Dolby E
Dolby E is a digital audio coding method from Dolby , which is used in broadcasting stations , especially television stations and post-production studios , for the transmission and storage of audio material. It enables the transmission and storage of up to eight discrete audio channels in standardized data streams according to AES-3id , as they are usually provided for the transmission of a stereo signal with two audio channels in the form of PCM audio . The transmission of Dolby E within the AES-3 infrastructure takes place according to the recommendation SMPTE 337M. Dolby E allows the transmission or storage of up to 8 mono channels (8 × 1.0), 4 × stereo 2.0 or surround sound in 5.1 format and stereo 2.0 at the same time. The number of possible channels depends on the word length of the recording or transmission system: 6 channels with 16 bits, 8 channels with 20 or 24 bits. The recording or transmission can take place with any bit-transparent medium, such as digital video machines, satellite uplinks, servers or editing systems.
The coding is based on proprietary and only slightly lossy audio data compression . Dolby E is acoustically transparent and the quality is well above Dolby Digital ( AC-3 ). Depending on the configuration, the data rate is 1536 kbit / s (with 16 bit word width of the medium) or 1920 kbit / s (with 20 bit) and is thus about five times as high as with Dolby Digital (384 or 448 kbit / s). While methods such as Dolby Digital can only survive about three coding-decoding cycles, Dolby E allows up to about 13 such cycles and is therefore also suitable for multiple processing of audio material in the course of transmission and post-processing. Dolby E is transcoded to Dolby Digital or other methods before being broadcast on TV stations or during disc mastering of DVDs and Blu-Ray discs. As with Dolby Digital (and to a limited extent with DTS), so-called metadata is transmitted parallel to the actual audio signal . This includes information on loudness (Dialogue Level, DialNorm Value), information on controlling the dynamic range (Dynamic Range Control, DRC) and for automatic downmixing from 5.1 to Stereo (Lo, Ro) or ProLogic II (Lt, Rt). These controlling and descriptive metadata are set during production (metadata editing) and passed on from Dolby E to Dolby Digital. The task of the metadata is to adapt the playback in the home device to the respective playback conditions as well as the loudness control . Dolby E metadata are standardized according to SMPTE RDD6.
An essential feature of Dolby E is that the length of the audio frames corresponds exactly to the associated video image. Images in the television technology in the form of a temporal sequence of frames (engl. Frames transmitted): For PAL 25 frames per second, which is 40 ms per image, in NTSC 29.97 frames per second and 33.37 ms per image. For the time of a full picture , for example 40 ms, with Dolby E the associated sound is encoded by up to eight channels and assigned to this video frame. This means that no lossy recoding of the associated audio signal has to take place in television studios, for example when editing or transferring images. The audio data that is permanently assigned to a specific video image, such as the video data, can thus be cut or switched. When using Dolby Digital or other methods in the studio, a repeated sequence of coding and decoding of the audio signals would be necessary, which would reduce the audio quality due to the lossy compression. Although Dolby E is not officially standardized as a norm, due to its widespread use it is considered the de facto standard for the production and transmission of multi-channel sound (production or distribution bitstream).
literature
- Society of Motion Picture and Television Engineers: RDD 6, Description and Guide to the Use of the Dolby E Audio Metadata Serial Bitstream . SMPTE, 2006.
- Society of Motion Picture and Television Engineers: SMPTE 337M, Format for Non-PCM Audio and Data on an AES3 Serial Digital Audio Interface . SMPTE, 2000.
- Michael Dickreiter, Volker Dittel, Wolfgang Hoeg, Martin Wöhr (eds.), "Handbuch der Tonstudiotechnik", 8th, revised and expanded edition, 2 volumes, publisher: Walter de Gruyter, Berlin / Boston, 2014, ISBN 978-3- 11-028978-7 or e- ISBN 978-3-11-031650-6 .
- Stefan Weinzierl (Ed.): Manual of audio technology, chap. 11 . Springer, 2008.
- Dolby: Standards and Practices for Authoring Dolby® Digital and Dolby® E Bitstreams, Issue 3 . Dolby, 2002 ( Standards and Practices for Authoring Dolby® Digital and Dolby® E Bitstreams, Issue 3 ( Memento from December 6, 2003 in the Internet Archive ) [PDF]).
- Karl M. Slavik (ARTE CAST) and Will Kerr (DOLBY): Timing and Time Alignment for Dolby E . 2009 ( artecast.com [PDF]).
Web links
- Dolby E. Dolby Laboratories, accessed May 30, 2016 .