Handbook for Sound Engineers

754 Chapter 21

Peavey, and Rane. To date, the operational concepts used
in digital automatic microphone mixers have not varied
far from the previously described concepts underlying
the analog automatic microphone mixers. This is likely
to change, but as future digital automatic mixing con-
cepts will be hidden deep within computer code, the
manufacturers may be unwilling to reveal the details of
operational breakthroughs; they will likely be kept as
closely guarded company secrets. New concepts in auto-
matic mixing might only become public knowledge if
patents are granted or technical papers are presented.

The Polycom Vortex EF2280, Fig. 21-26, automati-
cally mixes microphones and other audio sources while
canceling acoustic echoes and annoying background
noise. It is used in boardrooms, courtrooms, distance
learning, sound reinforcement, and room combining. It
connects easily to other equipment including codecs,

VCRs, or other A/V products. The unit can be

programmed from the front panel, or through Confer-

ence Composer™ software (included). Conference

Composer’s Designer™ wizard ensures fast, accurate

setup for a variety of applications.

A single Vortex EF2280 unit provides automatic

mixing of up to eight microphones plus four auxiliary

audio sources. Up to seven additional Vortex EF2280 or

Vortex EF2241 units can be linked to the first unit.

(NOM) information can be specified across all chan-

nels in the linked units. The microphone channels

feature acoustic echo cancellation to prevent retransmis-

sion of signals to their original locations. A neural

network AGC reacts only to valid speech patterns,

bringing voices within desired levels. AGC controls are

user adjustable, as are settings for the five-band para-

metric EQ offered on all input and output channels and

output delay controls. Fig. 21-27 is the block diagram of

the Vortex EF2280.

21.3.4.10 Which Type of Automatic Mixer Works Best?

There is no definitive answer to this question. It is

impossible to tell which automatic microphone mixer

design will operate best in a given situation by studying

technical specifications, believing the marketing litera-

ture, poring over circuit schematics, deciphering lines of

computer code, or rereading this chapter. Human speech

is very complex and human hearing is very discerning.

Like so many areas in professional audio, the critical ear

is the final judge.

21.3.5 Teleconferencing and Automatic

Microphone Mixers

Automatic microphone mixers are used in many tele-

conferencing systems. The design of such systems

involves a number of complex issues that do not enter

into the design of sound reinforcement systems. This

section will discuss important design aspects of such

installations.

As practiced in modern communication between

separated groups of talkers, teleconferencing has two

components—visual and aural. The visual is handled by

television cameras, video monitors, and video projec-

tors. The visual may be full motion in real time, slow

scan, or single-frame presentation.

It is appropriate to identify the aural part of the tele-

conferencing system as the audio conferencing system.

Considerable attention must be paid to a number of

details for acceptable sound quality, intelligibility, and

user comfort. Users of teleconferencing systems tend to

Figure 21-23. Dugan E-1 Automatic Mixing Controller.
Courtesy Dan Dugan Sound Design.

Figure 21-24. The automatic mixing controller is connected
to the insert points of console input channels. Courtesy
Dan Dugan Sound Design.

Console

Microphone

input

Insert

point

Insert

point

Mix

bus

Controller

Control

system

VCA

EQ