Grass Valley CR Series v.3.2 - Manual (Page 30)

18
Introduction
Overview
Digital Audio Routers
(See CR6400 Routers on page 16 for a discussion of the CR6400 family’s AES router. This section
does not apply to the CR6400 family.)
Other digital audio routers are discussed here.
The 1RU AES routers have 16×16, 16×4, or 8×8 crosspoints. The 2RU AES routers have either
32×32 or 32×4 (stereo) crosspoints.
Figure 2-23 is a simplified view of an AES router:
Fig. 2-23: Block Diagram of the AES Router
If a video reference is present, the router is considered “synchronous” and regenerates output at
48kHz (nominally). The routers also perform a certain amount of signal processing if the input is
synchronous. If a video reference is not present, the router is asynchronous and passes input
signals straight through without any processing.
In synchronous mode, the router can perform mono routing, in which case, the maximum
number of signals is 2N, that is 8, 16, 32, or 64. In asynchronous mode, the router processes AES
stereo pairs.
The “AES” routers switch AES3id audio. The AES routers switch in sync with a video reference if
one is present.
The two AES modes have different functional characteristics:
• Synchronous mode.
This mode is intended for 48kHz input. However, the router accepts input from 32kHz to
192kHz. The router produces AES3id output at 48kHz using adds and drops,
1
as required. If
the input itself is locked to the video reference, no adds or drops occur.
The 16×16 router supports either 16×16 stereo switching or 32×32 mono channel switching
(when controlled by an external control system). The 32×32 router supports either 32×32
stereo switching or 64×64 mono channel switching (when controlled by an external control
system). Refer to
AES Routers on page 181 for more information.
M N
μP Logic
Inputs Outputs
Crosspoint
Switch
Control
Panel
Video Refer-
ence
Serial
Ethernet
(optional)
M = 8, 16 or 32
N = 4, 8, 16, or 32
1. When the source and output AES streams are not in sync, AES samples arrive at a rate different from the
rate at which they leave the router. Add: when the source is slower than the output, router software oc-
casionally inserts an extra copy of the most recent sample in the output stream until the source and
output are back in sync. Drop: when the source is faster than the output, software occasionally does not
send the sample(s) to the output until the source and output are back in sync again. Adds and drops are
performed on a minute scale, never in large blocks, keeping perceptible distortions to a minimum.