Dolby Atmos on Playstation 5

I wrote about Dolby Atmos before. And with a recent Playstation update, there are things to dicuss.

Atmos? Remind me

About a year ago, I wrote a post about speaker setups and audio formats.

A recap. Stereo, 5.1 and 7.1 speaker setups all result in a 2D sound. That’s cool, and much better than 1D (mono) sound, but the real world is 3 dimensional. When you walk out on the street, you can hear airplanes above you. Height speakers add to the mix to provide true 3-dimensional sound. This results in 5.1.2, 9.2.4, etc speaker setups, with the third number signifying the height speakers.

However, the speakers are only one side of the equation. On the other side is the audio signal producer. A computer, Blu-ray, or something like a Playstation 5 has to produce those 3d sounds. These devices produce a stream of audio data that is sent to the speakers. If that audio data is 2-channels of stereo, your fancy 5.1.2 home theater set won’t utilize the rear or height speakers very well. So the device matters. Although, note that if you play a Blu-Ray, then it’s not the Blu-Ray player producing the audio, the audio track is streamed directly from the Blu-Ray disc. In that case, it’s the disc that needs to contain the 3d audio data.

Dolby Atmos is an audio format that allows a device or disc to encode audio with both rear speakers and height speakers. And more, in fact, but I’ll get to that. A competing format is Sony’s 3D Reality Audio format, which they crooned about at the Playstation 5 introduction. Unfortunately, support for 3D Reality Audio hasn’t really taken the market by storm. I’m not audio expert, but I haven’t really found any support for it outside of Sony products.

The Encoding

For movies, the above problems are relatively simple. The Audio data is produced along with the movie over a period of months. When they create a Blu-Ray, the data is encoded on the disc and your player can send that data directly to the receiver (even a Playstation 5).

So, let’s zoom in a bit on video games. Because that is much harder. A video game produces a dynamic game world. Take Horizon: Forbidden West for example. Players move through a vast game world, with dinosaur robots in front, behind, and above them. For visuals, the Playstation renders the 3D world to your television real-time.

And for audio? The process is similar. The game engine produces a (large) number of audio sources: one is your character, which produces sounds like footsteps and voice lines. Then there are the dinosaurs producing squawking and moving sounds. And sounds from the environment. Maybe some NPCs are talking in the background. All of these sound sources have a 3D position.

Next, the game engine or underlying software/hardware transforms those audio samples to the proper audio encoded format. In mono that would mean mixing them all together at different volumes depending on position. In stereo, sounds are added to a left and right track, with one louder than the other depending on the 2D position. For 7.1.4, there are 12 tracks. For each of these, the correct volume based on the 3D position is calculated, so sound from above sounds louder in the height track, for example.

3D complications and lag

So, you’d think we’d be done. Channels calculated, the device can send them to the speakers and we have sound. And that is the brute force way to do lossless audio. PCM is a format to send the audio data directly to the speakers.

Yet, there are other formats. Like Atmos. Many formats use compression to be able to cram more data into less bits. For a console to output Atmos, it needs to take the channel data, apply the appropriate compression, then send out the result.

And it gets even more complicated. You see, Dolby Atmos is not just a number of speaker channels. The basic ‘bed’ of the Atmos format is a 7.1.4 stream, so a center speaker, and three speakers to the left and right (one at the front, one in the middle and one in the back), a subwoofer, and four height speakers (front and back, left and right).

On top of this bed, a Dolby Atmos can contain up to 118 dynamic channels that have a position. The idea is that a sound designer can — for example — play sounds on the 7.1.4 bed, then add a helicopter sound that moves around the room in 3D. This is mostly useful for setups with more than the 10 speakers described, like in an actual theater.

All those calculations add up. The XBox Series X, which has had Dolby Atmos since its release, struggles with lag when outputting to Dolby Atmos.

Playstation and Atmos

So, how does Playstation 5 do? The device has an advantage over the XBox, in the form of their hyped Tempest Audio chip. This specialized audio chip normally produces Sony 3D reality audio, but with the new update, it now produces Dolby Atmos. According to Sony, they’ve managed to use the tempest engine to do the calculations and produce a 7.1.4 Dolby Atmos signal directly from the Playstation 5. And because of the dedicated chip, it should be lag free.

Wait… A 7.1.4 signal? As I just wrote, Atmos supports another 118 dynamic channels. By the sound of it, Sony opted not to use those. Which is logical, because Reality audio uses only 3d sound sources. The tempest chip receives a large set of sound sources and has no way to know which should be in the ‘bed’ and which should stay dynamic. So Sony opted to mix everything into the 7.1.4 signal. Of course, you won’t even notice this ‘problem’ until you add more than 7.1.4 speakers. So, unless you have a real-life theater hooked up to your playstation, you won’t even be able to notice.

In short: I’m happy!

I can now play Horizon Forbidden West or the upcoming Final Fantasy 7 Rebirth with actual Dolby Atmos sound. I tested Horizon earlier and was very pleased to see the Atmos logo pop up on my receiver. It’s a shame we had to wait over two-and-a-half years for it, but it’s great that it’s here now.