Lectrosonics SMV - Manual (Page 4)

SMV Series
LECTROSONICS, INC. 4
Variable 1.8 - 4v
+6V
+5V 5V
Regulator
Servo Bias Input
The voltage and current requirements of the wide vari-
ety of electret microphones used in professional appli-
cations has caused confusion and compromises in the
wiring needed for wireless transmitters. To address this
problem, the unique Servo Bias input circuit provides an
automatically regulated voltage over a very wide range
of current for compatibility with all microphones.
Digital Hybrid Wireless ® Technology
All wireless links suffer from channel noise to some de-
gree, and all wireless microphone systems seek to mini-
mize the impact of that noise on the desired signal. Con-
ventional analog systems use compandors for enhanced
dynamic range, at the cost of subtle artifacts (typically
“pumping” and “breathing”). Wholly digital systems defeat
the noise by sending the audio information in digital form,
at the cost of some combination of power, bandwidth and
resistance to interference.
Digital Hybrid systems overcome channel noise in a
dramatically new way, digitally encoding the audio in the
transmitter and decoding it in the receiver, yet still send-
ing the encoded information via an analog FM wireless
link. This proprietary algorithm is not a digital imple-
mentation of an analog compandor but a technique that
can be accomplished only in the digital domain, even
though the inputs and outputs are analog.
Because it uses an analog FM link, the Digital Hybrid
system enjoys all the benefits of conventional FM wire-
less systems and it does away with the analog compan-
dor and its artifacts.
General Technical Description
No Pre-Emphasis/De-Emphasis
The Digital Hybrid 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. This eliminates the potential
for distortion of signals with abundant high-frequency
information.
Low Frequency Roll-Off
The low frequency roll-off can be set for a 3 dB down
point at 35, 50, 70, 100, 120 and 150 Hz to control sub-
sonic and very low frequency audio content in the au-
dio. The actual roll-off frequency will vary slightly depend-
ing upon the low frequency response of the microphone.
Excessive low frequency content can drive the transmit-
ter into limiting, or in the case of high level sound sys-
tems, can even cause damage to loudspeaker systems.
The roll-off is normally adjusted by ear while listening
as the system is operating.
Input Limiter
A DSP-controlled analog audio limiter is employed be-
fore the A-D converter. The limiter has a range of more
than 30 dB for excellent overload protection. A dual re-
lease envelope makes the limiter acoustically transpar-
ent while maintaining low distortion. It can be thought of
as two limiters in series, a fast attack and release limiter
followed by a slow attack and release limiter. The limiter
recovers quickly from brief transients, with no audible
side effects, and also recovers slowly from sustained
high levels to keep audio distortion low while preserving
short term dynamics.