This is the first part of a two part series on multichannel audio. The first part will focus on the hardware and physical attributes and requirements for multichannel audio, followed by an article about all the software formats available.
A little bit about how we hear
Most of us have noticed that we only have two ears. The part that we see helps to funnel sound waves to our tympanic membrane, which is just like the membrane on a microphone. Vibrations of the tympanic membrane transmit vibrations to various signal amplifying bones and finally to the cochlea where the mechanical vibrations are integrated into electrical signals, just like a coil in a microphone. Interestingly the cochlea is organized by frequency - certain parts of it respond to certain frequencies. Thatís how one ear hears, but the sonic environment we experience is a combination of the sounds from both ears. Given that the ears have a finite space between them, the sound reaching one ear is delayed compared to the other. This delay between the sounds reaching our ears gives us the stereo effect and helps us to localize sounds in our environment.
Ok, so two ears can give us 360 degree localization of sound, but why do we need more than two speakers? Actually if you had very good headphones, you could probably recreate a 360 degree environment, although your recording must be designed for headphone listening. Another issue to consider is the ideal listening spot. Often we do not listen to music or enjoy movies by ourselves, so it would be nice if more than one person could experience the surround sound. With more speakers, you can create more ideal listening spots.
Our first experience with multichannel audio was probably at the movie theaters where we were in awe of all the speakers around us. I remember going into the theater and counting how many speakers there were around us. Home usage of multichannel audio has been around for a while. Back in the 1970s there were many quadraphonic recordings on either LP or 8-track that offered four listening channels. The effort was aimed at surrounding the listener with sound to more closely create the ideal listening environment.