Quality and Usability

Speech Quality per Call

Modeling overall speech quality in telephone conversations

Motivation & Project Description

  • Speech quality of mobile telephone or VoIP networks varies with time due to changes in transmission channel characteristics.
  • Motivation: In order to plan and monitor telephone networks with time-varying quality, a model has to be established, that can quantify user’s final judgments immediately after finishing a call.
    • Experiments have been conducted to obtain quality ratings “per call” and those of short-term speech samples.
    • A model was developed, that incorporates the results of the experiments.
    • The model was evaluated with independent rating experiments.


  • The model successfully predicts quality “per call” out of short-term quality estimates obtained by an instrumental method.
  • Standardization: The method was approved by the ETSI STQ mobile group (TR 102 506).
  • Scientific publications

Time Frame: 01/2007 - 04/2007

T-labs Team Members:S. Möller, B. Weiss

Partners: SwissQual AG, Solothurn, Switzerland
Ericsson L.M., Sweden

Funding by:

  • T-Mobile, Germany
  • E-Plus, Germany