Scientists use the "Haas Effect" to distinguish them. If the reflection returns in less than 50 milliseconds (ms) , the human brain merges it with the original sound (Reverb). If it returns after more than 50ms , the brain hears it as a separate event (Echo).
Occurs when a sound reflects off a distant surface (usually more than 17 meters away). Because the sound takes longer to travel, the brain perceives it as a separate event from the original sound. This typically happens with a delay of more than 50–100 milliseconds.