Crown FMX30 Manuel d'utilisateur télécharger pdf (Page 43)

Rev. 1.0

Principles of Operation 4—3

The audio processor board (Illustration 4-2) performs five functions:

• Balanced input amplifier

• Gain selection

• Low-pass filter

• Signal compression, limiting and expansion

• Pre-emphasis

Each of these functions are discussed in the following section.

4.2.1 Balanced Input

Audio input from the rear-panel, XLR connectors route to differential-input

amplifiers and then to a buffer amplifiers. The front panel gain switch sets one of

four gain levels at the output of the buffer amplifiers. The output of the buffer

amplifiers drive both the front panel indicators and a low-pass filter stage on the

Stereo Generator board.

4.2.2 Audio Processor

The audio processor section provides the following audio control functions:

• Compressor

• Limiter

• Expander

The audio signal is passed through a low-pass filter on the Stereo Generator board

(see Section 4.3.1). After the signal renenters the processor board an additional

third-order, low-pass filter attenuates products below 30 Hz. The audio processor

then takes the incoming audio—ranging in level from -20 to + 5 dBm—and

modulates the transmitter to a consistent, easily understood level, without

overmodulation.

Illustration 4-2 Audio Processor Board

Audio

Processor

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Crown FMX30 Manuel d'utilisateur Page 43