Reverberation (also known as reverb), in acoustics, is a persistence of sound after it is produced. Reverberation is created when a sound or signal is reflected. This causes numerous reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space – which could include furniture, people, and air. This is most noticeable when the sound source stops but the reflections continue, their amplitude decreasing, until zero is reached.

Reverberation is frequency dependent: the length of the decay, or reverberation time, receives special consideration in the architectural design of spaces which need to have specific reverberation times to achieve optimum performance for their intended activity. In comparison to a distinct echo, that is detectable at a minimum of 50 to 100 ms after the previous sound, reverberation is the occurrence of reflections that arrive in a sequence of less than approximately 50 ms. As time passes, the amplitude of the reflections gradually reduces to non-noticeable levels. Reverberation is not limited to indoor spaces as it exists in forests and other outdoor environments where reflection exists.

Reverberation occurs naturally when a person sings, talks, or plays an instrument acoustically in a hall or performance space with sound-reflective surfaces. Reverberation is applied artificially by using reverb effects, which simulate reverb through means including echo chambers, vibrations sent through metal, and digital processing.

Although reverberation can add naturalness to recorded sound by adding a sense of space, it can also reduce speech intelligibility, especially when noise is also present. People with hearing loss, including users of hearing aids, frequently report difficulty in understanding speech in reverberant, noisy situations. Reverberation is also a significant source of mistakes in automatic speech recognition.

Dereverberation is the process of reducing the level of reverberation in a sound or signal.