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Audio for HD and UHD

Sound is one of the most important elements of film and television productions.

Since the invention of the gramophone and radio broadcasting, sound without pictures has become a daily part of people’s lives – from the drive to work, to cooking in the kitchen. Radio has conditioned audiences to appreciate the quality of good sound production. This expectation means that television and film sound has to be high quality. 

Today, high-quality sound processing capabilities are available, which offer impressive dramatic options for the directors, sound designers and, above all, the audience.

Many broadcast channels offer 5.1 surround sound as well as stereo mixes. With UHD -TV, new audio codecs such as MPEG-H and Dolby AC-4 open up completely new possibilities including object-based Next Generation Audio (NGA) and 3D audio.

The advances in audio capabilities from mono to stereo to surround and further to 3D audio is comparable with the trend for ever-higher image resolutions and larger screen sizes. As TV screen sizes increase and the resolution grows, audiences will come to expect even more from the sound.

While the use of surround and 3D audio requires greater production and post production effort, the technology offers comprehensive compatibility with modern cinema and DVD, Blu-ray, and DVD media, where 5.1 has been the standard for many years. 3D audio is becoming an increasingly popular format.

One question arises: how are these audio formats reproduced in the living room or on portable devices (smartphone, tablet PC) without excessive effort?  – to position 12 speakers in the room is neither possible nor desirable in most cases. One solution is to use intelligent soundbars such as Yamaha YSP-5600 or speakers that fire sound onto the ceiling and surrounding walls, to create a virtual set of speakers in a room. These techniques can be used to create surround and 3D audio playback, and thanks to the huge takeup of sound bars, offers audiences the chance to experience next generation sound on devices that they already own.

The transition to surround sound and 3D audio is not the only audio-technical challenge when working with HD and UHD. Although HD-SDI interfaces such SMPTE 292M, SMPTE 372M (Dual Link) and SMPTE 425M (3G) and 6G and 12G UHD-SDI offer the transmission of up to 16 audio channels into four groups – as opposed to "normal" SDI with correct phasing - but about the Dolby metadata? While SMPTE 2020-1 (with the variants -2 and -3) defines a possibility, the hardware and associated infrastructure is quite not there yet.

The use of Dolby's metadata (and increasingly many other audio metadata) ensures that devices can decode the sound correctly, however some DVDs and Blu-ray discs and some TV shows are delivered with incorrect audio metadata. This leads to problems with Dynamic Range Control (DRC) and downmixing from 5.1 to stereo - and this affects the audiences’ enjoyment of the programme. 

Likewise, the fact that 95% of all TV sets automatically select the Dolby sound when there are multiple audio streams and, if necessary, down-mix stereo. If the down-mix metadata is incorrect, it will inevitably lead to errors, usually impacting the reproduction of speech quality.

Since 2012 private and public TV stations across Europe have been setting the loudness parameters according to EBU R128. Criticism of annoying loudness fluctuations and disruptive audio tracks overburdening sound processors, are now a thing of the past.

In practice, however, the implementation of the new recommendations is not always trouble free and many broadcasters and producers stumble across different limits for loudness and peak values.

Here, a speedy harmonisation of all broadcasters on uniform targets is desirable. In addition, the achievement of program loudness of -23 LUFS (0 LU) is by no means guaranteed to have created a homogenous, audible mix with good speech intelligibility.

The sound needs to do justice to the technical and artistic capabilities of high-resolution picture transmission of HDTV considering loudness, mono, stereo, 5.1 surround or 3D positional audio, with or without audio description:

This includes, in all cases, compliance to the relevant standards and quality criteria, as described in the delivery requirements of the respective television providers.

Author: Karl M. Slavik, Arte Cast Vienna

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