Voice

Voice Quality Measurement – E Model

The output from the E model is a scalar quality rating value, R, which varies directly with the overall conversational quality.
The model estimates the conversational quality from mouth to ear as perceived by the user at the receive side, both as listener and talker.

R = R0 – Is – Id – Ie-eff + A

R0 represents basic signal-to-noise ratio
Is is a combination of all impairments which occur simultaneous with the voice signal
– Too low values of Overall Loudness Rating
– Non-optimum Sidetone
– Quantizing distortion
Id represents impairments caused by delay
– Talker echo
– Listener echo
– Too long absolute delay

R = R0 – Is – Id – Ie-eff + A
Ie-eff (effective equipment impairment) represents impairments caused by low bit-rate codecs
A (advantage factor) allows for compensation of impairment factors when there are other advantages of access to the user
– Conventional: 0
– Mobility in a building: 5
– Mobility in a geographical area or moving in a vehicle: 10
– Access to hard-to-reach locations: 20

Application of E-Model

“Once the results of planning calculations are available in terms of the E-Model Rating R, a first concern should be for connections where this value is R ≤ 50. Lower values of E-Model Rating R are not recommended, even in exceptional cases. The realization or the practical use of a reference configuration which, with its corresponding parameter values, results in lower R values is not recommended. For such connections, either other solutions should be found or other equipment should be selected in order to increase the end-to-end speech transmission quality to higher values.”

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