Lectrosonics Inc SMWBB2 ユーザーズマニュアル

5

Introduction

The design of the SMWB transmitter delivers the ad-

vanced technology and features of Digital Hybrid Wire-

less

®

 in a Lectrosonics belt-pack transmitter at a modest 

cost. Digital Hybrid Wireless

®

 combines a 24-bit digital 

audio chain with an analog FM radio link to eliminate a 

compandor and its artifacts, yet preserve the extended 

operating range and noise rejection of the finest ana-

log wireless systems. DSP “compatibility modes” allow 

the transmitter to also be used with a variety of analog 

receivers by emulating the compandors found in earlier 

Lectrosonics analog wireless and IFB receivers, and 

certain receivers from other manufacturers (contact the 

factory for details).
The housing is a rugged, machined aluminum package. 

The input jack is a standard Lectrosonics 5-pin type for 

use with electret lavaliere mics, dynamic mics, musi-

cal instrument pickups and line level signals. The LEDs 

on the keypad allow quick and accurate level settings 

without having to view the receiver. The unit is powered 

by two AA batteries. The antenna port uses a standard 

50 ohm SMA connector.
The switching power supplies in the provide constant 

voltages to the transmitter circuits from the beginning to 

the end of battery life, with output power remaining con-

stant over the life of the battery. The input amplifier uses 

an ultra low noise op amp. Input gain is adjustable over 

a 44 dB range, with a DSP-controlled dual envelope 

input limiter providing a clean 30 dB range to prevent 

overload from signal peaks.

About Digital Hybrid Wireless

®

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, operating range 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-

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.
Since the RF link between transmitter and receiver is 

FM, channel noise will increase gradually with in-

creased operating range and weak signal conditions, 

however, the Digital Hybrid Wireles system handles this 

situation elegantly with rarely audible audio artifacts as 

the receiver approaches its squelch threshold.

In contrast, a purely digital system tends to drop the 

audio suddenly during brief dropouts and weak signal 

conditions. The Digital Hybrid Wireless

 

system simply 

encodes the signal to use a noisy channel as efficiently 

and robustly as possible, yielding audio performance 

that rivals that of purely digital systems, without the 

power, noise and bandwidth problems inherent in digital 

transmission. Because it uses an analog FM link, Digital 

Hybrid Wireless

 

enjoys all the benefits of conventional 

FM wireless systems, such as excellent range, efficient 

use of RF spectrum, and long battery life.

Servo Bias Input and Wiring

The input preamp is a unique design that delivers 

audible improvements over conventional transmitter 

inputs. Two different microphone wiring schemes are 

available to simplify and standardize the configuration. 

Simplified 2-wire and 3-wire configurations provide sev-

eral arrangements designed for use only with servo bias 

inputs to take full advantage of the preamp circuitry.
A line level input wiring provides an extended frequency 

response with an LF roll-off at 35 Hz for use with instru-

ments and line level signal sources.

DSP-controlled Input Limiter

The transmitter employs a digitally-controlled analog 

audio limiter prior to the analog-to-digital converter. 

The limiter has a range greater than 30 dB for excellent 

overload protection. A dual release envelope makes the 

limiter acoustically transparent while maintaining low 

distortion. It can be thought of as two limiters in series, 

connected as a fast attack and release limiter followed 

by a slow attack and release limiter. The limiter recovers 

quickly from brief transients, so that its action is hidden 

from the listener, but recovers slowly from sustained 

high levels to keep audio distortion low and preserve 

short term dynamic changes in the audio.

Recorder function

The SMWB has a built in recording function for use in 

situations where RF may not be possible or to work as 

a stand alone recorder.  The record function and trans-

mit functions are exclusive of each other - you cannot 

record AND transmit at the same time.  The recorder 

samples at 44.1kHz rate with a 24 bit sample depth. 

(the rate was selected due to the required 44.1kHz rate 

used for the digital hybrid algorithm). The micro SD card 

also offers easy firmware update capabilities without 

the need for a USB cable or driver issues.