using a power-up.
Complete all the ear-training challenges.
Complete levels 1 through 5 in Time-Attack mode.
Complete levels 6 through 10 in Time-Attack mode.
Complete Level 15 in Time-Attack mode.
Complete Level 20 in Time-Attack mode.
Complete Level 25 in Time-Attack mode.
Complete Level 30 in Time-Attack mode.
Complete Level 35 in Time-Attack mode.
Complete Level 40 in Time-Attack mode.
Complete all Time-Attack challenges.
Complete 10 level-5 puzzles in Endless mode.
Complete levels 10 level-10 puzzles in Endless mode.
Complete 10 level-15 puzzles in Endless mode.
Complete 10 level-20 puzzles in Endless mode.
Complete 10 level-25 puzzles in Endless mode.
Complete 10 level-30 puzzles in Endless mode.
Complete 10 level-35 puzzles in Endless mode.
Complete 10 level-40 puzzles in Endless mode.
Complete all Endless challenges.
Complete the Audio Stream, Beats Per Minute, and Musicologist achievements.
complete Level 5 in Chaos mode.
Complete Level 10 in Chaos mode.
Complete Level 15 in Chaos mode.
Complete Level 20 in Chaos mode.
Complete Level 25 in Chaos mode.
Complete Level 30 in Chaos mode.
Complete Level 35 in Chaos mode.
Complete Level 40 in Chaos mode.
Complete Level 1 in Chaos mode.
Complete levels 1 through 5 in Time-Attack Chaos mode.
Complete levels 6 through 10 in Time-Attack Chaos mode.
Complete levels 11 through 15 in Time-Attack Chaos mode.
Complete levels 16 through 20 in Time-Attack Chaos mode.
Complete levels 21 through 25 in Time-Attack Chaos mode.
Complete levels 26 through 30 in Time-Attack Chaos mode.
Complete levels 31 through 35 in Time-Attack Chaos mode.
Complete levels 36 through 40 in Time-Attack Chaos mode.
Complete all Time-Attack Chaos challenges. Unlocks the Zither instrument.
Complete 10 level-5 puzzles in Endless Chaos mode.
Complete levels 10 level-10 puzzles in Endless Chaos mode.
Complete 10 level-15 puzzles in Endless Chaos mode.
Complete 10 level-20 puzzles in Endless Chaos mode.
Tonal Toughness 10 level-25 puzzles in Endless Chaos mode.
Complete 10 level-30 puzzles in Endless Chaos mode.
Complete 10 level-35 puzzles in Endless Chaos mode.
Complete 10 level-40 puzzles in Endless Chaos mode.
Complete all Endless Chaos challenges.
Complete the Tuned In, Composer, and It’s a Latter achievements.
Complete all the achievements.