The traditional 樂 pictured a wooden frame strung with silk and drums — a complete orchestra in one glyph. Music and joy shared the character from the beginning: the ancients saw no difference worth writing down.
One character, two readings, one philosophy: yuè is music (音乐), lè is joy (快乐 happy, 可乐 cola — 'drinkable joy'). Confucius made the pun canonical: asked about music (乐), scholars note the same character answers as happiness. 乐观 is optimism; 助人为乐 — helping others as one's joy. Birthday wishes (生日快乐), New Year wishes (新年快乐): Chinese celebration is powered by 乐.
Strings and drums on a stand — MUSIC (yuè), which is JOY (lè).
音乐 (music) and 快乐 (happy) share 乐 — in Chinese, the art and the emotion were never separated.