Monaural sound is a single channel or track of sound created by one speaker and is also known as Monophonic sound or High-Fidelity sound. Monaural sound was replaced by Stereo or Stereophonic sound in the 1950s.
Stereo or Stereophonic sound is two separate audio channels or tracks of sound reproduced by two speakers. Stereo sound provides a sense of directionality because different sounds can be heard from two directions. Stereo sound is the most common form of sound reproduction.
Surround Sound or Multichannel Sound:
Surround Sound, also know as Multichannel sound, is created by at least four and up to seven independent audio channels and speakers placed in front of and behind the listener. The purpose is to 'surround' the listener in sound. Surround sound can be recorded on DVD music discs, DVD movies, some VHS tapes and some CDs. Surround sound became popular in the 1970s with the introduction of Quadraphonic sound, also known as Quad. Since that time surround sound or multichannel sound has evolved and is widely used in home theater systems. Multichannel sound is also known as 5.1, 6.1 or 7.1 channel sound.
5.1 Channel Sound:
5.1 channel sound is an industry standard sound format for movies and music with five main channels of sound and a sixth subwoofer channel (called the point-one channel) used for special movie effects and bass for music. A 5.1 channel system consists of a stereo pair of speakers, a center channel speaker placed between the stereo speakers and two surround sound speakers located behind the listener. 5.1 channel sound is found on DVD movie and music discs and some CDs. The two most common 5.1 channel formats are Dolby Digital 5.1 and DTS Digital Surround.
6.1 Channel Sound:
6.1 channel sound is a sound enhancement to 5.1 channel sound with an additional center surround sound speaker located between the two surround sound speakers directly behind the listener. 6.1 channel sound produces a more enveloping surround sound experience.
7.1 Channel Sound:
7.1 channel sound is a further sound enhancement to 5.1 channel sound with two additional side-surround speakers located to the sides of the listener’s seating position. 7.1 channel sound is used for greater sound envelopment and more accurate positioning of sounds.