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Information about Reverberation

This article is about audio effect. For other uses, see Reverb (disambiguation).


Reverberation is the persistence of sound in a particular space after the original sound is removed. When sound is produced in a space, a large number of echoes build up and then slowly decay as the sound is absorbed by the walls and air, creating reverberation, or reverb. This is most noticeable when the sound source stops but the reflections continue, decreasing in amplitude, until they can no longer be heard. Large chambers, especially such as cathedrals, gymnasiums, indoor swimming pools, large caves, etc., are examples of spaces where the reverberation time is long and can clearly be heard. Different types of music tend to sound best with reverberation times appropriate to their characteristics.

(Compare with echo: "If so many reflections arrive at a listener that he is unable to distinguish between them, the proper term is reverberation.")

Clean signal, followed by different versions of reverberation (with longer and longer decay times).
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Reverberation Time

RT60 is the time required for reflections of a direct sound to decay by 60 dB below the level of the direct sound. Reverberation time is defined for wide band signals. When talking about the decay of an individual frequency, the term decay time is used.

In the late 19th century, Wallace Clement Sabine started experiments at Harvard University to investigate the impact of absorption on the reverberation time. Using a portable wind chest and organ pipes as a sound source, a stopwatch and a clean pair of ears he measured the time from interruption of the source to inaudibility (roughly 60dB). This time varies directly with the dimensions of room but inversely as the absorption present.

The best reverberation time for a space in which music is played depends on the size of the room and the type of music. Rooms for speech require a shorter reverberation time than for music. A longer reverberation time can make it difficult to understand speech. If the reverberation time from one syllable over laps the next syllable, it may make it difficult to identify the word [1]. "Cat", "Cab", and "Cap" may all sound very similar. If on the other hand the reverberation time is too short, tonal balance and loudness may suffer. Reverberation effects are often used in studios to "smooth" sounds; the effect is commonly used on vocals to help remove inconsistencies in pitch.

Basic factors that affect a room's reverberation time include the size and shape of the enclosure as well as the materials used in the construction of the room. Every object placed within the enclosure can also affect this reverberation time, including people and their belongings.

The Sabine Equation

Sabine's reverberation equation was developed in the late 1890s in an empirical fashion. He established a relationship between the RT60 of a room, its volume, and its total adsorption (in sabins). This is given by the equation:

.


where is a mathematical constant measuring 0.161, is the volume of the room in m³, total surface area of room in m², is the average adsorption coefficient of room surfaces, and is the total adsorption in sabins.

It is worth noting that the total absorption in sabins (and hence reverberation time) generally changes depending on frequency (dependent on the which is defined by the acoustic properties of the space), and that the equation does not take into account room shape or dimensions, nor losses from the sound travelling through the air (important in larger spaces). In general most rooms adsorb less in the lower frequencies, causing a longer decay time.

The reverberation time RT60 and the volume V of the room have great influence on the critical distance dc (conditional equation):



where critical distance is measured in metres, volume is measured in m³, and reverberation time is measured in seconds.

Absorption

The absorption coefficient of a material is a number between 0 and 1 which indicates the proportion of sound which is absorbed by the surface compared to the proportion which is reflected back into the room. A large, fully open window would offer no reflection as any sound reaching it would pass straight out and no sound would be reflected. This would have an absorption coefficient of 1. Conversely, a thick, smooth painted concrete ceiling would be the acoustic equivalent of a mirror, and would have an absorption coefficient very close to 0.

Measurement of Reverberation Time

Historically reverberation time could only be measured using a level recorder (a plotting device which graphs the noise level against time on a ribbon of moving paper). A loud noise is produced, and as the sound dies away the trace on the level recorder will show a distinct slope. Analysis of this slope reveals the measured reverberation time. Modern digital sound level meters carry out this analysis automatically, on digital data.

Two basic methods exist for creating a sufficiently loud noise (which must have a defined cut off point). Impulsive noise sources such as a blank pistol shot, or balloon burst may be used to measure the impulse response of a room. Alternatively, a random noise signal such as pink noise or white noise may be generated through a loudspeaker, and then turned off. This is known as the interrupted method, and the measured result is known as the interrupted response.

Reverberation time is often given as a measurement of decay time. Decay time is the time it takes the signal to diminish 60 dB below the original sound.

Creating Reverberation Effects

It is often desirable to create a reverberation effect for recorded or live music. A number of systems have been developed to facilitate or simulate reverberation.

Chamber reverberators

The first reverb effects created for recordings used a real physical space as a natural echo chamber. A loudspeaker would play the sound, and then a microphone would pick it up again, including the effects of reverb. Whilst this is still a common technique, it requires a dedicated soundproofed room, and varying the reverb time is difficult.

Plate reverberators

A plate reverb system uses an electromechanical transducer, similar to the driver in a loudspeaker, to create vibration in a large plate of sheet metal. A pickup captures the vibrations as they bounce across the plate, and the result is output as an audio signal.

Spring reverberators

“Spring reverb” redirects here. For the album Spring Reverb, see Spring Reverb (album).


A spring reverb system uses a transducer at one end of a spring and a pickup at the other, similar to those used in plate reverbs, to create and capture vibrations within a metal spring. Guitar amplifiers frequently incorporate spring reverbs due to their compact construction and low cost. Spring reverberators were once widely used in semi-professional recording due to their modest cost and small size. Due to quality problems and improved digital reverb units, spring reverberators are declining rapidly in use.

Many musicians have made use of spring reverb units by rocking them back and forth, creating a thundering, crashing sound caused by the springs colliding with each other.

Digital reverberators

Digital reverberators use various signal processing algorithms in order to create the reverb effect. Since reverberation is essentially caused by a very large number of echoes, simple DSPs use multiple feedback delay circuits to create a large, decaying series of echoes that die out over time. More advanced digital reverb generators can simulate the time and frequency domain responses of real rooms (based upon room dimensions, absorption and other properties). In real music halls, the direct sound always arrives at the listeners ear first because it follows the shortest path. Shortly after the direct sound, the reverberant sound arrives. The time between the two is called the 'arrival time gap'. This gap is important in recorded music because it is the cue that gives the ear information on the size of the hall, better digital reverbs can incorporate this arrival time gap and hence sound more realistic. Digital reverb systems are commonly implemented as software plugins.

Convolution Reverb

Main article: Convolution reverb

External links

See also

Reverb may refer to:
  • Reverb (film), a 2007 movie
  • Reverb (night club), a Toronto night club
  • Reverb (non-profit), environmental organization that educates and engages musicians and their fans

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Sound is a disturbance of mechanical energy that propagates through matter as a wave (through fluids as a compression wave, and through solids as both compression and shear waves).
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In audio signal processing and acoustics, an echo (plural echoes) is a reflection of sound, arriving at the listener some time after the direct sound. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room.
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Reflection or reflexion may refer to:
  • Reflection (physics), a wave phenomenon commonly observed in mirrors.
  • Reflection (electrical), reflected voltage in an electrical signal due to an impedance change

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amplitude is a nonnegative scalar measure of a wave's magnitude of oscillation, that is, the magnitude of the maximum disturbance in the medium during one wave cycle.

Sometimes this distance is called the peak amplitude
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swimming pool(3,000L), swimming bath(500L), or wading pool(30 L) is an artificially enclosed body of water intended for swimming or water-based recreation. There are many standard sizes; the largest and deepest is the Olympic size.
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Reverberation is the persistence of sound in a particular space after the original sound is removed. When sound is produced in a space, a large number of echoes build up and then slowly decay as the sound is absorbed by the walls and air, creating reverberation, or reverb.
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In audio signal processing and acoustics, an echo (plural echoes) is a reflection of sound, arriving at the listener some time after the direct sound. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room.
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The decibel (dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power) relative to a specified or implied reference level.
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For the periodical, see .
The 19th Century (also written XIX century) lasted from 1801 through 1900 in the Gregorian calendar. It is often referred to as the "1800s.
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Wallace Clement Sabine (June 131868 - January 101919) was an American physicist who founded the field of architectural acoustics. He graduated from Ohio State University in 1886 at the age of 18 before joining Harvard University for graduate study and remaining as a faculty member.
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A stopwatch is a timepiece designed to measure the amount of time elapsed from a particular time when activated to when the piece is deactivated.

The stopwatch is typically designed to start at the press of the top button and stop by pressing the button a second time to
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For the computer operating system, see .
A syllable (Ancient Greek: συλλαβή) is a unit of organization for a sequence of speech sounds.
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The introduction to this article is vague. To comply with Wikipedia's guidelines, it should be improved.
Please discuss this issue on the talk page and read the to make sure the introduction summarizes the article. This article has been tagged since July 2007.
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Reverberation is the persistence of sound in a particular space after the original sound is removed. When sound is produced in a space, a large number of echoes build up and then slowly decay as the sound is absorbed by the walls and air, creating reverberation, or reverb.
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A central concept in science and the scientific method is that all evidence must be empirical, or empirically based, that is, dependent on evidence or consequences that are observable by the senses. Empirical data is data that is produced by experiment or observation.
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The Sabin is defined as a unit of sound absorption. One square meter of 100% absorbing material has a value of one metric Sabin. The unit is named in honor of Wallace Clement Sabine.
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Acoustics is the branch of physics concerned with the study of sound (mechanical waves in gases, liquids, and solids). A scientist who works in the field of acoustics is an acoustician. The application of acoustics in technology is called acoustical engineering.
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The volume of a solid object is the three-dimensional concept of how much space it occupies, often quantified numerically. One-dimensional figures (such as lines) and two-dimensional shapes (such as squares) are assigned zero volume in the three-dimensional space.
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Critical distance is, in audio physics, the distance at which the sound pressure level of the direct and the reverberant sound fields are equal when dealing with a directional source.
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1 metre =
SI units
1000 mm 0 cm
US customary / Imperial units
0 ft 0 in
The metre or meter[1](symbol: m) is the fundamental unit of length in the International System of Units (SI).
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second (SI symbol: s), sometimes abbreviated sec., is the name of a unit of time, and is the International System of Units (SI) base unit of time.

SI prefixes are frequently combined with the word second to denote subdivisions of the second, e.g.
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Sound level meters measure sound pressure level and are commonly used in noise pollution studies for the quantification of almost any noise, but especially for industrial, environmental and aircraft noise.
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When used literally, the term echo chamber refers to a hollow enclosure used to produce echoing sounds, usually for recording purposes. For example, the producers of a television or radio program might wish to produce the aural illusion that a conversation is taking place in
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microphone, sometimes referred to as a mike or mic (both IPA pronunciation: [maɪk]), is an acoustic to electric transducer or sensor that converts sound into an electrical signal.
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transducer is a device, usually electrical, electronic, electro-mechanical, electromagnetic, photonic, or photovoltaic that converts one type of energy to another for various purposes including measurement or information transfer (for example, pressure sensors).
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Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday objects are constructed of the material.
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pickup device acts as a transducer that captures mechanical vibrations (usually from suitably equipped stringed instruments such as the electric guitar, electric bass guitar or electric violin) and converts them to an electrical signal which can be amplified and recorded.
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Spring Reverb is the third studio album released by the rock and roll jam band The Big Wu. This was the last album recorded with former member Jason Fladager before he departed the band.
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