Dolby Laboratories DM100 Bedienungsanleitung PDF herunterladen (Seite 21)

3-1

Chapter 3

Applications

This section presents common broadcast and postproduction audio applications for

the DP583 Frame Synchronizer.

3.1 Dolby E Distribution or Backhaul Application

Dolby E has become a widely accepted format for broadcasters wanting to easily

distribute multichannel and multi-program digital audio. However, the seamless

switching and editing properties of Dolby E rely on the proper phase synchronization

of Dolby E frames relative to video frames. Dolby E encoders will produce Dolby E

frames with a specific alignment of phase with respect to the local video reference.

Equipment that passes the Dolby E signal is expected to maintain this phase

relationship to within a certain tolerance. A term that is often used in the context of

Dolby E phase synchronization is guard band, which refers to the number of audio

sample locations that do not contain Dolby E audio data around the defined video

switch point. The guard band is intended to be aligned with the vertical interval

switch points of video as defined by SMPTE RP168 and is also restricted to odd-

fields, allowing the Dolby E data to be switched without corruption.

Since this phase relationship or guard band alignment is critical for broadcast

distribution applications it becomes necessary, under certain circumstances, to re-

align the Dolby E data (i.e., frames) using a local video reference at a destination

facility (e.g., a live feed to a network station, or network to an affiliate or local

station) without having to decode and re-encode it. For example, the DP583 Frame

Synchronizer allows the affiliate station to properly phase align incoming Dolby E

data relative to the local video reference generator before presenting the data stream

to their routing switcher.

This process is similar in concept to what many broadcast facilities currently do with

incoming video signals. For this application, a video frame synchronizer is used to

allow the affiliate station to “re-time” and thus reframe the video signal relative to its

local reference generator, giving them the ability to switch to the incoming feed

cleanly without picture shifts.

Figure 3-1 illustrates properly phase aligned Dolby E frames with associated video

frames. Notice the Dolby E guard band in this case is located at the defined

switching/edit location for each video frame. In this case, a frame based audio-follow-

video switch adhering to SMPTE RP168 will result in no Dolby E data being

corrupted.

MAIN

1 2 ... 16 17 18 19 20 21 22 23 24 25 26 ... 35 36

Keine Kommentare

Dolby Laboratories DM100 Bedienungsanleitung Seite 21