How do you think a Human ear can tell if a sound is coming from their left or their right?
Our brain does a lot of processing behind the scenes crushing all this information to give us the perception of sound in a given space. The main way this happens is via something called ILD and ITD. ILD = Inter-aural Level Difference ITD = Intramural Time Difference.
Our ears can locate a specific sound in space give these two primary factors, when one sound reaches the left ear louder and softer in the right ear, then we will perceive the sound to be coming from our left. Similarly, if the sound reaches the left ear first, which it will if it’s closer to the left ear and reaches the right ear a little later then our brain will perceive the sound to be coming from the left.
All of this makes sense, but then how can our brains perceive if a sound is placed front or back?
Well, our brain is running a bunch of other complex algorithms other than this that will help us place the sound front in back, and that also has to do with the shape of our ear. If you closely observe, a sound coming from front vs the same sound coming from behind will have very different tonalities. This is because when a sound is played or created behind us, the shape of our ears cuts out some of the higher frequencies which we co-relate to a sound being created behind us.
Now that we understand the basics of this concept, it can be much easier to understand how Spatial Audio works.
Up until now, most of our commercial music has been mixed in “Stereo”, i.e two-channel format. When we put on headphones, we get a sense of sounds being placed in a field around us from Left to Right. Spatial Audio takes this to the next level, but not giving you the freedom to place sounds left and right but also place them, behind you, above you, essentially in a 360 degree sound field.
But how does this work?
Apple in collaboration with Dolby has come up with an encoder, that takes the sounds placed in a “Dolby Atmos” Setup i.e 7.1.2, and encodes them in a way that you can perceive the placement of those sounds on you’re headphone.
Imagine you pan a sound on your mix in Pro Tools, what this encoder will do is, run this through a complex set of EQ/Reverb and time filters to trick your brain into thinking that the sound is placed behind you.
Does this mean that now we have 7.1.2 channels to work within stereo? Of course not, all this means is that now we can pan these sounds and emulate them in a way that they sound like a 7.1.2 within a stereo. These emulations also have their own set of limitations, of course, not all sounds panned beyond the stereo field sound accurately. They are at best a close imitation of the real thing.
This is not just limited to music, soon we will have Netflix and Prime Video Films that will be Spatial Audio compatible which will give you a close proximate, “Surround” or 360 degrees feeling of the mix. Since most of the mixes nowadays are done in Atmos, it isn’t that difficult to downmix them into a Stereo format, which can then be played over a pair of headphones.
Currently Spatial Audio is available only on a few Apple compatible devices
You can find the details of the devices in an article by Apple here
Spatial Audio is also available on Mac devices which have the MacOs Big Sur 11.6
Yes and no, there are some devices which according to Apple are Spatial Audio Compatible but we find that accurately creating a sense of 3D space using speakers is near impossible. In all our experiments, the Spatial Audio mixes played over speakers lack distinct character. So if you want to get the best experience out of this, you would be better off sticking to listening to a mix over your headphones.
Spatial Audio brings something new to the current way that we listen to and consume audio, but it still has a long way to go in terms of adoption from listeners. Engineers and Mixers are still finding new ways to make the best of this new platform and the next year will be very interesting to see how this technology pans out, this could very well be the next jump In audio like Apple claims it to be.