7
English --
OPERATING PRINCIPLES
The AMS8100 is designed for use in a wide variety of mul-
tiple microphone speech applications. It is an audio processor
that activates only the microphones that are being addressed.
The operational concept behind the AMS8100 is called
Direc-
tional IntelliMix
Ò
. It delivers seamless automatic mixing via a
unique combination of features:
·
AMS direction--sensitive microphones
·
MaxBus
·
Last Mic Lock-On
·
NOMA
An
AMS direction--sensitive microphone
will activate only
for sounds which originate within a 120
_
acceptance angle in
front of the microphone. Other sounds outside of the 120
_
ac-
ceptance angle, including speech, background noise, and re-
verberation, will not gate the microphone on, regardless of lev-
el.
MaxBus
eliminates the poor audio quality that results
when a talker is picked up by more than one microphone. It
does this by controlling the number of microphones that may
activate for a single sound source. With MaxBus, one talker
will activate only one AMS8100 channel, even if multiple mi-
crophones are “hearing” that talker. However, Maxbus allows
multiple channels to activate simultaneously for multiple talk-
ers. See the illustrations below. The illustration on the left
shows how an AMS4000 or AMS8000 gates microphones for
two talkers — by automatically gating on any microphones that
pick up a talker within the 120
_
acceptance angle. The illustra-
tion on the right shows how MaxBus operates in the AMS8100
—even though the talkers are within the acceptance angle of
several microphones, only one microphone will activate for
each talker.
Last Mic Lock-On
maintains a seamless audio mix by
keeping the most recently activated microphone open until a
newly activated microphone takes its place. Without Last Mic
Lock-On, a long pause in conversation will cause all micro-
phones to turn off, and it may sound as if the audio signal has
been lost. Last Mic Lock-On ensures that background ambi-
ance will always be present. (This feature can be defeated via
DIP switch on the rear panel.)
NOMA
(Number of Open Microphones Attenuator) auto-
matically reduces the gain of the mixer as additional micro-
phones are activated. In a sound reinforcement application, if
the system gain is set below the feedback point with a single
microphone gated on, the increase in system gain with addi-
tional “on” microphones could cause feedback. NOMA pre-
vents this by automatically reducing all “on” microphone gains
by 3 dB as additional microphones are gated on. This main-
tains constant total system gain, avoiding feedback and per-
mitting the maximum microphone gains at all times. Also, this
consistency of system gain means that pickup of room noise
and reverberation also remains constant at the level of a single
microphone. (Note: NOMA is not the same as an automatic
gain control [AGC] and does not adjust input levels based on
loud or soft talking.)
Multiple miking situations—with several talkersparticipat-
ing—have always presented problems for the audio techni-
cian. If too few mics are used, the coverage of each talker may
vary, with one talker (nearest the mic) being louder and clearer
than the next. Talkers
farthest
from the mics will sound
“echoey” and reverberant, as very little of their direct sound
reaches the microphones. If too many mics are used, there’s
more background noise and reverberation pickup, as well as
less gain before feedback with a sound reinforcement (PA)
system.
It’s similar to having multiple video cameras all focused on
the same subject. If these camera signals are combined, the
result is a blurred image. When multiple microphones are open
for a single talker, the result is a blurred audio signal. It’s often
not practical for someone to turn mics on when they are need-
ed and off when they are not. The AMS8100 automatic micro-
phone mixer solves these problems.
The AMS8100 automatically attenuates (turns down) any
microphone not being used, greatly reducing the excess re-
verberation and feedback problems associated with the use of
conventional multiple microphone and mixer techniques.
When a new talker starts to speak, the AMS8100 immediately
selects and silently activates the most appropriate micro-
phone within 4 milliseconds.
Directional IntelliMix
signal proc-
essing enables the AMS8100 to provide clear, natural voice
pickup. The AMS8100 significantly reduces the problems of
“hollow” or “muddy” sound, and insufficient gain before feed-
back.
WITHOUT MaxBus
(AMS8000)
WITH MaxBus
(AMS8100)
*Shaded areas indicate
microphones gating on.
