MACKIE HDR24/96 - Manual (Page 207)

HDR 24/96
Appendix H – Gozintas and Gozoutas Appendix H – Gozintas and Gozoutas
207
Mackie offers four different I/O interface cards designed for different applications. It is not necessary to
use the same type of card in all three of the audio I/O slots – you can mix cards in the same machine for
connecting channels to different types of equipment.
Your deck of cards includes:
AIO-8 – Analog
OPT-8 – Digital, ADAT Optical format
DIO-8 – Digital, combined ADAT Optical and TDIF
PDI-8 – Digital, AES/EBU format
There are a few rules, however, which you must understand when choosing or installing I/O cards:
• The relationship between I/O slots and recorder tracks is fixed. You can’t install one analog I/O card
in a single slot and route an input connected to that card to any recorder track.
• With the exception of the DIO-8 ADAT/TDIF I/O card, the inputs and outputs are the same format.
You can’t connect mic preamps directly to the recorder through an analog input card and
simultaneously connect the recorder’s outputs digitally to a digital console for monitoring while
tracking.
• When operating in the double clock speed mode (88.2 or 96 kHz sample rates), each I/O slot provides
only four channels rather than eight, and tracks 13-24 go away.
AIO-8 Analog I/O
The AIO-8 provides 8 channels of analog input and output. The card has two female 25-pin D-
Subminiature connectors, one for inputs, and the other for outputs.
Inputs and Outputs
Inputs are balanced with nominal input sensitivity of +4 dBu. This means that with a steady state
(sine wave) input signal of +4 dBu, expect the front panel record level meters to illuminate the
LED between –15 and –20 dB. At this level, the GUI meters indicate –20 dB. The difference is
due to the lower resolution of the LED meters. For a nominal –10 dBV output, expect the LED
meters to indicate between –25 and –30 dB, and the GUI meters to indicate –30 dB.
The AIO-8 card is not suitable for direct connection of an instrument pickup, but may work fine
for connecting an electronic keyboard.
The card is calibrated for unity gain, so the output level will be the same as the input level.
The outputs are single-ended, impedance balanced. This means that they provide good rejection
of common mode noise (typically, hum and RF interference picked up in the cables) when
connected to balanced inputs. An added bonus is that they can be connected to unbalanced inputs
without affecting the output level or risking damage to the output circuitry.
There are certain input circuit designs (we call them bad designs be we don’t use them on our
equipment) which are balanced, and which require a differential source (which the AIO-8 card
isn’t) in order to get full gain and full headroom. We don’t see this on new equipment, but if you
have an older budget priced console, you might want to check this out before attempting to use
AIO-8 cards with it. A quick test is to see if the console performs normally with an unbalanced
source connected to its balanced inputs.
Technical Reference 207