Handbook for Sound Engineers

982 Chapter 25

useful for the control surface to display. This is usually
a sizable and capable processor, unless its functions are
being done by a PC’s CPU.

Audio Processing. This uses the coefficients from the
processing host to modify the audio path(s) as desired,
usually within a raft of DSPs, either aided by or
supplanted by FPGA’s, unless, of course, the audio
processing is within a PC’s CPU.

Routing Assignment. Decides what audio path is going
to get routed through what path within the audio
processing and so what controls apply to it. Also decides
on what output ports processed audio appears. Often an
additional soft matrix done in a DSP mixer (particularly
when integrated with Audio Processing), or a hard
switch in FPGA, and often a stand-alone product but
entirely within the capabilities of a PC’s CPU.

Audio Input Output. This is the termination of audio
sources and destinations and their conversion into a
form of digital information the Audio Processing can
assimilate. Examples are A/D and D/A converters,
usually many, and SRCs (Sample Rate converters) to
seamlessly integrate external digital audio sources.
Often stand-alone, in cages dedicated to their purpose,
locally or separated from the rest of the system. Often
integrated with the Routing/Assignment, and sometimes

along with audio processing. And sometimes just

plugged straight into a PC. (Bet you can’t guess where

this is going...)

The paths between any of these blocks may be

broken and subject to transport if need be, but it is far

more likely by way of practicality at labeled junctures B,

E, and F; for instance, it is generally easier to transport

the rendered, lower data concentrations of control

parameters and meter data between the Surface and

processing hosts at (B) than it would be to try to move

the raw preprocessed metering data and coefficient sets,

as would be the case if a split were made at juncture (D).

Nearly any audio console with digital control fits

into this loose model and contains all these elements in

some form or other; even a DCA (digital control of

analog) console, with a control surface separated from

the processing electronics at interface B, is similar to

case (1), a normal console. So it can be seen that the

lineage from analog consoles, through DCA, pure

digital consoles (which at least initially mirrored analog

consoles almost totally), through to DAWs is quite

plain.

The subdivisions of these processing blocks for

different classes of console, and with likely transport

means, are shown in Fig. 25-151:

Figure 25-151. Process distribution in various styles of digital mixers.

A B C D E F G

Surface

Meters

Controls

Surface

Host

Processing

Host

Metering

Coefficients

Audio

Processing

Routing

Assignments

Audio

Input/

Output

1. Normal Console:
   Control surface Ethernet Mixing Router


2. Distributed Console:
   Surface Ethernet Mixer Ethernet Router

3 Stand-alone Console

Self-contained hardware

4 DAW with I/O

Self-contained in PC USB I/O

5 DAW with Surface

Surface MIDI USB I/O

6 Simple DAW

All within PC