– the demos!
Between last issue and this, we’ve heard two demonstrations of Dolby Atmos, the latest and apparently the greatest in multichannel surround sound (see also p79 and p92). The second was in a proper home cinema demonstration room with acoustic treatment and fixed in-ceiling speakers, whereas the first was a touring show set up in a hotel function room, with ceiling speakers hung from an impressive construction of ladders and beams hired from the local Bunnings.
This is not to denigrate the first demo — indeed we were hard pressed to pick a preference between the audible results (they used the same Dolby demo Blu-ray, so comparison was meaningful), which speaks well for both demos, and for this new height-enhanced format in general.
For the record, the first demonstration was from QualiFi, using Jamo speakers and a Marantz SR7009 expanded with an MM7025 stereo power amp for the additional height speakers. The second was from Amber Technology at their Warriewood HQ, using NHT front speakers, 6.5inch two-way in-ceiling speakers (most probably Sonance) and an Onkyo receiver.
We detailed the Atmos concept in a feature last issue. In brief Dolby Atmos adds either two or four ceiling speakers to an existing or new multichannel audio system. If you currently have 5.1-channel surround, you could add two ceiling speakers to have a 5.1.2 Dolby Atmos system, or four to make 5.1.4. You needn’t stop there — home systems can have up to 24 speakers on the floor and 10 overhead (see Dolby’s diagram, right).
This ability to scale is at the heart of Dolby Atmos, because Atmos is not about adding channels, it is about creating a near-sphere of sound using however many speakers you have. And here’s the thing, remarkable as this proposition sounds — the final audio mixdown happens in the AV processor, in the Atmos decoder, not in the studio where the soundtrack was fashioned. There are still audio channels — nine of them, now being called ‘beds’. But the sound engineers can then add audio objects, their sound separately encoded along with metadata that describe their position in three-dimensional space, their physical spread, and the sound’s intensity. Only at the decoder will these audio objects be placed into specific channels, this depending on however many speakers are available, and how they’re set up. So exactly the same soundtrack used in the cinema can be used at home, with Dolby Atmos able to scale down to home layouts — indeed, we gather, all the way to mono if required.
This shows the remarkable computing power that lies within today’s AV processors and receivers, for one thing, but it is most remarkable in delivering an entirely new way of storing and transmitting audio, as separate fragments tagged with metadata to be downmixed at the end user. With 128 audio objects available, the soundtrack guys can have a fair bit of stuff whizzing around the auditorium — or so you’d think. But there is a significant limitation on this, which we thought was audibly evident in both the Atmos demonstrations we heard.
Does it scale? Just a bit — here’s Dolby’s diagram for a system with 34.1 speakers Atmos certainly adds an additional dimension in providing height channels, and of course the demo material comes steeped in ceiling sound to show off the new abilities; you get bombarded with sounds flying above and around you. But what it doesn’t do is come at you, like an axe in a 3D horror movie. The most surprising thing about the Atmos demos was that while stuff was whizzing around everywhere from front to ceiling to rear, there was nothing in the room. Everything is around the room. The second demo delivered some fairly localised positioning behind us, but never did anything go right in front of our face, buzzing like a fly before our nose.
Why? Because in a cinema, if you mixed a fly to be an audio object in front of your nose, then it would appear to be in front of the noses of those in the dead centre rows, but progressively out of position for everyone else in the cinema. Ditto for front to back movement. In the cinema that’s an unfixable problem which can only be addressed by not allowing it — no flies in front of your nose. So Atmos seems to deliver a sphere. The sound moves around, but it does not enter far inside.
Home cinemas have far fewer seats — even just one sweet-spot seat, if you like. So Atmos could potentially deliver a far more localised sonic experience at home than in the cinema. But it won’t, precisely because the exact Atmos soundtrack from the cinema is being scaled down to the home without engineers remixing it for a different environment.
Atmos creates a truncated sphere of sound
It’s all around you
It’s not below you
And the sound is not quite a sphere but a truncated sphere. We were conscious that the sphere was cut off at seat level, effectively the tweeter level of the front speakers. There’s not much to be done about that, and it’s not new — there’s never been any sound down there. But gaining the sound above seemed to create a contrast with the lack of sound