AC-3 (Dolby Digital)
AC-3, also known as Dolby Digital, is an audio codec that carries surround sound, typically 5.1 channels, alongside video. AC-3 was introduced in the early 1990s and became standard on DVDs, Blu-ray discs and broadcast TV. Most home theater systems, soundbars and smart TVs can decode it. Compared with newer codecs, AC-3 needs higher bitrates for the same quality.
Why it matters
AC-3 lets viewers with home theater systems hear surround sound, which premium film and sports audiences expect. It is supported by a huge base of TVs and receivers, but it uses more bandwidth than newer formats, so services weigh reach against delivery cost.
How it works
- The audio is mixed into up to six channels, usually 5.1 (five speakers plus a subwoofer).
- The encoder removes sounds listeners are unlikely to hear and compresses the rest.
- The AC-3 track travels with the video in a stream or file.
- A TV, soundbar or receiver decodes it and sends each channel to its speaker.
AC-3 vs AAC: what is the difference?
AC-3 is mainly used for surround sound on TVs and home theaters, while AAC is the default stereo audio for most streaming. AAC is more efficient at low bitrates and plays almost everywhere. Services often include both: AAC for phones and browsers, and AC-3 or E-AC-3 for living room surround.
Is Dolby Digital the same as AC-3?
Yes, Dolby Digital is the brand name for the AC-3 audio codec. It is also standardized as ATSC A/52. Its successor, Dolby Digital Plus, is known technically as E-AC-3. Both names appear on TVs, receivers and streaming apps, and they refer to the same family of surround sound formats.
Where it's used
OTT services and broadcasters include AC-3 tracks so films, series and sports play in surround sound on living room TVs and home theater systems.
By the numbers
- The AC-3 format was released as the Dolby Digital standard in February 1991. (Wikipedia: Dolby Digital)
- The AC-3 standard allows a maximum coded bit rate of 640 kbit/s. (Wikipedia: Dolby Digital)
