Audio Quality Measurement - The Need For Measurement

The Need For Measurement

Measurement allows limits to be set and maintained for equipment and signal paths, and different pieces of equipment to be compared. While the issue of measurement is controversial, to the extent that Hi-Fi magazines these days tend to shun measurement in favor of listening tests, it is important to realize that audio quality measurement has in the past got a bad name by failing to produce results that correlated well with listening tests. This was because certain basic measurements were used, such as THD measurement, and A-weighted noise measurement, without any proper consideration of whether these related to subjective effects. The proper approach to measurement, which is largely adopted by broadcasters and other audio professionals, is to first devise measurements that can quantify the various forms of corruption in terms of subjective annoyance to a human listener, ideally the most critical listener based on tests using many suitably rested subjects. Once this is done, measurement has the advantage of not being dependent on a particular listener, or his/her state of hearing on a given day. It also has the advantage of being able to quantify corruption levels that would not be audible to even the most sensitive ear, which is important because a typical audio path from source to listener can involve many items of equipment, and just listening to each is not a guarantee that they will still sound acceptable when cascaded so that all their deficiencies add up.

A measure for testing audio quality for codecs is also given by the Mean Opinion Score.