Lectrosonics SM - Manual (Page 4)

SM
General Technical Description
Introduction
The SM transmitter uses ±75 kHz wide deviation for an
extremely high signal to noise ratio, switching power
supplies to provide constant voltages to the transmitter
circuits from the beginning (1.5 Volts) to the end (0.85
Volts) of battery life, and an ultra low noise input amplifier
for quiet operation. It is gain protected with a wide range
dual envelope input limiter which cleanly limits input
signal peaks over 30 dB above full modulation.
Servo Input
The SM input is a radically different input system com­
pared to previous Lectrosonics transmitter microphone
inputs. It is so superior that this input system will even­
tually be utilized by all Lectrosonics UHF transmitters.
This may cause some confusion but the advantages are
very real. The improvements are audible and make the
transmitters easier to use and much harder to overload.
It is no longer necessary on some mics to introduce
pads to prevent overload of the input stage, divide the
bias voltage down for some low voltage mics, or reduce
the limiter range at minimum gain settings.
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.
*US Patent Pending
Lectrosonics Digital Hybrid Wireless™ systems over­
come 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
tion via an analog FM wireless link. This proprietary
algorithm is not a digital implementation of an analog
compandor but a technique that can be accomplished
only in the digital domain, even though the inputs and
outputs are analog.
Channel noise still impacts received signal quality and
will eventually overwhelm a receiver. Digital Hybrid
Wireless™ simply encodes the signal to use a noisy
channel as efficiently and robustly as possible, yield­
ing audio performance that rivals that of wholly digital
systems, without the power and bandwidth problems
inherent in digital transmission.
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, it does away with the
analog compandor and its artifacts.
No Pre-Emphasis/De-Emphasis
The Digital Hybrid Wireless™ design results in a signal-
to-noise ratio high enough to preclude the need for
conventional pre-emphasis (HF boost) in the transmitter
and de-emphasis (HF roll off) in the receiver.
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
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