Dolby Digital, Dolby Digital EX, and Dolby Digital Plus

The Dolby Digital Family
Logo provided by Dolby Labs

Surround sound is an integral part of the home theater experience, and with that, there are lots of surround sound formats in use, depending on your audio system's capabilities, speaker layout, and content.

Probably the most used are formats that are part of the Dolby Digital family. In this article, we discuss three of these: Dolby Digital, Dolby Digital EX, and Dolby Digital Plus, which are commonly used on DVDs and Streaming content, and are also present as a supplemental selection in Blu-ray Disc content.

What Dolby Digital Is

Dolby Digital is a digital audio encoding system for DVDs, Blu-ray Discs, and, in some cases, for TV broadcast or streaming content, that provides efficient transfer for audio signals that may be composed of one, or more channels, that can be decoded by a home theater receiver or AV Preamp/Processor with a Dolby Digital decoder and distributed to one or more speakers.

Almost all home theater receivers in use have a built-in Dolby Digital decoder and all DVD and Blu-ray Disc players are equipped with the ability to pass Dolby Digital signals to properly equipped receivers for decoding.

Dolby Digital is often referred to as a 5.1 channel surround system. However, it must be noted that term "Dolby Digital" refers to the digital encoding of the audio signal, not how many channels it has. In other words, Dolby Digital can be:

  • Monophonic- Represented by one or two speakers. However, with two speakers, both reproduce the same the sound, so the sound will appear to come from the space between the speakers.
  • 2-Channel - Represented by two speakers - one on the left and on the right front of the listening position.
  • 4-Channel - Represented by four speakers - Two placed on the left and right front of the listen position, and two on the left and right, and slightly behind the listening position.
  • 5.1 Channels - Represented by five speakers (left, center, right, left surround, right surround), and a subwoofer (.1)

Dolby Digital EX

6.1 Channels - Dolby Digital EX adds a third surround channel that is placed directly behind the listener. Represented by six speakers (left, center, right, left surround, center back, right surround), and a subwoofer (.1.). This brings the total numbers of channels to 6.1.

In other words, the listener has both a front center channel and, with Dolby Digital EX, a rear center channel. If you are losing count, the channels are labeled: Left Front, Center, Right Front, Surround Left, Surround Right, Subwoofer, with a Surround Back Center (6.1) or Surround Back Left and Surround Back Right (which would actually be a single channel - in terms of Dolby Digital EX decoding). A home theater receiver with a Dolby Digital EX decoder is required to access the full 6.1 channel experience.

However, if you have a DVD, or other source content, that contains 6.1 channel EX encoding and your receiver does not have an EX decoding, the receiver will default to Dolby Digital 5.1 can just combine the extra information within a 5.1 channel sound field.

Dolby Digital Plus

7.1 Channels - Dolby Digital Plus is a high definition digital-based surround sound format that supports up to 8-channels of surround decoding, but also contains a standard Dolby Digital 5.1 bitstream that is compatible with standard Dolby Digital-equipped receivers.

Dolby Digital Plus is one of the several audio formats designed and employed by Blu-ray Disc format. Dolby Digital Plus is compatible with the audio portion of the HDMI interface, as well as being applied in streaming and mobile audio applications and is also built into the Dolby Audio platform for Windows 10 and the Microsoft Edge browser.

Although Dolby Digital Plus has its own specific label designation, in many applications, Dolby Digital 5.1 and 6.1 (EX) are often referred to as just Dolby Digital.

Dolby Digital may also be referred to as: DD, DD 5.1, AC3

No matter which format in the Dolby Digital family you have access to, the goal is to provide a room-filling surround sound listening experience that enhances the home theater viewing experience or a fuller audio experience from a compatible PC or portable device.