User's Manual

Wideband Digital Hybrid
®
Plug-On Transmitter
Rio Rancho, NM
5
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 level sound
systems, 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
before the analog-to-digital (A-D) converter. The limiter
has a range of more than 30 dB for excellent overload
protection. A dual release envelope makes the limiter
acoustically transparent while maintaining low distor-
tion. 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 and while preserving short term
dynamics.
Signal Encoding and Pilot Tone
In addition to controlling the limiter, the DSP also
encodes the digitized audio from the A-D converter
and adds an ultrasonic pilot tone to control the re-
ceiver’s squelch. A pilot tone squelch system provides
a reliable method of keeping a receiver output muted
(squelched) even in the presence of significant inter-
ference. When the system is operating in the hybrid
mode, a different pilot tone frequency is generated
for each carrier frequency in 100 kHz increments to
prevent inadvertent squelch problems and simplify
multi-channel coordination.
Microprocessor and DSP
A microprocessor monitors user command inputs from
the control panel buttons and numerous other internal
signals. It works intimately with the DSP to ensure the
audio is encoded according to the selected Compatibil-
ity Mode and that the correct pilot tone is added to the
encoded signal.
Compatibility Modes
The transmitter was designed to operate with Lectro-
sonics Digital Hybrid Wireless
®
receivers and will yield
the best performance when doing so. However, due to
the flexibility of digital signal processing, the transmit-
ters can also operate in various compatibility modes
(vary per specific model) for use with Lectrosonics
Mode 3 and IFB receivers. It will also work with certain
non-Lectrosonics receivers. Contact your sales repre-
sentative or the factory for a complete list of compat-
ible non-Lectrosonics receivers.
Control Panel
The control panel includes four membrane switches and
an LCD screen to adjust the operational settings. Multi-
color LEDs are used to indicate audio signal levels for
accurate gain adjustment and for battery status.