Dolby E Basics

Dolby E is a digital audio compression technology designed for use by TV broadcast and production professionals in and among their facilities.

It allows an AES/EBU (Audio Engineering Society/European Broadcasting Union) audio pair to carry up to eight channels of digital audio and Dolby Digital metadata. Audio can be edited without mutes or clicks and can be encoded and decoded multiple times without audible degradation.

Metadata is additional control information that is carried along with the encoded audio program and provides essential information about the audio to a decoder. Metadata provides many important functions including dynamic range control for less-than-ideal listening environments, level matching between programs, down mixing information for the reproduction of multi-channel audio through fewer speaker channels, and other information. Metadata makes Dolby Digital and Dolby E a complete delivery system for audio, rather than just an audio compression system.

The maximum channel count is 8 channels and 24 programs. A program is a grouping of audio channels intended for consumer delivery such as stereo, 5.1, or multi-language versions of the same material. A channel is simply the placeholder for an individual audio file. Channels assembled equal the various programs for delivery.

The maximum essence resolution is 20 bits at 48 kHz sampling rate.

Dolby E is used in broadcast and post-production facilities to distribute multi-channel audio, six or eight channels, through a two-channel transport system. This occurs where there are equipment limitations, such as the number of tracks on a VTR for example, or where bandwidth requirements make multi-channel audio costs prohibitive such as with satellite capacity. Dolby E gets multi-channel audio to TV affiliate stations, so that they can transmit a multi-channel signal to consumers using Dolby Digital. Note that Dolby E audio never reaches the viewer at home. Like all DTV audio, it is decoded to PCM audio and then re-encoded into Dolby Digital just prior to transmission.

With DTV systems, consumers can receive 5.1 channel digital audio in their homes via Dolby Digital broadcasts. The problem is that most TV broadcast infrastructure can handle only two-channel digital audio. Dolby E provides the networks and cable systems a method for getting 5.1 channel digital audio through their two-channel systems.

As a format, Dolby E is sprinkled throughout the industry. In the western markets, the most prevalent being remote trucks and archival work. Dolby E can carry and maintain Dolby Digital metadata (DD being require for digital television delivery in The States), so trucks can prep and ingest content – and the metadata can instruct a downstream DD encoder on how to behave– prior to playout. There is also a lot of older content that lives on tape too. Archival departments are using our software solution in place of Dolby hardware, when laying back from VTR to Pro Tools, Media Composer, etc. Eastern markets jumped from mono to surround in a manner of months about 2 years ago, and Dolby E has been quite popular in their broadcast and post areas. There are other use cases, but these are the most prevalent.  

Most of the spigots in the world are still 2-channel (Analog, AES, etc.), so mezzanine codecs like Dolby E remain relevant. This goes away to some degree with AES67 and AOIP as a whole, but most of the world isn’t there yet, and there is a lot of content that exists in Dolby E and similar formats.

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