The reflection of sound is the basis of reverb, and it is similar to an echo. Except, unlike an echo, which is the single reflection of a sound wave, reverb is the sum of multiple reflections. This causes a stereo effect in the reverberation. In an example, a source produces a single sound; this sound reaches the listener's ears first, but solid surfaces also reflect the sound. These reflected sounds reach the listener later then the initial sound and, depending on the amount of reflection, at lower decibels, causing multiple distant echo-like effects.
Stereo reverberation has been in use for thousands of years, although the first users did not realize it. Musicians who played in concert halls, churches and other wide-open structures, achieved the first reverb. These made for better sounding performances as opposed to parlors or small buildings. In 1895, a physicist named Wallace Sabine discovered the first formula for predicting a room's reverb, thus starting the science of room acoustics. Through his works the basis for concert hall building, based on reverb, was developed.
Since reverb was usually only achievable during live performances, and based on the performance's venue, to transmute reverb onto recordings an artificial reverb method was developed. The initial sound was transferred to another room via speaker, rerecorded by a microphone in the room and then sent back to the mixer for mixing with the initial sound. As technology advanced, so did the method of creating reverb, but all methods were based on this first method. The first methods, however, most commonly produced a mono reverberation. It was not until the usage of stereo speakers that these methods were starting to produce stereo reverberation.
With the use of an analog delay and low frequency oscillator, reverb was brought into the digital age in the 1970s. The original signal was passed through the analog delay, causing multiple signals to be produced. These extra signals were then pushed through the LFO causing them to change velocity and time. When all of these signals were played back at once, it produced the same effect as a traditional stereo reverberation. This method not only reduced space requirements, but also made reverb a more user-friendly effect.
Since a recorded track does not produce the same reverb as a concert hall, a new process was developed to try to recreate the stereo reverberation of a concert hall. By playing a single track from various speakers, and applying a lag to certain speakers, it became possible to simulate the reverberation that a concert hall produces. This simulated reverb became the basis for the surround sound systems that have become popular in home theater setups.