Dolby Digital Plus is lossy audio encoding scheme and an extension to Dolby Digital introduced in 2004, which allows for a much wider data rate compared to the standard AC-3 encoding scheme (Dolby Digital Plus is also known as Enhanced AC-3, or E-AC-3), up to 6.0 Mbit/s along with more channels at the same bitrate, with a maximum of 15 channels for a 15.1 channel configuration. It is based on a modified version of the original modified discrete cosine transform (or MDCT) along with additional exclusive techniques for encoding audio such as the Adaptive Hybrid Transform (AHT for short), Enhanced Coupling (ECPL), and more involved spectral extensions; among several others.
It was selected for use in the ATSC digital television system in the late 2000s and early 2010s alongside its precursor; and was also selected as a mandatory format for the now-defunct HD-DVD format with a maximum of 7.1 channels at a 3.024 Mbit/s bitrate maximum, as well as an optional format for the Blu-ray format - however, for most of the format's life, E-AC-3 was only permitted for rear channels in a 6.1 and 7.1 configuration at 1.664 Mbit/s bitstreamed into a regular 640 kbit/s Dolby Digital stream. However, the newer Ultra HD Blu-ray format began to relax these restrictions, and is now sometimes seen as a lossy fallback or as the encoded format for other languages in some recent releases.
Due to the latter format's heavy limitations on E-AC-3 along with the failure of the HD-DVD format and its lossy nature, Dolby Digital Plus remains one of Dolby's lesser known audio formats, and was overshadowed by the lossless Dolby TrueHD unveiled at around the same time. Nonetheless, Dolby Digital Plus streams live on in the streaming world as some services such as Vudu make use of the format for their audio support. Additionally, Dolby Atmos spacial audio streams can be bitstreamed onto a DD+ stream as the newer format's lossy implementation (which is what some streaming services use as part of their support for Atmos), sometimes referred to as Dolby Digital Plus with Atmos.
Trivia[]
Original logo design
- The very first media to make use of a Dolby Digital Plus track are HD-DVD's launch titles, such as Serenity and The Last Samurai - on April 18th, 2006.
- As of 2022, some Disney UHD releases make use of DD+ streams for additional languages, among a few others.
- E-AC-3 and TrueHD streams are not compatible with one another despite them both being introduced in 2004 and released in 2006 - the latter only maintains a standard DD fallback layer.