Redbox User Handbook No 1
1
DIGIT
AL A
UDIO C
ONVERTERS - RB
-ADD
A
DIGITAL AUDIO CONVERTERS
1 RB-ADDA Combined A/D and D/A Converter
Introduction
Fig 1-1: RB-ADDA Front Panel
Using 24 bit, 96kHz capable devices, the RB-ADDA A/D and D/A Converter is a 1U rack-
mount which produces an AES/EBU or S/PDIF level digital audio output from a balanced XLR
or unbalanced phono stereo audio input. The unit also produces a stereo balanced XLR or
unbalanced phono output from an incoming AES/EBU or S/PDIF digital input signal.
The unit operates in four modes:
Master Mode
- In this mode the unit receives an analogue audio signal, which
is digitised and formatted for digital serial transmission (IEC958). The necessary
clock signals are generated internally from an on board master clock at a
selectable rate (32kHz, 44.1kHz, 48kHz, 64kHz, 88.1kHz or 96kHz).
Slave Mode
- In this mode the unit automatically detects the presence of a digital audio
sync signal, if present at the digital input, and synchronises the digital output to it. If no sync
is present, no output will be generated.
Auto Mode
- Here the unit synchronises to the digital audio sync signal if present at the
digital input and uses the internal master clock only if no sync input signal is detected. In
this case, the internal master clock is used at the selected sample rate.
Auto Lock Mode
- This operates like the auto mode. The difference is that if the sync input
signal is lost, the unit will revert to an internal master clock rate as near as possible to the
last sync signal received.
When operating in sync modes, the front panel power LED flashes whenever the unit is not
synchronised to the incoming digital signal, or when the unit is being calibrated. The RB-
ADDA should be calibrated once it has been powered up for more than 10 minutes.
The analogue inputs have left and right level controls using pre-set potentiometers and
DIP switches allowing a signal range from +9dBu to +27dBu. The analogue outputs have
an output level control, allowing full-scale settings selectable from +12dBu, +18dBu or
+24dBu. There are factory-set internal level controls for the analogue outputs allowing gain
adjustment of ±1dB.
There are buttons to select either the AES/EBU or S/PDIF input or output for the D/A and
A/D sections respectively. The output bit depth can be selected from 16, 20 or 24 bits.
Inputs of a different bit depth to the output are dithered using a psychoacoustic noise filter.
1
