6-10
TECHNICAL DATA Orban Model 8400
decimation to the 8400 system sample rate being done in the system DSP, as was done
for the analog input.
A second receiver/converter, IC502, accepts a second digital audio signal to enable the
8400’s output sample rate to be locked to a reference sample rate presented to J501.
These chips are surface-mounted and are not field-replaceable.
Output Circuits
This circuitry interfaces the DSP to the analog and digital audio outputs. The digital au-
dio from the DSP is transmitted to the digital-to-analog converter (D/A) and output sam-
ple rate converter (SRC). The digital-to-analog (D/A) converter converts the digital audio
words generated by the DSP to analog audio. High-speed D/A converters do the same for
the composite outputs, each of whose outputs is smoothed by a passive LC reconstruction
filter. The analog output stages scale and buffer the D/A output signal to drive the analog
output XLR connectors with a low impedance balanced output. The digital output trans-
mitter accepts the digital audio words from the output sample rate converter (SRC) and
transmits them in AES/EBU-format digital audio signals on the digital output connector.
1. Stereo Digital-to-Analog (D/A) Converter
Located on input/output board
The D/A, IC211, is a stereo, 24-bit delta-sigma converter. It receives the serial left and
right audio data samples from the DSP at 64 kHz sample rate, and converts them into au-
dio signals requiring further, relatively undemanding analog filtering. IC211 is surface-
mounted and is not field-replaceable.
2. Analog Output Stages
Located on input/output board
The left and right analog signals emerging from IC211 are each filtered, amplified, and
applied to a floating-balanced integrated line driver, which has a 50Ω output impedance.
The line driver outputs are applied to the RF-filtered left and right analog output connec-
tors. These analog signals can represent either the transmitter or monitor output of audio
processing.
Component-Level Description:
The left channel signal emerging from IC211 is filtered by IC201 and associated
components. The purpose of these stages is to reduce the out-of-band noise en-
ergy resulting from the delta-sigma D/A’s noise-shaping filter, and to translate the
differential output of the D/A converter into single-ended form. These compo-
nents apply a 3
rd
order low-pass filter to the differential signal from the D/A. This
filter does not induce significant overshoot of the processed audio, which would
otherwise waste modulation.
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