Dolby Laboratories DM100 Manual de usuario descargar pdf (Pagina 23)

Dolby Model DP583 Frame Synchronizer User’s Manual Applications

3-3

DAT

DP583

AES and Video

Reference

Generator

Dolby E data

locked to

video

reference

AES Ref In

Output Main Input

Video Ref

Main Output

AES

Video

Figure 3-3 Post Production Application

3.3 Dolby Digital (AC-3) Application

Many digital broadcast encoder and uplink systems now have the ability to accept a

pre-compressed Dolby Digital (AC-3) bitstream from an "external" multichannel

Dolby Digital encoder such as the DP569 (as per SMPTE 337M and SMPTE 340M).

However, there are applications in which the Dolby Digital (AC-3) bitstream is not

directly sourced from the Dolby Digital encoder but from an IRD (Integrated

Receiver Decoder) instead.

One example is a DBS or cable turn-around facility that requires the pre-compressed

Dolby Digital bitstream be passed (i.e., without decoding to PCM) through its facility.

A potential problem comes with different time bases between the decoded and locally

frame-synchronized video and the “asynchronous” pre-compressed Dolby Digital

bitstream being fed to a downstream encoder and multiplexer. See Figure 3-4.

In the past broadcast facilities have employed the use of audio sample rate converters

to synchronize the incoming audio to a local clock (usually 48 kHz AES Ref):

however, traditional audio sample rate converters are not compatible with non-PCM

audio data (e.g., Dolby Digital (AC-3), Dolby E) carried over an AES3 interface.

Note that the application in Figure 3-4 depicts two IRDs. One is for passing the

decoded video and audio, which is "locally" frame synchronized, to the local encoder

and multiplexer. The second IRD is used to provide access to the Dolby Digital (AC-

3) bitstream to complete our pass-through scenario. Some IRDs are able to decode the

video and audio and simultaneously pass the Dolby Digital bitstream; however, this

still requires that the Dolby Digital (AC-3) data be synchronized to the local facility

reference using the DP583.

MAIN

1 2 ... 18 19 20 21 22 23 24 25 26 27 28 ... 35 36

Sin comentarios

Dolby Laboratories DM100 Manual de usuario Pagina 23