How to measure Quality

> What do we really hear?
"Clearly to achieve an estimate of the perceived quality, a measurement should employ as much of an understanding of human perception as possible."

Transmission errors, noise, distortion and losses due to low bit-rate coding and packet transmission – These are all parameters you can measure. But just how do they relate to human perception?

If you perform measurements, most likely you are aware of the limits of conventional testing when it comes to digital compression quality. Clearly to achieve an estimate of the perceived quality, a measurement should employ as much of an understanding of human perception and human judgement as possible.
> OPTICOM and the introduction of perceptual measurement Perceptual measurement is still in its infancy, but has been the core focus of OPTICOM since 1995. A track record of almost 20 years of research and development and the introduction of International Standards has contributed to the clear leadership at the forefront of technology of objective audio quality assessment. If you are dealing with telecommunication, multimedia and broadcast, you can gain immediate advantage of our latest diagnostic techniques to quantify your customer's speech and audio quality perception.

Our directory of references includes leading R&D institutions, universities, manufacturers of telco and audio equipment, operators and broadcasters worldwide.

> Technologies for Voice Quality Testing
POLQA, Perceptual Objective Listening Quality Analysis (FR) according to ITU-T Rec. P.863 [2011]. The Next-Generation Mobile Voice Quality Testing Standard for HD-Voice, VoIP, 3G and 4G/LTE
PESQ, Perceptual Evaluation of Speech Quality (intrusive) according to ITU-T rec. P.862 [2001]. Combines PSQM with PAMS, optimized for VoIP and hybrid end-to-end applications
P.563, perceptual single-sided speech quality measure (non-intrusive) according to ITU-T rec. P.563 [2004]
Echo measurement based on real speech, Echo Return Loss ERLmom, ERLpeak, ERL vs. delay
> Technologies for Audio Quality Testing

PEAQ, perceptual evaluation of audio quality according to ITU-R rec. BS.1387 [1999], Basic and Advanced Model

> How it works... The common idea behind perceptual quality measures is to mimic the situation of a subjective test, where human beings would have to score the quality of sound samples in a listening laboratory environment. The result is called 'mean opinion score', MOS. During a long time, subjective test procedures were the only means of assessing the sound quality impression. Of course, subjective experiments require a huge number of subjects to achieve statistically relevant results, and thus are very costly and time consuming. For quality testing in the laboratory as well as in the field, subjective tests are clearly not an option. Consequently, perceptual models can be applied to generate an objectively derived quality metrics ('objective MOS' or OMOS) that can be compared to a mean opinion score scale. In the course of perceptual processing, many other detailed model output values, such as FFT spectra, dynamically measured bandwidth, distortions, modulation and excitation will be generated and reported, too, making this technology universally applicable.

> Further information The state-of-the-art technology for subjective and objective testing is compared under ' Fundamentals of perceptual modeling ' , for information on algorithms you may click on the above links, or proceed with 'Voice Quality' or 'Audio Quality'. References to literature and standards documents, also for download, are also provided under this section 'Technology'. To view our range of OPERA products incorporating the technology described herein, go to our 'Products and Services' section.