04.04.2008 Virtual Barber Shop

One of my students forwarded me this mp3 the other day.

The noble Internets have so far been unable to tell me who made it. It's on YouTube and Metacafe, but see, when you upload to those sites, they super-compress the file, and since it was compressed (mp3) to begin with... well, it kind of messes with the binaural-filter effects of the recording. So! If this is yours, sorry to post it here without your permission. I'd love to give you credit or link to your actual site. Please say hi. Otherwise, for everybody else... this is a cool sound experience.

The thing you need to know is: Binaural listening requires headphones. If you just put this on through your speakers you'll be left with nothing but some cheesy voices, and wonder what all the fuss was about. The total 100% separation you get between the two channels is what makes the experience immersive, what makes someone able to walk "behind" you or have a sound move "over" your head, instead of just pan left-to-right.

Also, none of the other blogs Google told me about go much into what this type of recording is, or how or why it works. The (relatively) short explanation is that there are two reasons we hear sound as coming from a certain location:

  1. The sound hits your ears at two different times, and/or
  2. The sound hits your ears at two different volume levels.

    These two will give you simple left-right information.

  3. The sound has been filtered by your ears, and
  4. The sound has been partially blocked by your head.

    This is what gives you front-back information. I really had to think about this the first time someone brought it up, but if your ears were just hearing-points, you wouldn't be able to tell the difference between straight-ahead and directly-behind. But our funny-shaped ears absorb and block out specific frequencies from sound, so if those frequencies are lowered when the signal hits our brain, the brain says "behind".

  5. Last, sounds that happen very close appear to be more bass-heavy, in what's called the "proximity effect"... this is why the clippers (and even the scissors!) really roar when they're right by your ear, and also why radio announcers have those insanely grounded, gravitas-laden voices-- they're just right up on the mic.

So, in recording you can either (1) set up a somewhat realistic dummy-head with mics in the ears, so the sound gets the same treatment it would with a person's head, or else (2) record the sound normally, and then process it somehow to simulate ear-absorbtion and whatnot. Most of the time it seems like you either want this kind of recording, or you don't, and so the dummy-head thing is most common. However, some other folks are working on the algorhythm approach-- for example, for binaural post-processing to give craaazy headphones-only mixes for music like Cornelius did on "Point".

Posted by charlie at April 4, 2008 01:01 PM

Comments

This is so cool! There's a whole ton of research in the audiology community right now figuring out how recordings like this could be used to create more accurate hearing aids. Plus we have one of those dummy-heads in our lab. It's kind of freaky. In a related thought process, it's cool that they can recreate positioning, which is largely determined by the pinna - the outer ear, the part that sticks out from your head. Here's an additional cool experiment(where cool = you're a huge nerd like me) to try: Have a friend shake a pair of keys behind your head where you can't see them. As your friend moves the keys from left to right or up and down, you can tell generally where they are in relation to you. Now cup your hands behind your ears, and repeat.

Posted by: Kay at 04.04.2008

That's awesome! We learned a bit about this in my Perception class last year - fascinating stuff! The professor played a sample of a recording like this over the speaker system in the lecture hall and scared the crap out of some of my classmates in the back.

Posted by: Laura at 04.05.2008

They say in the recording who made it... the last 20 seconds or so are an ad for special hearing aids that return the spacial awareness to people using aids. He whispers "Cetera" right in your ear... and tell you thats the product... I just googled that and the name of the company is Starkey (thus "Starkey's Virtual Barbershop) whispershttp://www.nal.gov.au/Import%20web%20articles/Import%20NAL%20Conf/abstracts/agnew.htm

Posted by: Evan at 05.18.2008