For the sake of simplicity, Noise, sound and everything in its quantification is just in decibels (pascals), a scalar quantity that depicts the sound pressure value. What one makes out of these values in terms of its acceptance is the objective assessment of a product's noise; which roughly can be translated as a type of a PASS / FAIL criteria.
If objective numbers are all that qualifies the noise and its appreciation, there will be no other dimension or appropriation left to define why there are different perceptions of noise or sound, even if both have the same sound pressure values.
This makes one to think that the composition of frequencies and their timing, the spatial effects of sound, modulations, tone, pitch, loudness and many more such subjective factors must be contributing to the sound to be heard in a specific way, finally to be appraised by the listener and call it good or bad for hearing; this subjective assessment of noise is called the quality of sound and the practice called sound quality analysis.
None of the standards or statutory norms that prescribe limits on noise levels mention anything of sound quality; however, the appreciation of sound for its better perception is well considered increasingly in product design and manufacturing space, more as a value addition that leads to better sales.
Binaural head with setup for sound quality assessment
Sound quality assessment procedure includes constituting a team of jury members to listen the sounds, creating time files of audio stacks of the products to be compared and playing the sound files in typical sequence. The Jury members, either sitting in a single physical space or at distributed locations anywhere in the world will listen to the sounds played to them, register their perception and enumerate their observations in a subjective matrix table.
Subjective Matrix to consider for sound quality analysis
Depending on the overall representation of the jury opinion, the subjective matrix is evaluated to arrive at statistically repetitive perception of the played sounds, determine which of the contents in the played sounds relate to the definitions of the objective sound matrix. The iterative loop of updating the objective sound quality matrix from the jury based listener assessment is a continuous process and over the years many new matrix values have been derived and put to use.
Typical sound quality assessment loop
Some of the much known deterministic sound quality terminologies are Loudness, sharpness, tonality, Speech Interference Level, Articulation Index, pitch, squeak etc. All these are derived from understanding the behavior of sound based on subjective evaluations; various filters are created and applied to realize the subjective characteristics to be accounted into objective matrix, thereby updating the sound quality assessment tool package.
NV Dynamics uses the industry acclaimed SEIMENS simcenter sound quality tools across many applications ranging from automotive sub-systems to PA systems to high end audio products in evaluating their performance. The experience of such testing have brought us to develop some of our own filter codes for specific applications. Get in touch to know more.