AC-3 stands for Audio Codec -3.
The market name for AC-3 is Dolby Digital as it is a creation of Dolby Laboratories. The standard is laid down by the Advanced Television Systems Committee (ATSC) in ATSC Doc. A/52A. It was released in 1991.
It comes with the .ac3 file extension.
As a lossy codec AC-3 reduces audio file size without any quality loss noticeable to the human ear.
When audio reaches the human ear, it ignores a certain amount of noise that comes with it. AC-3 removes the audio data related to this noise. As such, the file size is reduced without the audio sounding inferior.
The method use to compress a large audio file into a smaller size is called perceptual digital audio coding.
Previous Audio Coding (AC) Versions
Prior to developing the AC-3 audio format, Dolby had developed AC-1 and AC-2.
AC-3 is however is the first audio coding system that supports multichannel digital audio.
5.1 Channel Format
AC-3 is a 5.1 audio channel format. It supports 5 channels of full bandwidths.
A channel each is available for :
- Front left
- Front right,
- Surround left
- Surround right.
An extra channel is also included for playing sound effects and audio from action sequences in movies.
This is called the Low-Frequency Effect Channel (LFE). It takes up only a small amount of bandwidth compared to any other channel.
More often than not, it is referred to as the subwoofer channel.
Where is AC-3 Used?
The AC-3 audio format is commonly used for the following :
- Theater Movie Screenings (first movie that used Dolby Digital was Batman Returns in 1992)
- Digital Television (DTV)
- LaserDisc (first movie on LD that used Dolby Digital was Clear and Present Danger in 1995)
- Digital Versatile Disc (DVD)
- Game Consoles
- High-Definition Television (HDTV)
- Digital cable and satellite broadcasts
AC-3 has a downmixing function which allows it to be used in systems that don’t support 5.1 audio.
AC-3 vs EAC-3
Dolby has upgraded AC-3 to EAC-3 (Enhanced Audio Codec – 3). The market name for EAC-3 is Dolby Digital Plus.
Sometimes it is also called DD+, E-AC-3, or EC-3.
So, what’s the difference between AC-3 and EAC?
As mentioned earlier, AC-3 supports 1.0 (mono audio) to 5.1 channels.
EAC-3 supports 1.0 (mono) to 7.1 channels and can go up to 15 full-bandwidth channels. In other words, it can support 15.1 channels including a Low-Frequency Effects channel.
The AC-3 audio format supports a minimum of 32 kbits/s to a maximum bitrate of 640 kbit/s.
EAC-3 can manage up to 6.144 Mbit/s.
The sample rates supported by AC-3 are 32, 44.1, and 48kHz.
EAC-3 also supports the above sample rates.
Devices with EAC-3 decoders support the decoding of AC-3.
AC-3 decoders won’t support EAC-3 bitstreams.
How to Play AC-3 Files : Free Media Players
If your existing media player doesn’t support AC-3 audio format playback, you may want to check out the following free AC-3-Dolby Digital players: