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

LECTROSONICS, INC.

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

degree, and all wireless microphone systems seek to

minimize the impact of that noise on the desired sig-

nal. Conventional analog systems use compandors for

enhanced dynamic range, at the cost of subtle artifacts

(typically “pumping” and “breathing”). Wholly digital sys-

tems 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

sending the encoded information via an analog FM

wireless link. This proprietary algorithm is not a digital

implementation of an analog compandor but a tech-

nique that can be accomplished only in the digital do-

main, 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 com-

pandor 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

subsonic and very low frequency audio content in

the audio. The actual roll-off frequency will vary slightly

depending upon the low frequency response of the

microphone.

Excessive low frequency content can drive the trans-

mitter into limiting, or in the case of high output sound

systems, it 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.

Variable 1.8 - 4v

+6V

+5V

Regulator

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