Reverb is reflected sound that creates the impression of space. With reverb, many reflections with different durations are generated, which are heard at irregular intervals together with the original signal.
Reverb is used synonymously with reverberation and is crucial for the sound of a room. Only through reverberation can individual sound sources be positioned and better perceived. An orchestra only experiences the spatial positioning, the necessary separation and depth of the instruments through reverberation. The nature of the reflecting walls is decisive for the sound image. While smooth and hard surfaces reflect sound more or less completely, structured surfaces and soft materials such as fabrics or carpets absorb higher frequencies disproportionately. Medium and low frequencies are hardly absorbed, so the sound image is shifted towards lower frequencies.
Like sound, reverberation decreases proportionally with distance. The sound that is reflected first is called initial reflection. This in turn is reflected in more diffuse reflections on walls and floors, thus conveying the impression of space, hence the term diffuse reverb.
In the early days of audio technology, reverberation was technically generated with reverb springs or steel plates, or in echo chambers. In the case of the reverb spring, the delay of a mechanical spring with variable spring lengths was used to simulate the running times. The principle of the steel plates was based on the fact that one set a steel plate with electromechanical transducers into audio oscillations, which were reflected at the edges of the steel plate and taken up by several shifted microphones. The time of flight in the steel plate and the offset microphones allowed reverberation signals to be mixed from the various signals. With digital technology, reverb can be realized electronically. With this technique, certain reflection points are simulated.
In addition to the aforementioned reverb techniques, there is also the technique of impulse convolution. In this computationally intensive technique, the intersections of the frequency spectra of two signals are combined.