From the preliminary, people had known to use the raw materials such as: wood, stone, leather ... to create melody and rhythm sounds serving for their emotional life.

Along with economic, social, cultural and human development, the field of audio technology does not stop developing in order to catch up with more and stricter demand and requirements of people, especially music and film. The following is a summary of steps that developed in the spirit of short and easy to understand.

•  Mono:
Audio signal is recorded on a track (channel) while playing. At playback, the input player reads only and restores its primitive signal by following:

This is the simplest audio format and providing bad audio quality about music and watching movie.

• Stereo:
Primitive signal is processed original style and recorded on 2 separate channels (track), called the left channel (L) and right channel (R), on archive tape or material. When playback, the output player will read on 2 channels and restore the primitive signal by the following:

With Stereo audio, the signal between left and right channel to the late phase, creating big sound effect. It makes listeners do have feelings the sound is more lively from two channels. In this time, you can enjoy music with Stereo audio in a relatively complete, even trying to please strict listeners.

• You often heard about the Sound 2.1 in the market. It is an audio Stereo adding a subwoofer loudspeaker, called a point one. This baritone is separated from the left and right channel and has been brought to subwoofer loudspeaker in order to enhance separation sound become stronger, clearer, and more precise for listeners feel better about the beauty of sound.

• Quadraphonic (audio 4 channels):
In the 70s, some television channels had tried to play audio 4 channels (Quadraphonic), that means the sound from 4 points and late phase between the channels, but this technology is not developed.

• In essence, sound 4.1 is the 4-channel sound (Quadraphonic) includes: Front-L, Front-R, Rear-L, and Rear-R. Only subwoofer channel (.1) is separated into 4-channel to baritone speaker.

 • Dolby Digital 5.1:
In the last 80s to 90s, Dolby Company began applying the Dolby Surround technology, and later applying Dolby Pro Logic for Home theater system. 

Dolby Surround Pro Logic II:
For compatibility with Stereo audio devices which existed previously, Dolby Company offers a method of processing audio Pro Logic II. That is to create Surround 5.1 on the basis of two-channel Stereo, creating circle audio space effect in watching movie and enjoying music, etc.

To enjoy Pro Logic II system, it is required that your system has to meet the following requirements:
• Stereo signal source
• Coding system Pro Logic II on DVD player or Ampli
• Speakers 5.1

Down mixing (DownMix):
Changing system 5.1 into Stereo
Digital audio coding (AC-3)

When transfer from the normal record technology to the digital record, audio after being digitized with too big capacity will affect on the ability of archive. A CD is only 70 minutes for enjoy music.

Therefore, Dolby Company developed new digital audio coding referred as AC-3, with this technology allows the digital audio with lower frequency, but still achieves the sound quality desired. Thus, storage audio file AC-3 is reduced significantly, saving a capacity storage space. With this technology, Dolby Digital gives you the 6 audio channels which are really attractive and lively in order to enrich the life of enjoying music, watching movie and playing game at your own home. The 6 audio channels in particular are:

• 2 Front-L and Front-L channel
• 2 Rear-L and Rear- R channel
• 1 center channel
• 1 subwoofer channel

Therefore, it is called as Dolby Digital 5.1
• To enjoy system 5.5 (AC-3), it is required that your system has to meet the following requirements:
• DVD…according to AC-3 format
• Coding system AC-3 on CD player or Ampli
• System 5.1