Lectrosonics UCR411 - Manual (Page 4)

SMART SQUELCH TM
The UCR411 employs a sophisticated squelching system
in an attempt to deliver the cleanest possible audio during
marginal conditions of reception. Any squelching system
faces inevitable trade-offs: squelch too much and valu­
able audio information may be lost, squelch too little and
excessive noise may be heard; respond too rapidly and
the audio sounds “choppy,” respond too sluggishly and
syllables or entire words can be cut off.
The UCR411 combines several techniques to achieve an
optimal balance, removing distracting noise, without the
squelching action itself becoming a distraction. One of
these techniques involves waiting for a word or syllable
to complete before squelching. Another incorporates
recent squelching history and recent signal strength,
adjusting squelching behavior dynamically for the most
serviceable result under variable conditions. Using these
and other techniques, the UCR411 can deliver accept­
able audio quality from otherwise unusable signals.
In the PILOT TONE BYPASS mode, the squelch system
is disabled. Received audio remains unmuted at all
times with this setting.
SMART NOISE REDUCTION (SmartNR TM )
The UCR411 has been meticulously designed using the
best available low noise components and techniques.
Nonetheless, the wide dynamic range of digital hybrid
technology, combined with flat response to 20 kHz,
makes it possible to hear the -120 dBV noise floor in the
mic preamp, or the (usually) greater noise from the
microphone itself. (To put this in perspective, the noise
generated by the recommended 4k Ohm bias resistor of
many electret lavaliere mics is –119 dBV and the noise
level of the microphone’s electronics is much higher.) In
order to reduce this noise and thus increase the effective
dynamic range of the system, the UCR411 is equipped
with a Smart Noise Reduction algorithm, which removes
hiss without sacrificing high frequency response.
The Smart Noise Reduction algorithm works by attenuat­
ing only those portions of the audio signal that fit a
statistical profile for randomness or “electronic hiss”.
Because it isn’t simply a sophisticated variable low pass
filter as in Lectrosonics’s 195 and 200 series designs,
much greater transparency is thus obtained. Desired
high frequency signals having some coherence such as
speech sibilance and tones are not affected.
The Smart Noise Reduction algorithm has three modes,
selectable from a user setup screen. When switched
OFF, no noise reduction is performed and complete
transparency is preserved. All signals presented to the
transmitter’s analog front end, including any faint micro­
phone hiss, will be faithfully reproduced at the receiver.
When switched to NORMAL, the factory default setting,
enough noise reduction is applied to remove most of the
hiss from the mic preamp and some of the hiss from
lavaliere microphones. The noise reduction benefit is
dramatic in this position, yet the degree of transparency
maintained is exceptional. When switched to FULL,
enough noise reduction is applied to remove most of the
hiss from nearly any signal source of reasonable quality,
assuming levels are set properly at the transmitter. This
additional noise reduction comes at the cost of some
transparency for low-level room noise, yet the algorithm
remains undetectable under most circumstances.
UCR411 Block Diagram
50
50
2K
2K
uP
LCD
Display
Panel
PILOT TONE
DETECTOR
FILTER FILTER
uP uP
DIGITAL SIGNAL
PROCESSOR
Attenuation
CERAMIC
FILTER
2ND
MIXER
10.7 MHZ
SAW
FILTER
244 MHz
IF AMP
AMP
XLR
OUT
HI-LEVEL
MIXER
RF MODULE
3RD MIXER
AND
IF AMP
50KHz
LP FILTER
XTAL
CONTROLLED
3rd
OSCILLATOR
SAW
FILTER
244 MHz
IF AMP
COUNTING
DETECTOR
AUDIO
AMP
ANTENNA
COMBINING
FILTER
E PROM 2
1st
VCO
Smart Diversity
PLL
SYNTHESIZER
LC
Filter
Output
Level
Adjust
Digital
Attenuator
2nd
VCO
FILTER
2 (HI)
1 (COMMON)
3 (LO)
4