General Technical Description; Wideband Design; Digital Hybrid Wireless ® Technology; No Pre-Emphasis/De-Emphasis - Lectrosonics HMa Instruction Manual

HMa

General Technical Description

Wideband Design

The HMa transmitter uses ±75 kHz wide deviation for
an excellent signal to noise ratio and wide dynamic
range. The DSP controlled input limiter features a wide
range dual envelope design which cleanly limits input
signal peaks over 30 dB above full modulation. Switch-
ing power supplies to provide constant voltages to the
transmitter circuits from the beginning (3 Volts) to the
end (1.7 Volts) of battery life, and an ultra low noise
input amplifier for quiet operation.
Digital Hybrid Wireless
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 (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.
Lectrosonics Digital Hybrid Wireless
come 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 that can be accomplished
only in the digital domain, even though the inputs and
outputs are analog.
Channel noise still impacts received signal quality and
will eventually overwhelm a receiver. Digital Hybrid
Wireless ® simply encodes the signal to use a noisy
Bias Voltage
42V,15V, 5V
Phantom
Power
Input
Amp
Digital
Pot
Shunt
Limiter
LCD
AUDIO
FREQ
UP
DWN
Bicolor
Modulation
LEDs
4
Technology
®
systems over-
®
+4V
A-D
Hi.Lo
Audio
Converter
Pass
Filter
11001001
Audio
Level
Digital Signal Processor
Microprocessor
channel as efficiently and robustly as possible, yield-
ing audio performance that rivals that of wholly digital
systems, without the power 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 resistance to interference.
However, unlike conventional FM systems, it does
away with the analog compandor and its artifacts.

No Pre-Emphasis/De-Emphasis

The Digital Hybrid Wireless
noise ratio high enough to preclude the need for con-
ventional pre-emphasis (HF boost) in the transmitter and
de-emphasis (HF roll-off) in the receiver. This eliminates
the potential for extreme distortion on 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 or 70 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 level sound
systems, can even cause damage to loudspeaker
systems. The roll-off is normally adjusted by ear while
listening as the system is operating.
D-A
Encoded Audio
Converter
and Pilot Tone
11001001
3 V
Battery
Reference
Crystal
Phase Locked Loop
Reference
Crystal
design results in a signal-to-
®
Filter
Amp
1.2V
4V
Switching
Power
Supply
-3.3V
+3.3V
Voltage
Final
Controlled
Amplifier
Oscillator
LECTROSONICS, INC.