Fraunhofer Institute for Integrated Circuits IISThe LC3 and LC3plus audio codecs were developed in order to solve essential shortcomings present in today’s wireless communication platforms such as Bluetooth and Digital Enhanced Cordless Telecommunications (DECT). The codecs’ operation modes range from medium bit rates for optimal voice transmission up to high bit rates for high-resolution music streaming services (the latter applies to LC3plus). At the same time, the codecs operate at low latency, low computational complexity and low memory footprint.
LC3/LC3plus
Challenges
The introduction of the 3GPP Enhanced Voice Services (EVS) audio codec for VoLTE brought super wideband (SWB) audio quality to mobile phones, making users feel as if they were in the same room as their conversation partners. However, it has not been possible to date to deliver this high audio quality if a mobile phone user calls someone who is using a DECT telephone or a wireless headset.
On the audio side, the recently launched high-resolution music streaming services offer a novel listening experience with transparent audio quality. But so far, there has been no open standard to transmit this high audio quality over a wireless link, for example, to wireless headphones or speakers.
The challenge of connecting these services to other wireless communication platforms and accessories had to take into account different requirements with regards to computational complexity, latency, and memory demands. The result is the Low Complexity Communication Codec LC3 and its sibling LC3plus, which Fraunhofer IIS and Ericsson jointly developed in order to bring super wideband phone calls to platforms such as Bluetooth, VoIP or DECT, as well as enabling high-quality audio streaming on wireless headsets or speakers.
Our solution
LC3 and LC3plus extend high audio quality to the entire communication ecosystem. The codec’s complexity meets the requirements of wireless communication platforms such as Bluetooth, DECT, and VoIP terminal equipment. By reducing the required bit rate by roughly 50 percent compared to legacy codecs, LC3 and LC3plus facilitate low-energy services that enable a longer battery life or the creation of smaller products. Due to the flexible codec design, applications are not limited to voice services but can be extended to high-quality music streaming as well.
LC3plus is the standardized solution to provide the quality of high-resolution music streaming services also over wireless accessories – facilitating independence from proprietary, vendor-specific technologies.
LC3
With LC3, it will become possible to enjoy EVS speech quality in VoLTE calls also via Bluetooth headsets. Moreover, it takes the music streaming experience on wireless accessories to the next level. The LC3 specification has been adopted by Bluetooth SIG and LC3 has been selected as the new codec for Bluetooth Low Energy (LE) Audio. In parallel, integration work into the legacy Hands-Free Profile has started.
LC3plus
LC3plus is LC3's sibling, equipped with numerous additional functionalities. While comprising all features of LC3, including high speech and audio quality, LC3plus incorporates functionalities for transmission robustness, extremely low-delay use cases and high-resolution audio transmission. To improve robustness, LC3plus contains a very high-performance packet loss concealment algorithm as well as forward error correction schemes such as channel coding or redundancy frame modes. Furthermore, the codec can operate at several low-delay modes – down to 5ms at a 2.5ms packet size, instead of the 7.5 ms frame length mode known from LC3. LC3plus also includes dedicated high-resolution audio modes, which improve the measurable audio quality to provide perceptual transparency (up to 500 kbit/s per channel).
LC3plus is the equivalent to EVS for landlines and enables super wideband quality for VoIP use cases, while the number of channels stays the same as in wideband. Redundancy frame modes permit the transmission of LC3plus payloads over congested VoIP channels, enabling stable phone calls even under these conditions.
LC3plus has been standardized by ETSI as TS 103 634 and brings super wideband speech/audio quality to DECT thanks to its adoption into the 2019 DECT standard. For wideband, the capacity doubles compared to the preceding standard. In terms of robustness, LC3plus’s channel coding, which was specifically designed for DECT channel characteristics, permits the transmission of LC3plus payloads over heavily distorted DECT channels – enabling phone calls without interruption, even if the handset is far away from the base station.
LC3plus’s dedicated high-resolution audio mode provides a high-quality transmission link of 24 bit and 96 kHz audio data, which performs excellently with regards to Signal-to-Noise Ratio (SNR) and Total Harmonic Distortion and Noise (THD+N). This makes it the ideal codec to bring high-transparency audio streaming to high-resolution wireless accessories such as headsets or loudspeakers. LC3plus is the only open-standard audio codec for high-resolution wireless headsets and high-quality gaming headsets. Fraunhofer IIS can provide support with the implementation of LC3plus in devices based on the Bluetooth A2DP profile.
Implementing LC3plus High-Resolution as the codec of choice for wireless transmission opens the door for device manufacturers to receiving the valuable logo from the Japanese Audio Society (JAS). Following an extensive objective and subjective testing process, it recently certified LC3plus High-Resolution and included it in the list of certified codecs. This shows that LC3plus High-Resolution meets the criteria set by JAS, in particular the support of a 96 kHz sampling rate, at least 24 bits per audio sample, and the ability to reproduce frequencies of 40 kHz and above.
Hi-Res Audio Wireless Logo of JAS.
Availability
LC3
The Bluetooth specification is available here
LC3 software for Bluetooth is available through Fraunhofer. Additionally, Fraunhofer IIS offers software and licenses for Advanced Packet Loss Concealment as an add-on to the Bluetooth-standardized LC3.
LC3plus
LC3plus software is available from ETSI
ETSI TS 103634: A detailed description of the LC3plus algorithm is available here
Also, Fraunhofer IIS can provide support with the implementation of LC3plus HR in the Bluetooth A2DP profile. On our website, we offer a specification for use as vendor specific codec via Bluetooth A2DP and upon request, we offer Android patches for LC3plus HR via Bluetooth A2DP.
Patent licensing
Information about LC3/LC3plus patent license is available here.
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