Crown FMX30 Manuel d'utilisateur télécharger pdf (Page 44)

Rev. 1.0

FMX30/FMX100/FMX250 User’s Manual

4—4

The RC networks in the processor use three different time constants to cover a

variety of signal conditions. Short, transient audio peaks produce quick gain

reduction with quick recovery, while long term level trends produce slower gain

reduction, with slow recovery. Highband processing shifts the pre-emphasis curve

rather than affecting overall gain. The amount of short-term expansion and gain

reduction is adjusted by control R650, located on the front panel display board.

You may select from three pre-emphasis curve, 75 µsec, 50 µsec, 25 µsec, or Flat, by

jumpering the appropriate pins on header JP1. Controls R29 and R65 are for making

fine adjustments to the pre-emphasis curve.

The stereo generator board (Illustration 4-3) generates a composite stereo signal

from left and right-channel audio inputs. The Stereo Generator board also performs

the following additional functions:

• Low-pass filtering for the audio processor

• Stereo generation

• SCA input

• Audio de-emphasis for the processed audio output.

4.3.1 Low-pass filter

The output of the buffer amplifier on the Audio Processor board drives the input a

low-pass filter. This eighth-order, elliptical, switched-capacitor filter is located on

the Stereo Generator board to take advantage of the Stereo Generator’s ground

plane and close proximity to the 1.52 MHz clock. The output of the filter returns to

the Audio Processor board.

Illustration 4-3 Stereo Generator Board

Stereo

Generator

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Crown FMX30 Manuel d'utilisateur Page 44