Reverberation

The phenomenon of sound persistence after it has been stopped as a result of many reflections from surfaces such as furniture, people, air, and other objects within a closed surface is known as reverberation. These reflections accumulate with each reflection and progressively fade away as they are absorbed by the surfaces of the objects in the enclosed space.

This reverberation is similar to an echo, but the distance between the source of the sound and the obstacle through which it is reflected is shorter. The parameter referred to as reverberation time is primarily used to characterise the reverberation quantitatively. The length of time it takes for sound to decay by around 60 dB from its initial level is known as reverberation time. The time delay in the reverberation process is said to be less than 0.1 second, implying that the reflected form of the wave reaches the observer in more or less than 0.1 second. As a result, the time between hearing the reflected sound and hearing the original sound is considered to be very short, and the original sound will still be in the memory when the reflected sound is heard.

Reverberation time

The time it takes for sound to “fade away” in an enclosed space after the source of the sound has stopped is known as reverberation time. The term T60(an abbreviation for reverberation time 60 dB) is used when precisely measuring reverberation time using a metre. T60 is a device that measures reverberation time objectively. It’s the amount of time it takes for the sound pressure level to drop by 60 decibels when the generated test signal is abruptly terminated.

When measured as a wideband signal, reverberation time is typically presented as a single value (20 Hz to 20 kHz). It can be more clearly stated in terms of frequency bands (one octave, 1/3 octave, 1/6 octave, etc.) due to the fact that it is frequency-dependent. Because reverberation time in narrow bands is frequency dependent, the reverberation time will vary based on the frequency band being measured. It’s crucial to understand what frequency bands a reverberation time measurement describes for precision.

Wallace Clement Sabine began studies at Harvard University in the late 1800s to examine the effect of absorption on reverberation time. He measured the time from interruption of the source to inaudibility using a portable wind chest and organ pipes as a sound source, a timer, and his hearing (a difference of roughly 60dB). He discovered that reverberation duration is related to the size of the room and inversely proportional to the quantity of absorption.

The appropriate reverberation duration for a music-playing area is determined by the sort of music that will be performed there. Speaking rooms often require a shorter reverberation period so that speech may be properly understood. It may be difficult to understand what was spoken if the reflected sound from one word is still heard when the next syllable is pronounced.If the reverberation duration is too short, however, tonal balance and loudness may be compromised. Reverberation effects are commonly employed in studios to give sounds more depth. The perceived spectral structure of a sound is altered by reverberation, while the pitch remains unchanged.

The size and shape of the enclosure, as well as the materials employed in its construction, are all basic elements that influence the reverberation duration of a space. This reverberation time can be affected by any object placed within the enclosure, including humans and their belongings.

How to calculate reverberation time

A good technique to identify a noise control problem is to measure the reverberation time of a place. You may have a reverberation problem if your huge open space is plagued by echo and difficulties comprehending conversation. We’ll go over how to figure out the reverberation time for your multi-purpose area in this article.

Advantages of reverberation

When it comes to musical symphonies and symphony halls, reverberation works wonders; when the correct amount of reverberation is present, the sound quality improves dramatically. This is why sound engineers are hired to work on these venues while they are being built.

Disadvantages of reverberation

The sound is said to bounce back between the surfaces if a room has almost no sound-absorbing surfaces such as walls, roofs, and floors, and it takes a long time for the sound to die. The listener will have difficulty registering the speaker in such a room. This is due to his proclivity for hearing both direct and reflected sound waves. Also, if the reverberations are too strong, the sound is said to blend together with a simple loss of articulation, becoming muddy and garbled.

Application of reverberation

Producers of live or recorded music take advantage of the reverberation phenomena to improve sound quality. To make and imitate reverberations, several systems have been devised. A chamber reverberator is an example of this, in which the sound is produced by a loudspeaker and then picked up by a microphone, along with other reverberation effects. A plate reverberator, which uses a metal plate instead of a loudspeaker to produce vibrations, is a similar device.

How can reverberation be reduced?

Based on our observations, the reflected sound will diminish considerably faster if the surface of the items in the neighbouring enclosed space is coated with sound-absorbing material, and the listener will only hear the original sound. Porous materials that can be utilised as absorbents include mineral wool and fibreglass. As sound waves move through mineral wool, friction converts sound energy to heat.

Conclusion

MESSL, a novel probabilistic approach for distinguishing the voice of multiple simultaneous speakers from a stereo mixture, was introduced in this paper. It is based on a top-down multi-source localization system that is versatile and generalises other techniques published in the literature. The separation system alternates between re-estimating the parameters for each source from observations weighted by these masks and constructing a probabilistic time-frequency mask for each source based on its model.

It is possible to find sound sources in space from a genuine binaural recording, which is one of the work’s four goals. In certain circumstances, it is able to isolate the sources sufficiently to determine what is said. It also collects data on early echoes and spectrogram regions dominated by reverberation, which can be used to define the room where the recordings were taken. In both anechoic and reverberant circumstances, the performance of the systems described here is equivalent to that of humans. In anechoic mixtures, MESSL’s separation performance is comparable to humans’, but in reverberation, it only accounts for 20–25 percent of the difference between automatic speech recognition on raw mixtures and human performance.

 While MESSL is able to reject enough of the direct-path component of the masking source in reverberant mixtures to improve energy-based signal-to-noise ratio results, it has trouble rejecting enough reverberation to considerably improve automatic speech recognition results. Other similar separation systems have the same issue.