Meeting Topic: Dolby Atmos — Immersive Audio: From the Cinema to the Home
Moderator Name: Graeme Huon
Speaker Name: Nick Engel, Dolby's Senior Director of Consumer Entertainment
Meeting Location: SAE Institute, South Melbourne
Nick started with an overview of the history of Dolby's last thirty years of cinema audio, encompassing Dolby Surround, Digital Surround Ex (5.1), and Dolby Surround 7.1. He then moved on from these channel-based systems to the object-based spatial audio description of Atmos — describing position, size and diffusion of individual objects.
He then contrasted the benefits of channel-based (established work-flow, tools, and techniques; easy to render and monitor; direct artistic control over key loudspeakers; and efficient storage) and its key liability (spatial resolution limited by channel count) with object-based's major benefit (scability)and its liabilities (lower efficiency for complex soundscapes and steep learning curve for mixers).
He went on to describe speaker layouts for an Atmos theatre, highlighting the additions needed to a surround-equipped theatre.
As well as the overhead speakers, additional surround speakers are needed towards the front of the room (to permit smooth panning from screen to the sides). Additionally, the surround speakers need to be upgraded to full-range devices, and side wall sub-woofers added for bass management. He also mentioned that, with Atmos, the SPL reference level of the rear speakers has been increased from 82dB to 85dB, to match the SPL of the screen speakers.
He went on to describe the industry collaboration process that took place in the creation of the Atmos system.
Nick then discussed how to reach out beyond the cinema, and deliver immersive audio to consumer devices, such as mobile devices, TVs, PCs, gaming consoles and Virtual Reality devices.
He covered the content creation workflows for a home cinema mix, as well as a live content creation workflow for sports and live music events.
He then outlined the challenges of delivering the bitrates involved, and the compression required for practical delivery and playback. Conventional 5.1 requires a compression ratio of 23.4, but Atmos requires a ratio of 390.
He covered the basic principles of both the audio coding and spatial coding used in this compression, ultimately describing the Dolby AC-4 codec and its flexible support for multiple device types.
He then described the AC-4 Immersive Stereo system which takes an Atmos or 5.1 signal and encodes it as a stereo signal (LoRo) which is delivered to a mobile device where it can then be decoded into an Atmos experience for headphones or mobile speakers.
Examples of home playback speaker setups were then described, including a method of avoiding installing overhead speakers by using elevation speakers where floor-mounted speakers bounce the signals off the ceiling. It is a process that he described as working "surprising well".
Nick then covered sound source virtualisation, where Interaural Time Difference, and Interaural Intensity Difference properties are used to localize sounds onto a virtual sound stage that exceeds the properties of the playback environment in terms of speaker numbers and locations and sound stage size. He went on to describe the use of the Head Related Transfer Function (HRTF), and Binaural Room Impulse Response (BRIR) in this virtualisation. He covered both headphone and speaker virtualisation.
The relevant standards from the ITU (BS.2076 BWAV ADM), SMPTE (Interchange, Metadata, Immersive Audio for Cinema), ETSI (TS102, TS103), ATSC 3.0, and DVB (NGA — Next Generation Audio) were then enumerated.
He then spoke on how we could experience Dolby Atmos, covering cinemas, Atmos capable TV sets, and Windows-based devices (PCs, tablets, and gaming consoles) — he noted that Windows 10 has Atmos support built in, as does their Xbox gaming console.
Mixing in Atmos was then covered, mentioning the Atmos capabilities of Soundfirm's Melbourne facilility, and covering the Atmos capabilities now available in ProTools for both production and mastering.
Nick concluded his presentation with an overview of the future of Atmos where he indicated that it was being seen used increasingly in live sport, and live music (live events and clubs).
The evening concluded with a Q&A, where Nick fielded many questions from the audience.
Written By: Peter Smerdon