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What is the AC-3 Audio Format? Where is it Used and How to Play it?

AC-3 audio format

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,
  • Center,
  • 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 :

  1. Theater Movie Screenings (first movie that used Dolby Digital was Batman Returns in 1992)
  2. Digital Television (DTV)
  3. LaserDisc (first movie on LD that used Dolby Digital was Clear and Present Danger in 1995)
  4. Digital Versatile Disc (DVD)
  5. Blu-ray
  6. Game Consoles
  7. High-Definition Television (HDTV)
  8. 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?

Channels Supported

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.

Bitrate

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.

Sample Rate

The sample rates supported by AC-3 are 32, 44.1, and 48kHz.

EAC-3 also supports the above sample rates.

Decoder Support

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:

Free Video Workshop