長阿含經 4.p36

4.p36

“‘After he spoke this verse, Brahmā Kumāra addressed the Trāyastriṃśa gods, “When someone’s voice is pure in five ways, it comes to be called Brahmā’s voice. What are the five? 1. Their voice is genuine, 2. their voice is gentle, 3. their voice is clear, 4. their voice is sonorous, and 5. it’s heard all around and far away. A voice that has these five qualities is called Brahmā’s voice.