Lectrosonics T4 User Manual download pdf (Page 5)

Multi-Frequency IFB Transmitter

Rio Rancho, NM

A user-selectable low frequency roll-off can be set for

35 Hz or 50 Hz. The recommended 50 Hz default set-

ting helps to remove wind and trafﬁc noise, air con-

ditioner rumble, and other sources of undesired low

frequency audio. The 35 Hz setting offers a fuller range

of sound in the absence of adverse conditions.

Input Limiter

A DSP-controlled analog audio limiter is employed

before the analog-to-digital converter. The limiter has a

range of more than 30 dB for excellent overload protec-

tion. A dual release envelope makes the limiter acousti-

cally transparent while maintaining low distortion. It can

be thought of as two limiters in series: a fast attack and

release limiter followed by a slower attack and release

limiter. The dual release limiter recovers quickly from

brief transients but recovers more slowly from sustained

high levels, keeping audio distortion low while preserv-

ing short term dynamic changes. When the audio

meter on the LCD display widens slightly as it reaches

zero, limiting is indicated. When the zero changes to a

letter C, severe limiting and/or clipping is indicated.

Audio DSP and Noise Reduction

Lectrosonics IFB systems use a single band compan-

dor and pre-emphasis for exceptional IFB audio quality.

The IFBT4 performs these traditionally analog functions

entirely in the digital domain, maintaining historical

compatibility while requiring fewer adjustments. When

the IFBT4 is conﬁgured for compatibility with other

types of wireless systems, such as the Lectrosonics

100, 200 and 400 Series and some other brands, the

DSP stops IFB companding and instead performs the

appropriate audio processing for the chosen mode.

While all of these modes have won acclaim for perform-

ing well in their respective spheres, the 400 Series

mode (Digital Hybrid Technology) offers objectively

superior audio performance and is recommended when

the receiver is capable of supporting it.

Pilot Tone Squelch System

Lectrosonics IFB systems use a special “pilot tone” so

that valid IFB signals can be distinguished from RF

interference. During normal operation, an IFB receiver

will listen for the distinctive pilot tone, remaining silent

(squelched) until the pilot tone is detected. The pilot

tone is located well above audio frequencies and is

never passed through to the receiver’s audio output.

The beneﬁt of the pilot tone squelch system is that the

receiver will remain muted until it receives the pilot tone

from the matching transmitter, even if a strong interfer-

ing RF signal is present on the carrier frequency of the

system.

When the IFBT4 is operated in compatibility modes

other than IFB, it generates pilot tones as appropriate

for the chosen mode.

Frequency Agility

The IFBT4 transmitter uses a synthesized, frequency

selectable main oscillator. The frequency is extremely

stable over a wide temperature range and over time.

The transmitter’s standard tuning range covers 256 fre-

quencies in 100 kHz steps over a 25.6 MHz band. This

ﬂexibility signiﬁcantly helps avoid interference problems

in mobile or traveling applications.

Power Delay

When powering the transmitter on and off, and when

switching between the XMIT and TUNE modes, intel-

ligent circuitry adds brief delays in order to allow time

for circuits to stabilize, both locally and in the matching

receiver. These delays prevent clicks, thumps or feed-

back from entering the sound system.

Microcontroller

The microcontroller oversees most system operations,

including RF frequency and output, DSP audio func-

tions, buttons and display, and more. User settings

are stored in non-volatile memory, so they are retained

even when the power is turned off.

Transmitter

The IFBT4 transmitter operates at a high RF power

level to ensure a clean signal free of dropouts and

noise. All transmitter circuits are buffered and ﬁltered

for excellent spectral purity. The IFBT4’s clean signal

reduces the chances for interference in multiple trans-

mitter installations.

Antenna System

The 50 Ohm BNC output connector will work with stan-

dard coaxial cabling and remote antennas.

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Lectrosonics T4 User Manual Page 5

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