Lectrosonics MM400 - Manual User Manual download pdf (Page 4)

MM400

GENERAL TECHNICAL DESCRIPTION

If the unit will be used in a wet environment (possible immersion, perspiration, rain scenes, etc.) – be certain all

connectors have intact gaskets and that a properly sealed Lectrosonics waterproof mic connector is installed and

used with the microphone.

GENERAL

The 400 system uses 75kHz wide deviation for an extremely high signal to noise ratio. The switching power supplies

provide constant voltages to the transmitter circuits from the beginning (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 30dB above full modulation.

DIGITAL HYBRID 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 information in digital form, at the cost of some combination of power, bandwidth and resistance

to interference.

The Lectrosonics Digital Hybrid system overcomes 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 information 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. (As of

this writing, the patent is still pending, so we cannot reveal detailed information about the algorithm at this time.)

Channel noise still has an impact on received signal quality and will eventually overwhelm the receiver. The Digital

Hybrid simply encodes the signal to use a noisy channel as efficiently and robustly as possible, yielding audio

performance that rivals that of wholly digital systems, without the power and bandwidth problems inherent in digital

transmission. As always, these advantages come at a cost. The Digital Hybrid system requires fairly intensive digital

processing in both the transmitter and the receiver. These processors cost money, take up space and consume

power. The Digital Hybrid system also requires that the underlying RF link be of excellent quality, with better fre-

quency response and distortion characteristics than that required by conventional systems.

Because it uses an analog FM link, the Digital Hybrid enjoys all the benefits of conventional FM wireless 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.

+6V Bias

<--See Input Jack Wiring for details.

Transmitter

Phase Locked Loop

Voltage

Controlled

Oscillator

Freq

Switches

(Fits Switchcraft

plug #850.)

11001001

A-D

Converter

Digital Signal Processor

11001001

D-A

Converter

Shunt

Limiter

Bicolor

Modulation

LEDs

Microprocessor

1.5V

Lithium

Switching

Power

Supply

+3.3v

+3v

+1.8v

+6v

-3v

Isolator

Hi/Lo

Pass

Filter

Audio

Encoded

Audio +

Pilot Tone

4MHz

Reference

Bicolor

Power

LED

Mic

Jack

Supply

Audio

Level

Input

Amp

MM400 Block Diagram

LECTROSONICS, INC.

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