Dolby Digital Plus
Dolby Digital Plus, also known as Enhanced AC-3 (and commonly abbreviated as DDP, DD+, E-AC-3 or EC-3), is a digital audio compression scheme developed by Dolby Labs for the transport and storage of multi-channel digital audio. It is a successor to Dolby Digital (AC-3), and has a number of improvements over that codec, including support for a wider range of data rates (32 kbit/s to 6144 kbit/s), an increased channel count, and multi-program support (via substreams), as well as additional tools (algorithms) for representing compressed data and counteracting artifacts. Whereas Dolby Digital (AC-3) supports up to five full-bandwidth audio channels at a maximum bitrate of 640 kbit/s, E-AC-3 supports up to 15 full-bandwidth audio channels at a maximum bitrate of 6.144 Mbit/s.
"DD+" and "DD Plus" redirect here. For the bra size, see Bra size.MIME / IANA
Encapsulation, use, and storage of Dolby Digital streams[edit]
Physical transport for consumer devices[edit]
IEC 61937-3: defines how to transmit Dolby Digital (AC-3) and Dolby Digital Plus (E-AC-3) bitstreams via an IEC 60958/61937 (S/PDIF) interface. However, the S/PDIF interface has insufficient bandwidth to transport Dolby Digital Plus (E-AC-3) bitstreams at the 3.0 Mbit/s datarate specified by HD DVD; lower datarates are possible.
Much consumer gear, and even some professional gear, does not recognize Dolby Digital Plus as an encoded format, and will treat DD+ signals over a S/PDIF or similar interface, or stored in a .WAV file or similar container format, as though they were linear PCM data. This is not problematic if the data is passed unchanged, but any gain scaling or sample rate conversion, operations which are aurally harmless to PCM data, will corrupt and destroy a Dolby Digital Plus stream. (Older codecs such as DTS or AC-3 are more likely to be recognized as compressed formats and protected from such processing).
Dolby Digital Plus may be transmitted across HDMI 1.3 or newer, according to IEC 61937-3.
Physical transport for professional devices and applications[edit]
As the AES-3 interface is the professional analog to S/PDIF, Dolby Digital Plus streams may be carried over AES-3 connections with sufficient bandwidth, and/or over other interfaces that encapsulate AES-3 (such as SMPTE 259M and SMPTE 299M embedded audio). Additional standards promulgated by SMPTE specify the encoding of Dolby transports, including Dolby Digital, Dolby Digital Plus, and Dolby E (a professional-only codec used in audio/video applications) on an AES interface. The SMPTE 337 standard specifies the signalling and carriage of signals that are not PCM audio over an AES-3 interface, and the SMPTE 340-2008 standard specifies how Dolby Digital Plus and Dolby Digital are to be transmitted over that interface. The combination of SMPTE 340-2008 and 337M allow the Dolby Digital Plus bitstream to be stored and transported within professional production, contribution and distribution workflows prior to emission to consumers.
Consumer broadcast in digital television systems[edit]
Either DD+ or Dolby Digital is specified by the Advanced Television Systems Committee as the primary audio codec for the ATSC digital television system, and is commonly used for other DTV applications (such as cable and satellite broadcast) in countries which use ATSC for digital television.
For broadcast (emission) to consumers, the Dolby Digital Plus bitstream is packetized in an MPEG elementary stream, and multiplexed (with video) into an MPEG Transport Stream. In ATSC systems, the specification for carrying Dolby Digital Plus is described in ATSC A/53 Part 3 & Part 6. In DVB systems, the specification for carrying Dolby Digital Plus is described in ETSI TS 101 154 and ETSI EN 300 468.
Dolby Digital Plus is seeing increasing use in digital television systems, particular in cable and satellite systems, as a replacement for Dolby Digital. Many such applications don't take advantage of its higher channel count or ability to support multiple independent programs; instead it is used as a higher-efficiency codec than AC-3.