Perceiving Soun — Kwan Um School of Zen

Perceiving sound means everything is universal sound: birds singing, thunder, dogs barking—all this is universal sound. If you have no mind, everything will be perceived just as it is. Therefore, when you are chanting with no mind it is also universal sound. If you have “I” then it is “my” sound. But with a mind clear like space, sometimes even the sound of a dog barking or a car horn honking will bring enlightenment because at that moment you and the sound become one. When you and the sound become one, you don't hear the sound, you are the sound.

Foreword from the KUSZ Chanting Book
By Zen Master Seung Sahn

Check out a clip from the Kwan Um Zen Online Study Group, Insight into Non-Self.