xHE-AAC : The combination of Extended HE-AAC and MPEG-D DRC

xHE-AAC for DRM

DRM (Digital Radio Mondiale) is the first digital radio standard to adopt xHE-AAC (mandatory since 2013) and benefit from its features. As xHE-AAC is a superset of the MPEG HE‑AAC codec used for all DRM transmissions to date, HE‑AAC remains available as part of the DRM standard to retain compatibility with existing systems. With xHE-AAC, DRM broadcasters can now use the same codec for all types of content and benefit from a simplified codec configuration process: The encoder automatically optimizes all quality-relevant parameters, eliminating the need to change configuration settings depending on the type of audio content being broadcast. In addition, the reduced bit demand of the codec allows for the delivery of a wider selection of audio programs.  

xHE-AAC (the combination of Extended HE-AAC and MPEG-D DRC), primarily developed by Fraunhofer IIS and the latest addition to the MPEG AAC codec family, bridges the gap between speech and audio coding. It provides consistently high-quality audio for all signal types, such as speech, music or mixed content, at all bit rates – starting as low as 6 kbit/s for mono and 12 kbit/s for stereo services, up to 500 kbit/s and above. This makes xHE-AAC the audio codec of choice for digital radio and adaptive streaming applications. It is a mandatory audio codec in Digital Radio Mondiale (DRM) and in Google's Android Pie operating system; the FDK2 implementation including xHE-AAC is provided by Fraunhofer and is available here.

Adaptive Streaming

xHE-AAC was inherently designed for adaptive streaming: its bit rate flexibility enables MPEG-DASH or HLS streaming apps and streaming radio players to switch to very low bit rate streams and offer continuous playback even under challenging network conditions. When network connectivity recovers, the xHE-AAC player will adapt to a higher bit rate and seamlessly switch over the full range of bit rates, up to transparent quality. Additionally, the outstanding coding efficiency of xHE-AAC means the bit rate saving can be invested in improving the video quality of mobile video streaming.

Loudness and Dynamic Range Control

MPEG-D DRC – Loudness and Dynamic Range Control – provides mandatory loudness control for xHE-AAC to play back content at a consistent volume and offers dynamic range control processing to provide the best possible user experience for listening on any platform and in any environment.

Compatibility of xHE-AAC

xHE-AAC profile decoders are capable of decoding all AAC versions including AAC-LC, HE-AAC and HE-AACv2. It is easy to integrate xHE-AAC streams into existing encoding workflows by supplementing legacy higher bit rate streams.

Source: Fraunhofer.

For details click the link below.

https://www.iis.fraunhofer.de/en/ff/amm/broadcast-streaming/xheaac.html