An Inside Look at Immersive Audio

Immersive audio pioneer Felix Kr ckels talks to TVBEurope about next generation audio, how to prepare, and how to mix the audio for live broadcasts.

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Published: November 26, 2020

Immersive audio pioneer Felix Kr ckels talks to TVBEurope about next generation audio, how to prepare, and how to mix the audio for live broadcasts.

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Felix Kr ckels is a certified audio engineer who has been involved in immersive audio mixing since 2012. He was the audio engineer for the international feed at UEFA Euro 2008 and the 2010 FIFA World Cup, both of which were produced in 5.1. The FIFA World Cup 2018 in Russia was another highlight of his career: it was produced in Dolby Atmos.

Kr ckels became involved in 3D audio almost by accident when he was asked to support an immersive project for the Confed Cup in 2013 as a test for producing the FIFA World Cup Final in Brazil, in 2014, in 3D/immersive audio.

While the production of the 2014 final still required post-processing and mixing (the 3D audio rendition was not available for the live telecast), live production came along at the Women's World Cup in Vancouver the following year. For this occasion, the entire signal path, from the microphones through to end consumers' homes, was successfully covered for the first time. The tournament in Russia, for its part, was telecast in quasi-ATMOS 3D/immersive audio.

One Step Removed According to Kr ckels, the most important mixing challenges are the bonus features afforded by immersive audio: the A1/sound supervisor/audio engineer (different monikers for the same person) has to bear in mind the freedom and flexibility granted to end consumers of the audio content.

This is due to the object-based nature of the MPEG-H or ATMOS audio material: end consumers can individualise the streams they receive by changing the levels of the ambience, the commentator, etc. The A1 therefore needs to take a step back and prepare the material in a way that allows for different mixes.

With next-generation audio (NGA) object-based audio productions, focusing on listening scenarios is no longer possible: sound supervisors create a three-dimensional space based on a given number of objects. This audio content can be consumed using binaural headphones, speakers (2, 4, 6), soundbars, up-fire speakers, etc., and the result can no longer be completely predicted by the A1.

Enter the rendering principle: the audio objects supplied to end consumers contain coordinates rather than channel or speaker references. These allow the decoder at home to render the immersive audio content as a translation/adaptation of the panning information to the real-life speaker setup in end consumers' homes.

Sound supervisors still need to check whether their mix works in a variety of listening scenarios, even though none of them may correspond to the rendition at home. Up to four presentations are prepared and checked against typical final speaker layouts an A1 needs to check at regular intervals (5.1.4 5.1 Stereo, all with and without commentary-for four presentations).

Among the presentations Kr ckels prepares is a creation he's developed with the Dolby team called the Pub Presentation , where the crowd at the sports venue is barely audible, leaving ample room for the cheers and boos produced live by the people watching the game at the bar. Field-of-play audio details, like ball kicks, tackles, whistle and groaning noises, on the other hand, are hyped.

So Far, So Immersive Individualisation of 3D/immersive audio can be a blessing in disguise, though: the added flexibility can easily lead to situations where tweaks by end-users blur the audio content beyond recognition.

This explains why sound supervisors of immersive audio productions often favour a conservative approach, with relatively few bells and whistles. They know that they are unable to control what viewers at home do to the incoming presentations and therefore limit the options at the source.

The production as such is relatively straightforward and very similar to 5.1 scenarios, except for the added dimension (height/elevation), which merely requires additional busses on the mixing console.

Immersive Nuts and Bolts The most important consideration for an A1 is the ease with which they can monitor the various presentations and formats (stereo, surround, 3D) right from their console. Lawo's mc mixers have allowed audio engineers to control all relevant parameters for over a decade, because speed is of the essence.

As the console itself is only one element-with an external renderer contributing other aspects-the ability to control all relevant devices via one user interface becomes paramount. Thanks to their integration with Dolby and their open Ember control protocol, mc consoles are an important step in the right direction.

As far as 3D microphone placement is concerned, the first step is to look for a venue's sweet spot , i.e. the position where you can hear everything. This position is usually located close to camera 1, i.e. the main camera.

The 3D microphone is suspended from the roof, at a suitable distance from the crowd. It serves the same purpose as a suspended microphone used to capture the overall sound of a symphonic orchestra. For reasons of intelligibility and flexibility, spot microphones are positioned close to all important sound sources. The resulting signals are combined to make acoustic sense for the signals coming out of nine speakers.

Kr ckels likes to work with three planes for his mixes: a

LINK:	https://www.tvbeurope.com/audio/an-inside-look-at-immersive-audio...
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