From soothing drones and chimes to the sound of rain gently tapping on the roof - ambient music is transforming the way people sleep, focus and relax. Once an esoteric 1970s genre, mood music playlists have become a daily habit for millions. An official playlist on Spotify called Deep Focus has 4.8 million likes and another called Ambient Relaxation has 1.2 million. Similar lists attract millions of listeners on Apple Music and YouTube. The BBC has also embraced the trend for musical sleep and