General Technical Description; General; Digital Hybrid Wireless Technology; No Pre-Emphasis/De-Emphasis - Lectrosonics SM Operating Instructions Manual

SM

GENERAL

The 400 system uses ±75 kHz wide deviation for an
extremely high signal to noise ratio. 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, and an ultra low noise op amp is
used as the input amplifier for quiet operation. It is gain
protected with a wide range dual envelope input limiter
which cleanly limits input signal peaks over 30 dB above
full modulation.
The terms 400 Series and Digital Hybrid Wireless™ describe the
same product line and are interchangeable.
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 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 and resistance to interference.
Lectrosonics Digital Hybrid Wireless™ systems over-
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 information via
an analog FM wireless link. This proprietary algorithm is
not a digital implementation of an analog compandor but
Bias
Voltage
0, 2 or 4 Volts
Servo Bias
Supply
Mic
Jack
1
2
Input
3
Amp
4
5
Digital
Pot
Audio
Level
Shunt
Limiter
LCD
Audio
Switch
Freq
Switch
Up/Down
Switches
Bicolor
Power
LED
Bicolor
Modulation
LEDs
4

GENERAL TECHNICAL DESCRIPTION

Note
™
+6v
A-D
Hi/Lo
Audio
Converter
Pass
Filter
11001001
Digital Signal Processor
Microprocessor
Phase Locked Loop
Reference
Crystal
Professional Audio Products Since 1971
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
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.
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. How-
ever, unlike conventional FM systems, it does away with
the analog compandor and its artifacts.

NO PRE-EMPHASIS/DE-EMPHASIS

The Digital Hybrid Wireless™ 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.
LOW FREQUENCY ROLL-OFF
A 12 dB per octave low frequency roll-off is provided in
the audio section, with the -3 dB point at 70 Hz. The
actual roll-off frequency will vary somewhat according to
the low frequency response of the mic capsule being
used.
The low frequency roll-off is used to remove subsonic (or
very low frequency) audio, often produced by air condi-
tioning systems, automobile traffic and other sources
Encoded
D-A
Audio and
Converter
Pilot Tone
11001001
Switching
Power
Supply
1.5V
Battery
SM
Block Diagram
+3.3v
+1.8v
+6v
-3v
Final
Voltage
50
Controlled Amplifier
Ohms
Oscillator
*US Patent Pending
Isolator