It's easy to hear why the sweet, emotionally vibrant and irresistible pop sound of producer Irwan "Opung" Simanjuntak is the soundtrack to romances in Indonesia and beyond. His growing list of collaborations—including with the likes of Glenn Fredly and Afghan—show a deft touch, using silky R&B, acoustic piano and gentle guitar to underscore exquisite melodies, allowing gifted singers to shine.