Australian T3 - - DOLBY ATMOS -

So it seems that Dolby Atmos is only the be­gin­ning. Dolby has a new next-gen au­dio for­mat wait­ing in the wings, which evolves the con­cept of ob­ject-based au­dio for broad­cast­ers. AC-4 builds on the core idea be­hind Atmos, but of­fers an even more ver­sa­tile toolset.

With AC-4, broad­cast­ers can flag spe­cific ob­jects dur­ing the en­cod­ing phase, which an AC-4 de­coder in a TV will un­der­stand. For ex­am­ple, di­a­logue, often crit­i­cised for be­ing in­dis­tinct, can be raised with­out af­fect­ing any other el­e­ment in the sound­field. Spe­cific ef­fects, such as bird­song or gun­shots, can be tagged. While AC-4 can han­dle 126 ob­jects, that num­ber would never be trans­mit­ted at the same time. Most TV broad­casts are ex­pected to con­sist of around 12 ob­jects at a time, plus a con­ven­tional 5.1 sound mix.

With AC-4, view­ers can fine-tune their lis­ten­ing ex­pe­ri­ence. Imag­ine watch­ing a sport­ing event where you can choose be­tween mul­ti­ple com­men­taries, or sim­ply re­move the com­men­tary al­to­gether. Cru­cially, AC-4 com­pres­sion is twice as ef­fi­cient as Dolby Dig­i­tal Plus. Where tra­di­tional 5.1 re­quires be­tween 384kbps to 448kbps, Dolby Dig­i­tal Plus utilises 192kbps to 224kbps. How­ever, AC-4 de­liv­ers the same qual­ity for 5.1 at about 96kbps.

So when will you see (or rather hear) AC-4? Dolby sug­gests the first com­mer­cial ser­vices could kick in as early as 2019 on all ma­jor TV man­u­fac­tur­ers.

We had an early pre­view of Dolby AC-4 with some en­coded foot­ball footage. Un­like a con­ven­tional broad­cast, we could select from mul­ti­ple lan­guages, as well as Home and Away com­men­taries. Switch­ing be­tween those is in­stant. With­out a next-gen au­dio codec like AC-4, this kind of au­dio in­ter­ac­tion would not be pos­si­ble over broad­cast.

Soon we could be en­joy­ing live Dolby Atmos au­dio, with an un­prece­dented level of per­son­al­i­sa­tion. You ain’t heard noth­ing yet.

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