Pertaining to the quality or other aspects of the machine that might be inferred from the sound it makes.
- Sound Quality Metrics
- There are a number of pro's and con's with the whole subject of metrics. The psychoacoustics of hearing is a very complicated subject based on the fact that the ear and the processing of sounds is a very complicated subject. Therefore, the simple use of a mathematical expression to give a single number that represents whether one sound is better than another in terms of quality can be an over simplification. Great care should be taken to understand the mathematics and limitations of what the result tells you about the sound. Therefore, an overcheck of listening to the sounds back to back should be carried out as a minimum. Jury evaluation is a better more in-depth approach.
- Articulation Index
- A quantitative measure of the intelligibility of speech; the percentage of speech items correctly perceived and recorded.
- This is the most generally used filter when making overall noise measurements.
- The B-weigthing curve approximately follows the 70 phon curve.
- The ratio, expressed in decibels, of the energy in the first 80 milliseconds of an impulse sound arriving at a listener's position divided by the energy in the sound after 80 milliseconds.
- Crest Factor
- Peak value divided by the R.M.S. value, used as a measure of the severity of a segment of data.
- Effective Perceived Noise Level
- A complex rating used to certify aircraft types for flyover noise. This includes corrections for pure tones and for the duration of the noise.
- A tendency for a distribution to form a sharp narrow peak.
- A subjective term for the sensation of the magnitude of sound.
- Noise Criteria
- Standard spectrum curves by which a given measured noise may be described by a single NC number.
- Noise Pollution Level
- A variation of LAeqT which accounts for short term variability in noise level.
- Sound Exposure Level
- Used to describe the amount of noise from an event such as an individual aircraft flyover.
- Zwicker Loudness
- This is an objective method for measuring noise.
See also: Jury Evaluation.