HM/E01
LECTROSONICS, INC.
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Wideband Design
The HM transmitter uses ±50 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. Switching pow-
er supplies provide constant voltages to the transmitter
circuits from the beginning (3 Volts) to the end (1.7 Volts)
of battery life. An ultra low noise input amplifier provides
quiet operation.
Digital Hybrid Wireless
®
Technology
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
®
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 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.
General Technical Description
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, 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
®
design results in a signal-
to-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 suppress very low frequen-
cy audio content. 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.
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