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HE-AAC – the sound for both TV and mobile

Like NICAM before it, HE-AAC sound is an almost secret service that supports and enhances vision formats. As high definition distribution continues to grow, the Advanced Audio Coding format family is becoming a key part of streaming services as well as broadcast.

Technology has always been a boundary breaker but these days it is not just lowering the barriers but bringing closer together areas that were once seen as very different and separate from each other. Broadcast television and domestic video and audio systems are classic examples; until recently broadcasting stood apart from the consumer sector but now the two are based on similar, if not the same, technological formats.

This was neatly illustrated during IBC 2012 on the Fraunhofer IIS (Institute for Integrated Circuits) Audio and Multimedia stand. A conventional home broadcast set-up of flat screen television and surround sound box receiving digital terrestrial TV (DTT) signals on one side of the booth was matched on the other by a demonstration of HD video on a big monitor with 5.1 (pictured).

In this case the source was a mobile phone but most people would have to look and listen very hard to detect any differences. The demonstration highlighted Fraunhofer IIS’s work with Android, getting the AAC (Advanced Audio Coding) codec into version 4.1 (Jelly Bean) of the handheld operating system. Fraunhofer IIS’s Matthias Rose said all Android 4.1 devices now feature these audio codecs and include HE-AAC (High Efficiency Advanced Audio Coding): “We are showing here that you can plug in your mobile phone with a home theatre system and play-back 5.1 surround sound in the highest audio quality just by using a mobile device.”

Multi-channel HE-AAC is supported natively in Android 4.1, with 5.1 surround reproduction on phones and tablets equipped with the OS. By using a HDMI (High Definition Multimedia Interface) link the output of the phone can be played out through home cinema systems, in conjunction with video streaming technologies including MPEG-DASH (Dynamic Adaptive Streaming over HTTP). Known informally as DASH, this new technology streams live broadcasts from the web by switching between bit rates to ensure the highest bandwidth for the best possible quality.

The audio performance of HE-AAC for Android 4.1 is compared to that of Blu-ray Disc and DVD. It did not sound substantially different to what was coming out of the DTT set-up and was a lot more consistent and impressive than the picture, which sometimes appeared blocky.

Robert Bleidt, division general manager of Fraunhofer USA Digital Media Technologies, observed, “With the inclusion of HE-AAC multichannel in Android 4.1, users will be able to enjoy full surround sound with content delivered to Android phones and tablets as easily as they have with Blu-ray or DVD titles. Connecting a HDMI cable from their existing audio/video receiver or TV set to the MHL or HDMI connector on Android devices will deliver foolproof surround audio and video.”

Rose said the IBC display was to show that AAC codecs, including HE-AAC and MPEG Surround, were “a perfect fit for MPEG-DASH because they can be used exactly the way it [DASH] is designed for seamless playback and switching of audio and video”. He added that having seamless switching, with no drop-out, was important for DASH, which is based on the concept of changing bit rates to adapt to the bandwidth dynamically to what is available.

HE-AAC is also used in the operating systems of Mac OS X and Windows and mobile formats including iOS, Windows Phone, Symbian and BlackBerry, as well as Android 4.1. In today’s seemingly mobile obsessed world it would be easy to overlook that the same technology is also used in the broadcast TV chain, with the majority of HD-ready sets on the market today supporting it.

Rose commented that Fraunhofer was keen to show that HE-AAC had a life beyond computers and was part of general broadcasting. DVB-T2, the second generation of the DTT distribution standard, is now being used across Europe for HD transmissions and includes HE-AAC as an audio format. HE-AAC fully supports all broadcast relevant metadata and any channel configuration from mono to up to 48 channels, including stereo and 5.1 surround.

Matthias Rose said the more familiar TV demo during IBC was to show that HE-AAC was for broadcast as well as streamed services but acknowledged that it still had a very low profile. “This codec is really dominating the world of streaming and broadcasting these days,” he concluded. “But it is what you might call a hidden champion.”