Sound Quality essentially refers to the content and time based composition of frequency contents in a given noise signal and the human perception to like or dislike it.

Noise or Sound as perceived by human is a change in the pressure gradient of medium involved. This means that the medium shall be elastic in nature to allow the compression and rarefaction of the pressure wave.

For all the objective quantification, we invariably use sound pressure levels as the base quantity and represent them in dB, dBA and so on. Given the human ear's response to various frequencies, the attenuation and amplifications happens and thus the final perceived noise is some kind of filtered net quantity.

A combination of frequencies, their predominance and time sequencing in the given noise signal makes each type of noise to sound differently and hence their perception. Many classifications of such permutations are made and are given names such as loudness, harshness, tonality, squeak, roughness, Articulation Index, Speech Interference Level and many more.

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However, since any noise generating source, based on its physical configuration, operation and other governing factors, can generate a variety of sound patterns, many a times it becomes essential to 'feel or listen to' the sound than just quantifying it by numbers. The whole methodology of understanding the noise by its perception and then linking them to the objective values of sound matrix (load, harsh, tonal etc) is called the sound quality analysis.

Sound quality assessment is best used when evaluating two or more similar types of noise sources. For example, it can be used to evaluate engines of similar make and model or for comparing the characteristics of a noise generating equipment which is in use over a certain period of time versus a brand new equipment, etc.

Sound quality engineering has many surprises to reveal, some of the assessed products tend to give lower sound pressure levels but end up in lower user appreciation due to the way it registers in terms of its frequency contents, thus the sound quality someway is a representative of product quality and can influence buying decision.

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As for the methodology of sound quality assessment goes, there are very good tools and applications that help in evaluating the subjective matrix sound perception. The process involves gathering noise time data, applying series of filters and running them through a process called "jury testing", once done with the procedure, a number of outputs are putout on how people from various backgrounds and social exposures appreciate the sound and its perception.

The end goal of sound quality process is to connect the subjective evaluation of sound to the objective sound matrix and update the qualification process accordingly.

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