Crystal-clear phone calls

© Piotr Banczerowski / Fraunhofer

Joseph von Fraunhofer Prize recipients: (from left to right) Markus Multrus, Dr. Guillaume Fuchs, and Stefan Döhla.

Developers of the EVS codec awarded with the Joseph von Fraunhofer Prize.

There is not much that smartphones can’t do, but one aspect of their performance still leaves a great deal to be desired: voice quality in phone calls. This is set to change with the new Enhanced Voice Services (EVS) standard: instead of sounding muffled and distorted, the voice on the other end of the line will be as clear and natural as in a face-to-face conversation.

EVS is the new communication codec of the 3rd Generation Partnership Project (3GPP), an international standards body for mobile communications. Fraunhofer IIS played a major role in the development, with a research team of more than 50 experts. The Joseph von Fraunhofer Prize was received by Markus Multrus, Dr. Guillaume Fuchs, and Stefan Döhla on behalf of the team.

A standard of this sort has to fulfill rigorous specifications. “First of all, the codec must be capable of transmitting highquality speech signals at relatively low data rates, so as not to compromise cost-efficiency,” says Markus Multrus, who coordinated the software development for the codec at Fraunhofer IIS. Furthermore, the codec must be sufficiently robust to withstand transmission errors. Finally, it must also be able to transmit other signals, such as music, with high sound quality.

»The average human ear can hear frequencies of up to 20 kilohertz,« explains Dr. Guillaume Fuchs, in charge of scientific development for the EVS standard. »The codec currently used for most telephone calls on mobile networks in Germany only transmits audio signals up to 3.4 kilohertz – the range between 3.4 and 20 kilohertz is simply cut off. This makes phone calls sound muffled. The new codec allows frequencies of up to 16 or even 20 kilohertz, depending on the bitrate.« As a result, the entire audible frequency spectrum is transmitted.

Before a new codec can be implemented as a standard, it has to pass numerous listening tests involving thousands of test subjects. In these tests, listeners rated EVS as significantly better than previous formats. The new codec has since been approved as a standard by 3GPP, meaning that chip manufacturers can implement it in mobile phone application processors and device manufacturers can integrate it into new products. “EVS is already in commercial use in a number of countries including Germany, Japan, the Netherlands, Austria, Poland, South Korea, the UK, and the US,” says Stefan Döhla, who represents Fraunhofer IIS at 3GPP.