Enhanced Voice Services (EVS) is a superwidebandspeechaudio coding standard that was developed for VoLTE and VoNR. It offers up to 20 kHz audio bandwidth and has high robustness to delay jitter and packet losses due to its channel aware coding[1] and improved packet loss concealment.[2] It has been developed in 3GPP and is described in 3GPP TS 26.441. The application areas of EVS consist of improved telephony and teleconferencing, audiovisual conferencing services, and streaming audio. Source code of both decoder and encoder in ANSI C is available as 3GPP TS 26.442 and is being updated regularly. Samsung uses the term HD+ when doing a call using EVS.
Work on EVS was started in 2007. The standardization process lasted from 2010 to 2014, being completed in December 2014 with 3GPP Release 12.[3] The codec was developed collaboratively among chipset, handset and infrastructure manufacturers as well as operators and technology providers.[4]
GSMA requires EVS for their HD Voice+ Logo Licensing Program.[5]
EVS employs similar concepts to its predecessors, such as AMR-WB, to which it retains backward-compatibility. It switches between speech and audio compression modes depending on the content, using ACELP and MDCT.
Inter-carrier interoperability is a problem, as calls are by default routed over narrowband connections which downgrades the voice to narrowband quality instead of EVS and HD Voice even if the individual phones and carrier networks all support EVS.[11] Thus, users are encouraged to switch from phone calls to pure VoIP apps such as FaceTime, WhatsApp, Signal, Facebook Messenger, and Telegram when voice call quality remains poor despite good network connectivity.[12]
EVS, like AMR-WB and AMR-WB+, incorporates several patents. As with those two codecs, VoiceAge Corporation is in charge of the licensing[13] and offers RAND pricing[14]
^Atti, V.; Sinder, D. J.; Subasingha, S.; Rajendran, V.; Dewasurendra, D.; Chebiyyam, V.; Varga, I.; Krishnan, V.; Schubert, B. (2015-04-01). "Improved error resilience for volte and VoIP with 3GPP EVS channel aware coding". 2015 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP). pp. 5713–5717. doi:10.1109/ICASSP.2015.7179066. ISBN978-1-4673-6997-8. S2CID17443373.
^Lecomte, J.; Vaillancourt, T.; Bruhn, S.; Sung, H.; Peng, K.; Kikuiri, K.; Wang, B.; Subasingha, S.; Faure, J. (2015-04-01). "Packet-loss concealment technology advances in EVS". 2015 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP). pp. 5708–5712. doi:10.1109/ICASSP.2015.7179065. ISBN978-1-4673-6997-8. S2CID11693594.
