Binaural Audio

Drawbacks to typical stereo recording practices:

Standard microphone recording formats do not include the binaural cues that we have documented in the previous section. The interaural time differences (ITD) will not be present unless the microphones are placed at a similar distance that the ears are apart. The interaural amplitude differences (IAD) for high frequencies will also be absent since microphones are smaller than the size of the head, and any lack of diffraction around the microphone will be at even higher frequencies. And, of course, pinna colouration will be completely absent. Finally, any effects from the head and torso will also be missing.

One of the reasons that binaural audio is not more popular is because binaural recordings only sound good on headphones, while speaker mixed recordings sound fine on headphones.

It is now possible to create 3D directional sound cues and to synthesise the acoustics of virtual environments quite accurately using digital signal processors (DSP), and it is this area of virtual environment simulation for computer applications that is receiving the most commercial attention for binaural technology today. Flight simulators, computer games, virtual reality applications and architectural auralisation are all areas that are benefiting from these develop- ments. It is also possible to use such technology to synthesise ‘loudspeakers’ where none exist, using binaural cues, as employed in virtual home theatre systems (see below).

3D Rain

Problems with binaural systems

People’s HRTFs are different (to varying degrees), although there are some common features, making it difficult to generalize about the HRTFs that should be used for commercial systems that have to serve lots of people.
Head movements that help to resolve directional confusion in natural listening are difficult to incorporate in reproduction situations.

Visual cues are often missing during binaural reproduction and these normally have a strong effect on perception.
Headphones differ in their equalization and method of mounting, leading to distortions in the perceived HRTFs on reproduction.
Distortions such as phase and frequency response errors in the signal chain can affect the subtle cues required.

Oscar

Neuman Head

Above the head

Left to right trajectory around an artificial head, then front centre to above the head. Source: Cook 26

Duda recordings

Moving from a reverberant room to an anechoic chamber
Binaural cues in the frontal plane (left, above, right, below)

Music in 3 examples: Left track mono; Right track mono; binaural Check out the clarinet over your right shoulder!
Passing jet in 3 examples: Normal stereo; Low-bandwidth binaural; High-bandwidth binaural; Which gives the best impression of the jet being overhead? Source: Duda

With HRTF

The original chainsaw, heard first, was recorded in a stationary position, then using HRTF processing it appears to fly around you (try not to duck!) (Source: Pierce 39 & 40)
The footsteps are recorded moving in place, and then processed as if they were first in a dry, then a reverberant stairwell. Do the steps go up or down? Does your contextual knowledge of stairwells help the vertical localization?

Fireworks display in Vancouver. Source: WSP VFile 2, take 11
The Virtual Haircut