Handbook for Sound Engineers

1444 Chapter 38

degrade the quality of the audio. Of course, there are
different degrees of perfection available in SRCs at
correspondingly different levels of complexity and cost.
Some SRCs will only handle incoming digital audio that
is at a precise and simple numeric ratio to the internal
sample rate. Others will accept any incoming sample
rate over a very wide range and convert it to the internal
sampling rate.
This second sort of SRC is very useful when you
must accept digital audio from multiple sources that
have no common reference, and convert them all to a
common internal sampling rate.
As implied above, the other way to handle inputs
from multiple digital audio sources is to lock all the
devices in the digital audio system to a common refer-
ence sample rate. In large systems this is the preferred
solution, and the Audio Engineering Society has devel-
oped the AES11 Standard, which explains in detail how
to properly implement such a system. Such a system can
have excellent jitter performance since each device
directly receives its sampling rate reference from a
common source. Interconnections between the digital
audio devices can be rearranged freely since we do not
have to be concerned about synchronization and jitter
changes as the signal flow is changed.
The only flaw in this scheme, is that some digital
audio devices may not have a provision for accepting an
external sampling rate reference. As a result, in many
complex systems while there may be a master sample
rate clock that most equipment is locked to, there often

is still a need for samplthat can’t lock to the master

clock, or that operate at a different sample rate.

38.2.3.6 Multifunction Devices

Once we grouped most or all of our digital devices in a

single subsection of our system, the next natural question

is why not combine these multiple separate devices into a

single product. Obviously, such a combined device

greatly reduces or eliminates the need for the system

designer to be concerned with synchronization issues,

since the equipment designer has taken care of all the

internal issues. Only if the system contains more than one

digital audio device with digital interconnections does the

issue of synchronization arise.

Some of the first examples of such combination prod-

ucts were digital mixers and loudspeaker processors.

Digital mixers were developed that combined not

only the traditional mixing and equalization functions,

but also often added reverb and dynamics processors

inside the same device. Depending on the intended

application, such digital mixers might also integrate

automation systems, and remote control surfaces.

Remote control surfaces allow the separation of the

signal processing from the human operated controls.

This might allow all the signal processing to remain on

stage, for example, while only the control surface is

placed at the operator’s position, Fig. 38-2.

Figure 38-2. The CueConsole from Level Control Systems is a modular audio control surface. The size of the control surface

has no direct relationship to the number of audio inputs and outputs controlled. The actual audio processing is performed

in Matrix3 processors (lower right corner) located remotely from the control surface. These systems are very popular for

Broadway- and Las Vegas-style shows since very large and powerful automated consoles can take up very little of the valu-

able space in the theater.