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5 Basics To Understand Mean Opinion Score

Mean opinion score (MOS) is becoming a standard indicator to perceive media quality. While it has been used extensively in speech quality, it is also being deployed in other modalities.

It includes audio, images, video, and audiovisual content. In various, from lab testing to in-service monitoring, MOS has emerged as a popular factor to quantify media quality. MOS can be both subjective and objective. Objective speech quality assessment helps to replace the time-consuming and cumbersome subjective listening test.

Application Areas Of MOS

MOS is mainly used in the domain of Quality of Experience and telecommunications engineering. It is a  commonly-used metric to measure the overall quality of a stimulus or system. MOS helps to gauge the voice quality and clarity of the communication. The various practical applications and uses of MOS scores can be grouped into three major groups. The application areas generally include quality monitoring, fault isolation, and service level agreements.

  • Quality Monitoring And Alerts: It notifies users about the potential issues, and MOS is well-suited. It is because MOS is representative of overall quality and helps to gauge the various problems in service. The MOS value is typically generated for small content segments. Hence, it also makes it possible to identify the short-term fluctuations in quality. MOS helps in measuring the satisfaction and acceptance of service. They are meaningful units for quality monitoring.
  • Fault Isolation: MOS methods help in evaluating individual quality dimensions. The MOS score provides a reference point for gauging the audio or video quality in a subjective test. However, it is not merely enough to establish the existence of an issue; one needs to identify its root cause to fix it. With additional measurements, MOS can help identify the grounds of a problem. It facilitates the understanding and measurement of impairments on quality.
  • Service Level Agreements: A service-level agreement functions as a commitment between a service provider and a client. A service provider can use the MOS score to offer or maintain quality-based SLAs to differentiate pricing plans according to quality levels. It helps to compare service quality with the competition. MOS is a popular measure of media quality.

Quality Levels Of MOS Score

MOS is defined as a numeric value that typically ranges from 1 to 5. The ascribed MOS score corresponds to the arithmetic mean of individual ratings for a given user panel. MOS is an excellent measure of the Quality of Experience (QoE). A score of 3.5 and higher is essential for high-quality service. MOS helps to measure and evaluate video, audio, and audiovisual quality. The call quality dashboard makes use of MOS as the primary measurement to report on voice quality. Each device in a call has an inbound MOS and an outbound MOS. The inbound MOS indicates the score of incoming audio and helps determine if you can hear the person on the other side over background distractions or a poor network connection. The outbound MOS indicates a score for outgoing audio or video to gauge how others can hear you over background noise or a slow network. A MOS greater than or equal to 3.5 shows that the call quality is good, whereas below 3.5 means poor quality.

  • MOS score of 5 indicates excellent quality, with imperceptible impairment. The user does not have to put effort into understanding the language.
  • MOS score of 4 indicates good quality, with perceptible impairment. It requires attentive listening, but one does not need to put any effort into listening.
  • MOS score of 3 indicates acceptable quality, with annoying impairment. You can hear speech with a bit of effort.
  • MOS score of 2 indicates poor quality, with very annoying impairment. It requires more significant concentration and effort to understand the transmitted language.
  • A MOS score of 1 indicates bad quality, and communication is impossible.

Factors Affecting MOS Score

The MOS score is measured on a relative scale and encompasses various factors that can affect service quality. It may include bandwidth, codec in use, hardware, jitter, latency, and packet loss.

  • The Codec version is a critical factor that can significantly impact the MOS score. Different codecs are available for voice transmission. Each codec generates a particular data stream, which results in the generation of a specific MOS score.
  • A jitter buffer includes a domain where voice packets are collected and stored. It is then sent to a processor at certain intervals, which can delay packages, which gives clarity and less distortion to the voice transfer. Jitter measures the time difference in packet inter-arrival time.
  • Packet Loss refers to the failure to transmit data packets to reach their destination across a network.
  • Hardware that you use within your network and the VoIP hardware can also affect the MOS score.
  • The internal network bandwidth and your external bandwidth impact the MOS score.

Calculating MOS

The automated test equipment is being leveraged to calculate MOS using sophisticated algorithms. It helps to approximate the subjective listening test results closely. The MOS aggregates various speech impairments into a single score. The use of IP and analog measurements helps to match a real caller’s perception of speech quality. The algorithms which use actual speech for calculating MOS may use a human caller, IVR, or human system as a test source.

When calculating MOS manually, you subject a group of people to serve as test subjects and place a communications system in a sound-proof room. Test subjects will enter the room one at a time to rate voice quality. The use of live listeners can prove to be costly and time-consuming. It is increasingly being replaced by automated solutions to rate more rapidly and accurately.

Different MOS Metrics

  • Listening MOS forecasts wideband Listening Quality (MOS-LQ) of the concerned audio stream. It considers audio fidelity, consistency, and distortion. It helps in predicting how the user group will rate audio quality.
  • Sending MOS forecasts the wideband MOS-LQ of the audio stream that the user sends. It considers the user’s speech and noise levels and the distortions. It helps to predict how the user group will classify audio quality.
  • Network MOS forecasts wideband MOS-LQ of the played audio. It considers network factors like codec version, packet loss, and packet errors.
  • Conversational MOS forecasts narrowband Conversational Quality (MOS-CQ) of the played audio stream. It considers the audio’s quality sent across the network, speech and noise levels, and echoes for both users involved. It helps to identify audio quality during a conversation.

To Conclude

MOS score is a subjective benchmarking method to measure audio or video service quality. Taking the MOS score into consideration can help you provide the best service quality to keep your end-users happy.

Originally posted 2021-09-29 06:09:32. Republished by Blog Post Promoter

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