An echo can be understood as a temporal shift in the soundwave. Our minds register the same soundwave returning to us, slightly altered by time and space. From the differences between the original and the time-shifted instances, we are able to read the material qualities of the space we are in. By listening to the echo, we gather information about the space around us and our position in it.
The fading of the echo is caused by the energy loss of sound as it spreads through space. But while the wave loses energy as it travels, it also gains new information. A sound is not just a wave but also a record of its own journey through time and space. Sounds traverse time and space, but they do not just quietly fade away. They bump into obstacles, rush through materials, losing qualities and resolution, until a filtered, broken, mangled version is left — which, as the energy fades, finally transforms from a lively wave to total stillness.
For the listener, the fading of energy and timbral changes in sounds are significant markers of their own existence. These changes on our timeline, like the tiny differences between film frames, are what animate our experience. We locate ourselves in time and space by listening to the change of the world.