Reverberation
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When sound is produced in a space, multiple reflections may build up and blend together, creating reverberation, or reverb. This is most noticeable when the sound stops but the reflections continue, decreasing in amplitude, until they can no longer be heard. The time it takes for the sound pressure level of the reverberation to decay 60 decibels is known as the reverberation time, or RT(60).
Reverberation is the persistence of sound in a particular space. Large chambers, especially such as cathedrals, gymnasiums, indoor swimming pools, large caves, etc. are examples of spaces where the reverberation can clearly be heard. Reverberation can make it difficult to hear speech. If the reverberation from one syllable overlaps the next syllable it may make it impossible to hear. For instance, "cat", "cab", and "cap", may all sound the same. This loss of information makes reverb a useful tool in studios for "smoothing" sounds; a common application is on vocals to help generate the illusion of consistent pitch. Traditionally, this was achieved by recording sounds in reverberant chambers, but modern recording technology allows for analogue and digital processors which can simulate a wide range of spaces.
Different types of music tend to sound best with different reverberation times; during a live performance, classical music and choral music tend to require longer reverberation times than modern rock and popular music, for example. Pauline Oliveros, Stuart Dempster, and especially their group the Deep Listening Band have performed in very reverberant spaces, such as the Fort Warden Cistern, which has a reverberation time of 45 seconds (this must be 4.5 seconds or 4 to 5 seconds, as 45 seconds cannot be obtained in even the most expensively designed reverberation chambers which have reverberation times of about 10 seconds at best).
Reverberation times can differ depending on a frequency band, which is defined by the acoustic properties of the space.
- [Short sample of reverberation effect] ([file info])
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- * Problems listening to the file? See [Media helpmedia help].
The sound decay rate
In small rooms like damped living rooms you cannot speak of hearing the reverberation time. Therefore we use often the sound decay rate.
The sound decay rate is the time rate at which sound pressure level decreases in a room at a stated frequency. The unit is decibel per second (dB/s). The decay rate DR in a reverberant room is related to reverberation time by RT60 = 60 dB / DR.
Often the reverb time is called sound decay rate, which is wrong. Reverb time in seconds and sound decay in decibel per second cannot be identical.
External links
- [Articles on Reverb and all other Sound Definitions]
- [How reverb has shaped modern music] at [Sweetwater.com]
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