An echo is a reflection of sound waves off a surface, resulting in a delayed repetition of the original sound. The time difference between the original sound and the echo is determined by the distance between the source of the sound and the reflecting surface.
When sound waves propagate through the air and encounter a reflective surface, such as a wall or a canyon wall, a portion of the sound energy is reflected back towards the source. This reflection occurs due to the difference in the acoustic impedance (the resistance to sound propagation) between the air and the reflective surface.
The time delay of the echo is determined by the round-trip distance traveled by the sound waves, which includes the distance from the sound source to the reflective surface and back to the listener or recording device. The speed of sound in air is approximately 343 meters per second (depending on factors such as temperature and humidity), so the time delay can be calculated by dividing the round-trip distance by the speed of sound.
For example, if the reflective surface is located 10 meters away from the sound source, the sound waves would take approximately 29 milliseconds (0.01 seconds) to travel to the surface and back.
It's worth noting that the properties of the reflective surface can also affect the characteristics of the echo. Different surfaces have different acoustic properties, such as absorption and reflection coefficients, which can influence the intensity and quality of the reflected sound. So, the nature of the reflective surface can impact not only the timing but also the overall characteristics of the recorded echo.