Input Resolution Indicators; Output Formats; Ambus Cards; Abs, Paqrat & Ambus - Apogee AD-8000 Operating Manual

Four AMBus slots on the AD-8000 allow up to eight channels of digital input, in virtually any format. The on-
board microprocessor senses the identity of any AMBus card which is plugged in, and will enable the card to
be selected on the front panel as an input. It will also allow the card to receive the eight digital output channels
(if permitted by the specific card).

Input Resolution Indicators

Beneath the Source Selection LEDs are three lights that indicate the digital word length of the selected dig-
ital input – 16, 20 or 24 bits. If the selected signal does not include status bits indicating the word length, the
AD-8000 wwill measure the actual word length of the selected digital input.
Digital Outputs
AES/EBU and S/PDIF
The eight output channels go directly to the four AES/EBU XLR jacks on the back. In addition, the channel
pair that is being monitored, as determined by the headphone selection switch, is routed to the S/PDIF output
connector.

AMBus Cards

If an AMBus card contains one or more output channels, then the digital outputs that are sent out on the
AES/EBU connections will be sent out on the AMBus card outputs as well. For example, if an ADAT card is
plugged in, the ADAT output connector will carry the same audio that is going out on AES/EBU jacks 1-4.
ABS, PaqRat and AMBus
Some AMBus cards, such as those for ADAT, TDIF and AES/EBU, have built-in ABS (Apogee Bit-Splitting)
for recording six channels at 20-bit resolution ("6/20"), or four channels at 24-bit resolution ("4/24", compati-
ble with Rane Corporation's PaqRat
Operation of the ABS or PaqRat 4/24 mode is straightforward. A stereo digital audio signal, with up to 24-
bit resolution, is input to an AMBus card with the ABS/PaqRat capability. This stereo signal is divided into four,
and recorded to four tracks of the destination machine. The AMBus slot into which the card is placed deter-
mines whether AD-8000 channels 1-4 or 5-8 are used. Up to four stereo pairs can be recorded simultaneously
with two AMBus cards. A card in Slot A takes AD-8000 channels 1-4 (which would typically be routed to machine
1) and a card in slot B or D take channels 5-8 (machine 2).
During playback, ABS in 4/24 mode accepts the four tracks from the tape transport (again, selectable for
tracks 1-4 or 5-8 by means of the card slot), and converts these four tracks back to the original high resolution
stereo signal. The track arrangement of the ABS 6/20 mode is more complex, but the principle is similar. A full
description of how to select the ABS bit-splitting mode you require, and how to use the card's bit-splitting fea-
tures, is provided in the card's documentation.

Headphone Monitor

Any channel pair that is going out via the AES/EBU output jacks can also be routed to the headphone jack
on the front panel using the MONITOR selector switch. When the source monitor mode (the default) is select-
ed, the monitored output reflects any processing that is being carried out, such as DC removal, UV22, or mut-
ing. When monitoring an external signal via an AMBus card, the monitored output is unprocessed. Similarly, the
monitored output channel pair can be from either a digital or analog source, depending on the front panel set-
tings. The seven-segment indicator in the MONITOR section indicates relative headphone volume (0–9), with
the toggle switch controlling volume up or down.
Stereo D/A (Optional)
The 24-bit stereo D/A card available for the AD-8000 contains a 24-bit DAC with filtering, digital de-empha-
sis (including de-emphasis override for digital signals with an incorrectly-set emphasis flag), DC removal, auto-
matic soft mute and gain adjustment circuitry. The channel pair that is routed to the D/A card is the same chan-
nel pair being routed to the front panel headphone jack.
AD-8000 Operating Manual

Output Formats

® ) on eight 16-bit digital multitrack tape tracks.

Analog Outputs

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