Apple Logic Pro 9 - Manual (Page 788)

Using the Binaural Post-Processing Plug-in
The Binaural Post-Processing plug-in is available in aux and output channel strips. This
plug-in allows you to apply various compensation modes on a stereo bus or
output—through which several, or all, binaural signals are routed. This saves CPU power
and makes it easy to switch between compensation modes.
For details about this plug-in, see the Logic Pro Effects manual.
Binaural Hearing—Binaural Recording—Binaural Panning
An important part of mixing audio signals is the placement of individual sound sources
at different spatial positions. Most common recording and mixing techniques simply send
a given signal at different levels to the available loudspeakers—two for stereo, or more
for quadraphonic or surround setups—to create a virtual sound stage.
This approach is somewhat flawed, however, as human beings are able to locate sound
sources at different positions with just two ears. Virtually all spatial information for all
sounds is included in the two signals arriving at the two eardrums. From these signals,
human beings can determine characteristics such as inter-aural time and level differences
and—based on the listening experience—information about the spatial origin of the
sounds being heard. Are they coming from in front or behind, from the left or right, or
above or below? This ability to perceive where a sound originates from is referred to as
binaural hearing.
In theory, the spatial positioning of any sonic experience can be reproduced during
playback, so no special techniques need to be employed during recording. There is,
however, one drawback to this approach: every person has differently shaped ears and
different body and head proportions, all of which influence the way sound signals arrive
at the eardrum—not to mention aspects such as hearing loss, subjective responses to
the sounds being heard, and so on. Given these physical differences, each person listening
to the same sound source, while standing or sitting in the same position, will hear slightly
different binaural signals.
Therefore, perfect reproduction would only be possible if you could make a recording
with tiny microphones placed inside your auditory canals. Because this is impractical,
binaural hearing has been emulated in sound laboratories by using mannequin heads
with built-in microphones. This approach has led to binaural recordings to fit the average
person, which are more or less compatible with the way most people hear.
Playback of binaural recordings is best suited to headphones, ideally combined with
signal conditioning (processing) that ensures the signals are accurately reproduced. Given
a specialized listening environment, it is also possible to reproduce these signals with
loudspeakers, utilizing a process known as crosstalk cancellation.
788 Chapter 27 Mixing