Enhanced Voice Services (EVS) is a superwideband speech audio coding standard that was developed for VoLTE. It offers up to 20 kHz audio bandwidth and has high robustness to delay jitter and packet losses due to its channel aware coding and improved packet loss concealment. 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.
Work on EVS was started in 2007. The standardization process lasted from 2010 to 2014, being completed in December 2014 with 3GPP Release 12. The codec was developed collaboratively among chipset, handset and infrastructure manufacturers as well as operators and technology providers.
The six patent holders are Fraunhofer IIS, JVC Kenwood, Nippon Telegraph and Telephone, NTT Docomo, Panasonic, and Ericsson. Other contributors included Huawei, Nokia, Orange, Qualcomm, Samsung Electronics, VoiceAge, and ZTE Corporation. A patent pool for EVS has been listed by MPEG LA.
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.
The following features are present in EVS:
- source-controlled variable bit-rate (SC-VBR)
- voice/sound activity detector (VAD)
- comfort noise generation (CNG)
- error concealment (EC) for packet loss in networks
- channel-aware mode to improve frame/packet error resilience
- jitter buffer management (JBM)
Input sampling rates for EVS can be 8, 16, 32, and 48 kHz. It supports the following bitrates (in kbps) for different bandwidths:
- Narrowband (NB): 5.9, 7.2, 8, 9.6, 13.2, 16.4, 24.4
- Wideband (WB): 5.9, 7.2, 8, 9.6, 13.2, 13.2 channel-aware, 16.4, 24.4, 32, 48, 64, 96, 128 (6.6 ~ 23.85 for AMR-WB IO)
- Super-wideband (SWB): 9.6, 13.2, 13.2 channel-aware, 16.4, 24.4, 32, 48, 64, 96, 128
- Fullband (FB): 16.4, 24.4, 32, 48, 64, 96, 128
Bitrates can be switched every 20 ms.
Currently there are about 200 models from different smartphones manufacturers supporting EVS, including:
- 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): 5713–5717. doi:10.1109/ICASSP.2015.7179066. ISBN 978-1-4673-6997-8.
- 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): 5708–5712. doi:10.1109/ICASSP.2015.7179065. ISBN 978-1-4673-6997-8.
- The 3GPP Enhanced Voice Services (EVS) codec. Nokia white paper.
- Enhanced Voice Services (EVS) Codec. Fraunhofer Technical Paper, 2015
- "HD Voice". Future Networks. Retrieved 2020-05-10.
- "Licensors Included in the EVS Patent Portfolio License". MPEG LA. Retrieved 10 July 2019.
- MPEG LA Facilitating Development of Enhanced Voice Services Patent Pool License. MPEG LA News Release, 20.01.2016
- Järvinen, Kari. "Enhanced Voice Services Codec for LTE". 3GPP.
- "EVS". Fraunhofer Institute for Integrated Circuits IIS. Retrieved 2020-05-10.
- "VoiceAge EVS". voiceageevs.com.