Mean Opinion Score
The Mean Opinion Score (MOS) is the arithmetic mean of individual evaluations and can range from 1 (worst value) to 5 (best value).
In telecommunications , the MOS value is mainly used to assess the quality of voice and image transmission services. It is the result of a set sequence of several tests in which the subjectively perceived quality of the language or the images is assessed by a group of test persons. The result of the test series is classified on a five-level quality scale.
MOS quality scale
| value | quality | meaning |
|---|---|---|
| 5 | excellent | No effort is required to understand the language. |
| 4th | Well | By listening carefully, the language can be perceived without effort. |
| 3 | neat | The language can be perceived with easy effort. |
| 2 | moderate | It takes great focus and effort to understand the language being conveyed. |
| 1 | inadequate | Despite a great effort, one cannot communicate. |
With the MOS, the quality of different speech codecs , speech connections, echo cancellers or image compression algorithms can be compared with one another.
The tests that are carried out to determine MOS values for voice transmissions are divided into listening only , conversational and double talk and interview and survey tests . Different quality assessments are carried out, such as B. an absolute quality assessment, quality deterioration, assessment of the effects of certain effects. The tests (for voice transmissions) are specified in the ITU-T in recommendation P.800.
In ITU recommendations P.830 to P.834, subjective evaluation methods for telephone band codecs (300–3400 Hz), broadband codecs (50–7000 Hz), for echo cancellers and for hands-free operation are developed.
MOS values are also used for quality assessments that are carried out on the basis of objective models (which simulate the human subjective perception of quality) and network planning models. This often leads to confusion and misunderstanding.
Therefore, with ITU-T recommendation P.800.1, the following terminology was introduced to differentiate between different types of MOS values:
Differentiation of MOS values
| Listening-only | conversational | talking | |
|---|---|---|---|
| objective | MOS-LQOY | MOS-CQOY | MOS-TQOY |
| subjective | MOS-LQSY | MOS-CQSY | MOS-TQSY |
| estimated | MOS-LQEY | MOS-CQEY | MOS-TQEY |
LQ = listening quality, CQ = conversational quality, TQ = talking quality
S = subjective, O = objective, E = estimated
Y is a placeholder to identify the audio bandwidth under consideration and can have the following values:
- N stands for narrow band (300–3400 Hz)
- W stands for broadband (50-7000 Hz)
- M stands for mixed narrow and broadband tests (with broadband as reference quality)
The following MOS examples show the differences between the various codecs:
| Codec (data rate) | Mean Opinion Score (MOS) |
|---|---|
| AMBE (2.4 kbit / s) ( Iridium ) | 3.3 |
| G.723.1 (5.3 kbit / s) | 3.65 |
| G.729a (8 kbit / s) | 3.7 |
| G.726 (32 kbit / s) | 3.85 |
| G.723.1 (6.3 kbit / s) | 3.9 |
| G.729 (8 kbit / s) | 3.92 |
| G.711 (64 kbit / s) | 4.4 |
| G.722 (64 kbit / s) | 4.5 |
See also
Web links
- P.800 ITU-T recommendation P.800
- Typical mean opinion score values (MOS) ( Memento from March 16, 2007 in the Internet Archive )
Individual evidence
- ↑ ITU-T recommendation P.800.1 P.800.1: Mean opinion score (MOS) terminology ( English ) ITU. Retrieved September 8, 2019.