Binaural Audio

Not long ago…

I attended an audio symposium and was able hear a presentation by Edgar Choueiri on 3D audio and it totally, completely, blew my mind. I’m not going to go into extreme detail here, but the essence of his lecture was around achieving independent VR sound fields without the use of headphones or massive arrays of physical speakers. Basically a personal VR 3D audio mix beamed right to your ears that is totally independent of someone else’s mix who might be sitting right next to you. Crazy stuff. Awesome stuff.  

 

Of course I had to try to DIY this myself with whatever tools I had in my studio. To achieve this at the highest degree you basically need 4 things – a personal Head Related Transfer Function (basically mapping the shape of your ears to determine how they EQ sound coming into your head), individualized binaural rendering from high-order ambisonics audio (dynamically using the HRTF to render the audio as a “personalized”  binaural recording before output), individualized and spatially uncolored crosstalk cancellation (mimicking appropriate spatial delay between your two ears), and advanced head-tracking (making sure the speakers are projecting the sound directly at your ears as your head moves.

Oh yeah, simple.

So I knew mapping my ears and using it to virtually render a personalized binaural recording was a bit beyond my initial scope here, so I set off on my test with the goal of producing a generic binaural recording with physical-microphone techniques (props!) and then using another physical barrier to provide the crosstalk cancellation between two speakers, which I would (unfortunately) have to sit directly in front of and not move my head (no fancy head tracking in my li’l studio) at all as I listened to the recording. How would this all work out? Could I create some amazingly immersive 3D audio without headphones?

I immediately began researching binaural microphones only to find (no big surprise) they’re rather expensive. There’s a budget model from 3Dio that looks pretty slick, but since (at the moment) I’m just having fun doing some test projects I felt it was still a bit too much of an investment for now.

So I decided to make my own! I have a pair of Samson C02 condenser mics which seemed like a perfect choice. The cardioid pattern of the C02 is one that is optimal for eliminating ambient sound and capturing audio directly in front of the diaphragm. Perfect!

Next I needed some ears to create an HRTF for each mic.  I found some cheap “prop” ears at a costume store that looked right on point. By cutting out a slightly larger ear canal I was able to snugly fit each ear over a C02 and boom, I had my binaural microphone.

The last thing I did – before running the C02’s as a stereo input into my trusty ole’ Babyface – is add some cardboard isolation sheets behind each ear, to again hopefully maximize the realism of my human-head reproduction.

 

For my recording I tackled something incredibly simple and basic – my sofa. Well, me sitting on my sofa as normal things around my house went on; opening the sliding glass door, hanging my Ohio State flag (go Buckeyes!), turning on the TV, opening the blinds behind me, etc.  

The recording itself went off without a hitch, but my first test of the recording is where I ran into some issues. Before I constructed a physical barrier to use with my studio monitors I did some initial listening/testing with my sweet, sweet Beyerdynamic headphones. Unfortunately the sense of immersion just wasn’t captured – I ended up with a pretty spatially smerged stereo recording.

In considering where my experiment went awry, I have to think it was my homemade binaural microphone. The “ear canal” – or really just the size of the microphone’s diaphragm –  is large enough that I think it captured too much audio directly before it could be EQ’d into a proper HRTF by my fake ears. Since the true 3D effect was missing with a good set of headphones, I didn’t move forward on setting up a pair of speakers with physical boundary to provide the crosstalk cancellation. I basically considered this first attempt complete. But it was a fun experiment all the same, and the first of many more within the world of 3D Audio. And hey, my cats ended up with awesome new creepy cat toys (the ears!), so there’s that.