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MOS score
Home » MOS Score

MOS Score

posted on April 18, 2022

Mean Opinion Scores (or “MOS” scores) are a way to measure the quality of audio, such as the quality of audio in telephone calls. MOS scores have been used for years as a way to standardize the answer to the question: “How was the quality of the phone call?”

Think about it — if you ask ten different people how the quality of a phone call was, you will probably get a number of different answers (like, “it was ok”, “not bad”, “good”, “fine”). These types of answers are not standardized and are not very helpful to really get a feel for how good (or bad) a phone call was.

MOS scores standardize this and provide both objective and subjective measures to normalize how we look at the quality of a call.

Mean opinion scores are a term that is defined in an International Telecommunications Union (“ITU”) standard (ITU-T P.10) as “The mean of opinion scores” or “the value on a predefined scale that a subject assigns to his opinion of the performance of the telephone transmission system used either for conversation or for listening to spoken material.”

While MOS scores were designed to be used in “old school” voice networks, it has been extended for use with SIP and VOIP infrastructure. The specifications set forth various calculations depending on the voice technology used (and depending on what codec is used if SIP / VOIP is the communications protocol used).

In general, the calculated score represents a level of quality from “poor” to “best” (and is generally represented by a numeric such as 4.4 (for a call of “best” quality”) or 2.9 (for a call of “poor” quality).

You can read more about the actual calculation of MOS scores here, but in general, most PBX and ACD systems automatically calculate the MOS scores for calls. For example, the FreePBX switch (based on freeSWITCH) publishes the MOS score for each call in the Call Detail Record (CDR) (see here).


Related Definitions:

  1. Abandoned Calls Abandoned calls are calls that were answered by the phone system (such as the ACD) but never reached a call center agent because the caller either hung up (usually due to a long wait), the caller was interrupted, or the caller realized he/she misdialed and arrived at the wrong number. A high number of abandoned calls can […]…
  2. Call Quality Score Call quality has a subjective component (how did the call quality seem to the agent or to the customer?) as well as an objective component (how well did the measured call attributes score?) The objective aspect of call quality is typically measured using the mean opinion score (“MOS” score). MOS scores have been used to […]…

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