Issuu on Google+

Encoding and Embedding of Dolby-E

GEP100 - HEP100

3Gb/s, A HD, description SD embedded of howdomain to encode Dolby audio E toinPCM the Dolby-E format and decoder embed with it into audio SDI shuffler video A

A

®

® product application note

Quad speed

Upgradable to

3Gb/s Embedded

Metadata S2020

COPYRIGHT©2011 AXON DIGITAL DESIGN B.V. ALL RIGHTS RESERVED NO PART OF THIS DOCUMENT MAY BE REPRODUCED IN ANY FORM WITHOUT THE PERMISSION OF AXON DIGITAL DESIGN B.V.


EMBEDDED AND ENCODING AUDIO EMBEDDING PROCESSING OF DOLBY-E

Introduction The use of Dolby-E encoding gives broadcasters and facility operators the ability to embed up to 64 audio channels into a single SDI video: 2 Dolby-E streams in each of the 4 audio groups with each stream having a maximum capacity of 8 mono audio channels.

prior to the final digital transmission, and then reencoded into the final audio format as required by the intended distribution platform. Possible Dolby E program configurations could include:

An example of the utilisation of this is where a broadcaster is producing a transmission feed mixed in 5.1 surround sound with an associated stereo mix intended for reception in multiple territories, with each territory requiring their own local language. By encoding each surround and associated stereo mix in Dolby-E it is possible to include 8 languages in the SDI video which could then be passed through the playout path in the conventional manner.

▪▪

The Dolby E signal is not intended for distribution usage; it is decoded back to baseband audio just

▪▪

▪▪ ▪▪ ▪▪ ▪▪ ▪▪

5.1 - 5 full range surround audio channels + a band limited low frequency effects channel 5.1+1+1 – 5.1 surround sound channels + 2 mono channels which could be used for audio description 5.1+2 – 5.1 surround sound channels + 1 stereo channel which might be used for an alternative two-track version of the surround sound mix 6×1 – 6 mono channels 8×1 – 8 mono channels 3×2 – 3 stereo channels 4×2 – 4 stereo channels

Alignment of Dolby-E in Video Systems Dolby E streams include audio and metadata encoded into blocks of SMPTE 337M data, streamed on a discrete AES/EBU channel or embedded into SDI. As the Dolby E bit-stream is normally carried along with video these data blocks are output at a rate associated with a chosen video frame rate. Possible video frame rates are: 29.97 fps (NTSC); 25 fps (PAL); 23.98, 24, 30 fps. The Dolby E specification also ensures that the audio frames are synchronous with video frames, enabling programmes to be switched and edited without having to decode and recode the audio.

called the “Line Position.” This relates to a specific video line to which the start of the Dolby E data is aligned.

To allow error-free “cuts only” editing and video source switching in routers, a short period in each frame has silent samples around the point in the stream at which the edit or video switch is intended to occur, this period is known as the guard-band. The point of where the guard band ends and the SMPTE 337M Dolby E data burst starts is often

▪▪ ▪▪ ▪▪ ▪▪ ▪▪ ▪▪

The ideal location of a Dolby-E frame is so that it starts after the video switching point and it finishes before the end of the video frame. The location of the Line Position to place the Dolby-E frame in the centre of the video frame is 730µS after the start of the video frame, this can be safely varied by 80µS. The actual line that this timing is related to depends on the video standard being utilised: 625i25 (SD PAL), Line 12 720p50 (HD PAL), Line 28 1080i50 (HD PAL), Line 21 525i30 (SD NTSC), Line 14 720p60 (HD NTSC), Line 32 1080i60 (HD NTSC), Line 26


EMBEDDED AND ENCODING AUDIO EMBEDDING PROCESSING OF DOLBY-E

Synapse Card Reference Selection and Video Timing The importance of correct system timing is critical in building a system that will successfully encode and embed Dolby-E within a SDI stream. The Dolby-E frames need to be generated at the same frame rate as the video they are to be embedded into and these frames need to be correctly aligned with the video frames. Synapse cards provide the necessary functionality and selection choices to allow this to reliably occur. The diagram below shows a typical scenario where a HD-SDI signal containing 5.1 surround audio is deembedded using a HDB990, the three resultant AES streams are encoded via a DBE08 and the Dolby-E frames reembedded using a HEB880. In addition to de-embedding the HDB990 card also has a delay function which is used to synchronise the video with the Dolby encoded audio following the 1-frame processing delay. The diagram shows the DBE08 Dolby encoder card connected to the embedder via the Synapse Bus which requires the card to be located immediately to right of the embedder in the same frame, this has the advantage that all of the connections are taken care of without external cables and also the various clocks on the Dolby encoder are locked to the video source via the MasterCard signal carried on the bus. Up to four DBE08 cards can be connected in this manner each inserting the Dolby-E stream onto tracks 1/2 of successive SDI audio groups, these can then be repositioned to the desired tracks in the output SDI stream using the audio shuffler functionality on the

HEB880 embedder card. If locating the Dolby-E encoder card next to the embedder in not practicable, or there is a requirement for more than four Dolby-E streams, cards can be connected using external balanced or unbalanced AES cables, in which case the card would be locked to an external reference synchronised to the video into which the Dolby-E encoded audio was to be embedded. The DBE08 Dolby-E encoder uses the reference signals distributed throughout the Synapse frame to determine where a Dolby frame should start and stop, therefore it is critical that the video into which the Dolby-E frames are to be embedded is referenced to the same source as the Synapse frame. The video should be timed so that it is synchronous with the reference signal at the input of the embedder, this can be achieved by adjusting the source’s timing or changing the amount of delay introduced into the video signal by the HDB990 de-embedder card. It should be noted that none of the cards in this system provide framesync functionality, if the source to the system is expected to change or its timing cannot be fixed than Axon recommend placing a synchroniser (such as the HFS010) in the video path before the de-embedder card. By adopting this methodology Dolby-E frames produced by the DBE08 card will be correctly inserted within the video frame on the embedder card. Further adjustment of the Dolby-E frame timing can be achieved using the Guard Band Delay control on the DBE08 card, this can add an additional 625-lines of delay to the Dolby-E frames.


Video with 5.1 surround sound on discrete tracks 1 to 6

3Gb/s, HD, SD IN 2

3Gb/s, HD, SD IN 1

1

AUTO MUX

2x1 OR 2x2

PLL

REFERENCE INPUTS 2

S2020 READER

RAIL 2 16 CHANNEL DE-EMBEDER

RAIL 1 16 CHANNEL DE-EMBEDDER

AUTO PHASER

AUTO PHASER

RAIL 2

RAIL 1

Eq

Eq

B

A

ADJUSTABLE OFFSET DELAY 0-500ms

A

B

A = SINGLE CHANNEL B = DUAL CHANNEL

2

3

4

INTERNAL SYNAPSE BUS

1

4 Ch 4 Ch 4 Ch 4 Ch

32X32 CHANNEL MULTIPLEXER

POST DELAY 2

AUDIO OUTPUTS TO SYNAPSE BUS

16 Ch

16 Ch

PRE DELAY 2

ADJUSTABLE OFFSET DELAY 0-500ms PRE DELAY 1 POST DELAY 1

GDB990 – HDB990 - GDB900 – HDB900

Delay = 1 Frame to match the Dolby-E encoding delay

µP

RACK CONTROLLER

AES/EBU OUTPUT 8

DELAY GAIN/PHASE

GPI/O

AES/EBU OUTPUT 7

DELAY GAIN/PHASE

G/HDB990 ONLY

AES/EBU OUTPUT 6

AES/EBU OUTPUT 5

DELAY GAIN/PHASE DELAY GAIN/PHASE

AES/EBU OUTPUT 4

AES/EBU OUTPUT 3

DELAY GAIN/PHASE DELAY GAIN/PHASE

AES/EBU OUTPUT 2

AES/EBU OUTPUT 1

METADATA

3Gb/s, HD, SD OUT 2

3Gb/s, HD, SD OUT 1

METADATA

GPI

AES 7/8

AES 5/6

AES 3/4

AES 1/2

G/HEB880 ONLY

AES/EBU INPUT 8

AES/EBU INPUT 7

AES/EBU INPUT 6

AES/EBU INPUT 5

AES/EBU INPUT 4

AES/EBU INPUT 3

AES/EBU INPUT 2

AES/EBU INPUT 1

3Gb/s, HD, SD IN 1

SRC

SRC

SRC

SRC

SRC

SRC

SRC

SRC

1

DBE08

Eq

2

SRC

SRC

SRC

SRC

GENERATOR

GAIN CONTROL

CHANNEL SWAP

1

3

4

2

3

4

3

2

BY-PASS DELAY

DARS GENERATOR

ENCODER

INTERNAL SYNAPSE BUS

1

EMB B

AUDIO INPUTS FROM SYNAPSE BUS

4 Ch

4 Ch

4 Ch

4 Ch

EMB A

INTERNAL SYNAPSE BUS

2

4 Ch 4 Ch 4 Ch 4 Ch

PRESET BASED 32X16 CHANNEL (24X16 FOR G/HEB800) INPUT MULTIPLEXER FOR EVERY EMBEDDER GROUP

Audio in/outputs To/from Synapse bus

PLL

DELAY

DELAY

DELAY

DELAY

DELAY GAIN/PHASE

DELAY GAIN/PHASE

DELAY GAIN/PHASE

DELAY GAIN/PHASE

DELAY GAIN/PHASE

DELAY GAIN/PHASE

DELAY GAIN/PHASE

DELAY GAIN/PHASE

GEB880 - GEB800 - HEB880 - HEB800

System Schematic

DELAY GAIN/PHASE

DELAY GAIN/PHASE

ENCODING AND EMBEDDING OF DOLBY-E

1

EMB C

µP

RACK CONTROLLER

µP

Rack controller

+

CHANNEL 3/4 [AUX] SELECTION

AES/EBU FORMAT

AES/EBU FORMAT

MAIN OUTPUT SELECTION

EMB D

AUX OUT

DOLBY E OUTPUT

GPI/O

3Gb/s, HD, SD OUT 2

3Gb/s, HD, SD OUT 1

Video with Dolby-E encoded audio


EMBEDDED AND ENCODING AUDIO EMBEDDING PROCESSING OF DOLBY-E

Dolby-E Line Prosition Alignment Process

▪▪ ▪▪ ▪▪

▪▪

Connect cards as shown on the previous page ensuring the Synapse frame has at least one external reference connected Determine if the timing of the input video may change – if yes install frame synchroniser prior to de-embedder Set the HDB990 Lock-Mode to the internal reference buses which has an external reference connected i.e. Ref1. Ensure the Ref-Input of the DBE08 Dolby-E encoder is set to the same reference source. If the DBE08 is connected to the embedder by the Synapse Bus select LockMode to be MasterCard, otherwise select Reference.

▪▪

▪▪

Using the Measurement option on a Tektronix 7120 WFM or similar adjust the timing of the video source to the HEB880 embedder to be synchronous with the reference +1 frame (to allow for the delay in the Dolby encoding process). This can be achieved by timing the source video prior to the de-embedder or using the delay functionality of the de-embedder card. Check the positioning of the Dolby-E data within the video output from the HEB880, use the Guard-Band Shift function on the DBE08 card to delay the frames if required.

Card Settings The following tables give examples of the configuration options required to successfully encode and embed Dolby-E into a SDI stream, please note that the cards have considerably more settings than shown here and these should be set to match the user’s individual requirements.

HDB990 Settings

Notes

Lock-Mode

Ref1

The card should ideally be referenced to the same external reference as the DBE08 Dolby-E encoder

F-Delay_1

1F

Video delayed by I frame to compensate for the delay through the Dolby-E encoder

H-Delay_1

2 ln

It may be necessary to add additional delay so that the HEB880 input video is synchronous with the external reference

Delay-Status

On

Turns delay delay monitoring in the status tab on

#SourceLocA1

Rail1

Selects the video source for local de-embedded AES outputs

#LocOutA1

Ch_1

Selects which SDI track to output on the local outputs The de-embedder settings are repeated for all used audio outputs, in this example A1 – A6

DBE08 Settings

Notes

LockMode

MasterCard If the Dolby-E output is connected to the embedder by the Synapse Bus using MasterCard will lock the DBE08’s clocks to the embedder

Ref-Input

Ref1

The Ref input is used to determine Dolby-E frame position and should be the same selection as the Lock-Mode on the HDB990

DolbyE Depth

20 bits

Selects the number of bits used by the Dolby encoding process

Prgm

5.1 A

Selects the channel line-up in the Dolby-E encoder, the letter refers to the predetermined metadata to be associated with the Dolby-E Stream

Dolby-CH_1

AES_1

Selects which AES input (1 to 8) will be used as the source for each channel to be encoded. This setting is repeated for each Dolby channel in use

GD_Shift

2 line

Sets the amount of additional delay is applied to the Dolby-E output so that it Guard-Band is correctly positioned relative to the video the streamed is to be embedded into


EMBEDDED AND ENCODING AUDIO EMBEDDING PROCESSING OF DOLBY-E

Card Settings The setting below would embed a Dolby-E stream into tracks 1/2 of the SDI, similar configuration options are provided for the other SDI tracks

HEB880 Settings

Notes

NoPCM-Bypass

On

This will bypass audio process of non-PCM signals such as Dolby-E

#SourceEmb-A1

AddOnA

Selects the AddOnA (Synapse Bus A) as the source of the audio to be embedded

#Emb-A1

Ch_1

Selects Ch_1 from AddOnA as the source for embedding into Group A track 1

#SourceEmb-A2

AddOnA

Selects the AddOnA (Synapse Bus A) as the source of the audio to be embedded

#Emb-A2

Ch_2

Selects the video source for local de-embedded AES outputs


AN2011-04 Encoding and embedding of Dolby-E.pdf