Lectrosonics MM400c - Manual (Page 6)

MM400C
LECTROSONICS, INC. 6
General
The 400 Series (or Digital Hybrid Wireless™) system
uses 75 kHz wide deviation for an extremely high signal
to noise ratio. The switching power supplies provide
constant voltages to the transmitter circuits from the be-
ginning (1.5 Volts) to the end (0.85 Volts) of battery life.
The input amplifier uses an ultra low noise op amp for
quiet operation. It is gain controlled with a wide range
dual envelope input compressor which cleanly limits
input signal peaks over 30 dB above full modulation.
Note: The terms 400 Series and Digital Hybrid
Wireless ™ describe the same product line and are
interchangeable.
Digital Hybrid Wireless ® Technology
All wireless links suffer from channel noise to some
degree, and all wireless microphone systems seek to
minimize the impact of that noise on the desired signal.
Conventional analog systems use compandors for
enhanced dynamic range, at the cost of subtle artifacts
known as “pumping” and “breathing”. Wholly digital
systems defeat the noise by sending the audio informa-
tion in digital form, at the cost of some combination of
power, bandwidth and resistance to interference.
The Lectrosonics Digital Hybrid Wireless
® system over-
comes channel noise in a dramatically new way, digitally
encoding the audio in the transmitter and decoding it
in the receiver, yet still sending the encoded informa-
General Technical Description
tion via an analog FM wireless link. This proprietary
algorithm is not a digital implementation of an analog
compandor but a technique which can be accomplished
only in the digital domain, even though the inputs and
outputs are analog signals.
Because it uses an analog FM link, Digital Hybrid Wire-
less ™ enjoys all the benefits of conventional FM wire-
less systems, such as excellent range, efficient use of
RF spectrum, and resistance to interference. However,
unlike conventional FM systems, the Digital Hybrid has
done away with the analog compandor and its artifacts.
Low Frequency Roll-Off
A 12 dB per octave low frequency roll-off is provided in
the audio section, with the -3 dB point at 70 Hz. The
actual roll-off frequency will vary somewhat according
to the low frequency response of the mic capsule being
used.
The low frequency roll-off is used to remove subsonic
(or very low frequency) audio, such as that produced
by air conditioning systems or automobile traffic from
the audio signal. Excessive low frequency content in
the audio input can cause a variety of audio problems
including driving the transmitter into limiting. In sound
reinforcement systems, as another instance, excessive
low frequency content can cause excessive power am-
plifier drain or even damage to loudspeaker systems.
+5V Bias
11.3 MHz