What is Revereberation?

Types of Reverbs - Definition and Applications of Revereberation


Reverberation

When joining an assembly inside the school hall, you must have witnessed how different the voice of the speaker appears from the original. Also, the sound created by the musical instruments in a concert in a closed hall looks very different when matched to its original sound. Ever wondered why and how? The answer to this lies in the theory of reverberation of sound.



Definition

Reverberation, in acoustics and psychoacoustics, is the persistence of a sound after the sound is made. A reverberation, or reverb, is produced when a sound or signal is reflected producing a large number of reflections to form up and then decay as the sound is absorbed by the objects in the space – which could contain people and material objects including air. This is clearly experienceable when the sound origin stops but the reflections continue, reducing the amplitude gradually to zero.

Reverberation is frequency dependent on reverberation time or the length of the decline. It is much applicable in the architectural design of spaces which require having specific reverberation times to attain optimum performance for their planned activity. In comparison to a separate echo, that is detectable at a lowest of 50 to 100 ms after the earlier sound, reverberation is the presence of reflections that arrive in a sequence of less than around 50 ms. As time goes by, the amplitude of the reflections slowly reduces to non-noticeable levels. Reverberation is not limited to indoors. It occurs in forests and other outdoor environments where reflection is present.

Reverberation happens naturally when an individual talks, sings or plays an instrument acoustically in a gallery or performance space with sound-reflective tops. The sound of reverberation is often automatically added to the vocals of singers and to musical instruments. This is done in every live sound systems and sound recordings by using effects components. Effects units that are specified in the production of the reverberation effect are usually called reverbs.

Reverberation time is calculated by the time needed for the sound to "fade away" in a surrounded area after the origin of the sound has stopped.

When it comes to precisely measuring reverberation time with a meter, the term T60 (an acronym for Reverberation Time 60dB) is used. T60 delivers a goal to reverberation time measurement. It is defined as the time it takes for the sound pressure level to decrease by 60 dB, calculated after the stimulated test signal is abruptly ended.

Reverberation time is often stated as a lone value is calculated as a wideband signal (20 Hz to 20 kHz). However, being frequency depending on, it can be more accurately defined in terms of frequency bands (one octave, 1/6 octave, 1/3 octave etc.). Being frequency dependent, the reverberation time calculated in narrow bands will vary depending on the frequency band being calculated. For exactness, it is significant to know what ranges of frequencies are being labeled by a reverberation time measurement.

Wallace Clement Sabine started experiments at Harvard University in the late 19th century, to examine the effect of absorption on the reverberation time. Using a movable wind chest and organ pipes as a sound origin, a stopwatch, and his ears, he calculated the time from interruption of the source to inaudibility (an alteration of roughly 60 dB). He establishes that the reverberation time is proportional to room sizes and inversely proportional to the amount of absorption.

The peak reverberation time for a room in which music is played depending on the kind of music that is to play in the room. Rooms used for speech naturally requires for a shorter reverberation time so that speech can be understood more clearly. If the reflected sound from one syllable is still perceived when the next syllable is articulated, it may be hard to understand what was said. "Cab", "Cap", and might all sound very alike. If on the other hand, the reverberation time is too short, tonal stability and loudness might suffer. Reverberation effects are frequently used in studios to enhance the depth of sounds. Reverberation modifies the perceived spectral structure of a sound but does not change the pitch.

Basic aspects that affect a room's reverberation time comprise the shape and size of the surrounding as well as the substance used in the building of the room. Every object located within the room can also affect this reverberation time, containing people and their belongings.

Types of Reverbs

  • 1. Chamber reverbs

  • 2. Plates reverbs

  • 3. Spring reverbs

  • 4. Digital reverbs

  • Chamber reverberators


    Chambers are the type of the opposite end of the spectrum from halls.

    Before digital reverb units, there existed a humble recording studio owner. And this studio owner desired the sound of a vast reverberant space. Unluckily, real estate being expensive, this studio owner did not have the capitals for a giant hall. So he dedicated a smaller room with highly reflective surfaces and preferably rectangle angles to the task. Because this minor room was especially reflective, the reverb followed on and when sound was ported in via a speaker. Unfortunately, because the room was so small and full of thick echoes, the room had a mostly uneven timbre. Luckily, people like original, vibey stuff.
    And thus, the Chamber reverb was born.

    Plate reverberators




    There are some exciting qualities to plate reverb. A sheet of metal is a two-dimensional space and three-dimensional space; there are separate echoes at the front of the reverb tail and as the reverb tails out the echo density rises. In a two-dimensional sheet, the echoes are of a similar density from the start of reverberation to the end. Because the speed of sound is much quicker in metal than air, plates have a greater “echo” density. These two factors are what give plates their mark “smooth” reverb tails. Lastly, the higher frequency tones exhaust their energy much faster than lesser tones, while lesser tones actually take more time to build up. This makes the effect of higher frequencies living at the front of the reverb tail while lower frequencies tail out later on. In simple words: metal doesn’t just look shiny, it also sounds shiny

    Spring reverberators

    Spring reverb method uses a transducer at one end of a spring and a pickup at the other end, alike to those used in plate reverbs, to make and capture vibrations within a metal spring. Laurens Hammond has decided a patent on a spring-based motorized reverberation system in 1939. The Hammond Organ comprised a built-in spring reverberator.

    Spring reverberators were once extensively used in semi-professional recording and are often incorporated into Guitar amps due to their uncertain cost and small size. A musical group using spring reverb components by rocking them too and for, generating a thundering, crashing sound produced by the springs colliding with each other.

    Digital reverberators

    Digital reverberators use several signal processing algorithms in order to generate the reverb effect. Since reverberation is mostly caused by a simple reverberation algorithm and a very big number of echoes use some feedback delay circuits to generate a large, decaying sequence of echoes. More innovative digital reverb generators can simulate the frequency and time domain comeback of a specific room (using room sizes, absorption, and other characteristics). In a music hall, the direct sound always reaches at the listener's ear first because it trails the shortest path. Soon after the direct sound, the reverberant sound reaches. The time between the two is known as the "pre-delay."

    Reverberation "reverb," is one of the most generally used audio effects and is often found in synthesizers, guitar pedals, digital audio workstations (DAWs), effects units, and VST plug-ins.

    Advantages of Reverberation


    Reverberations do wonders when it originates to musical symphonies and orchestra rooms when the correct amount of reverberation is present, the sound quality gets improved severely. This is the reason why sound engineers are chosen during the building of these halls.

    Disadvantages of Reverberation


    If a room has roughly nearly no sound absorbing surfaces like roof-wall, and the floor, the sound is expected to bounce back between the surfaces and also it takes a very long time as the sound expires. In such types of room, the listener will then have a problem for registering the orator. This is because he has a habit to hear both the direct sound as well as the repeated and reflected sound waves. And also if these reverberations will be more extreme, the sound is said to run together with a sheer loss of articulation and it develops muddy and also garbled.

    Application of reverberation


    The occurrence of reverberation is exploited by the recorded music or producers of live in order to improve the sound quality. Several systems have been advanced to create and simulate reverberations. Chamber reverberator is one such instance, where the sound is created by a loudspeaker which is then received by a microphone along with other special effects of the reverb. A similar device is a plate reverberator, where a metal plate is used to generate vibrations as an alternative for a loudspeaker.

    How can we reduce reverberations?

    From our remark, we can conclude that, if the surface of the thing in the close enclosed room is covered with sound absorbing substance, the reflected sound will decline much earlier and the listener will so receive only the unique sound. Porous materials like mineral wool and fiberglass are instances of such absorbents. As the sound waves enter mineral wool, sound energy gets transformed to heat through friction.