User guide
Workstation Card Rev 1.2 Operation
Genex Research Limited Page 7
Systems with Multiple Interfaces
In a system where more than one interface is used all interfaces must be sample locked. The primary
interface (card 1, slot A) in a system should always be the clock master (unless an external sync de-
vice is being used - see later).
Where available, word clock should be used to synchronise interfaces. This is on the back of the
GXA8/D8, not the GX8-WSIF card. This clock is not internally terminated so converters can be daisy-
chained together with BNC T-pieces. This avoids cascading PLL stages, which would introduce jitter.
A 75Ω terminator should be fitted to the T-piece at the last converter. Use the front panel CLOCK
SOURCE button to select word clock (note the converter must be fitted with firmware v3.0 for this to
work).
Interfaces like the Digidesign 888/24 I/O that do not use word clock should be locked via 256x Fs
clock connections on the back of the GX8-WSIF Workstation Card. This high-speed clock is compati-
ble with other 256x Fs clocks such as the Apogee Slave Clock and the Digidesign Super Clock. The
256x sample clock output from the primary interface should connect directly to the 256x clock input on
the next interface. The clock output from this interface should be connected to directly to the clock
input on the next interface, and so on.
The 256x sample clock input is internally terminated so external terminators must not be used, nor
should BNC T-pieces be employed.
NOTE: The standard Genex system involving a GXA8, GXD8 and one Workstation Interface Card is
not considered a multiple interface system since both converters used together provide A/D and D/A
support for a single 50-pin interface connection.
Using External Synchronisation Devices
With the inclusion of 256x clock input and output BNCs, the Genex Workstation Card may be used in
a system synchronised from external synchronisation devices such as the MOTU DTP or the
Digidesign USD. These devices provide audio clocks from sources such as video and SMPTE time-
code, etc.
To lock the GXA8 / GXD8 to the 256x clock input on the Workstation Card, simply feed in a 256x
clock signal into the clock input on the workstation card. It is automatically detected and the converter
locks to it. (Note: if the converter has firmware earlier than v3.0 fitted, ensure that the sync source is
set to INTERNAL via the hardware setup control panel on the computer which normally puts the con-
verter into master mode).
In many applications, a digital audio editing system must lock to timecode striped onto an analogue
tape machine. Such a source of timecode is liable to exhibit jitter and speed fluctuations. The Genex
converters and Workstation card are one of the few third party workstation interfaces that will lock to
and track an audio clock coming from the MOTU DTP or Digidesign USD that have in turn been
locked to such a timecode source. How to achieve this is detailed below:
Locking to Variable Timecode
If your timecode source (via a MOTU DTP or Digidesign USD) is variable such as from ana-
logue tape or your system requires the use of Varispeed, the Genex GXA8 / GXD8 and
Workstation Card can be set to follow and stay locked to it.
Normally, the GXA8 / GXD8 would be the clock master in order to take advantage of the high
precision crystal source inside. Even if the converter is not the clock master then the Wide or
Precision lock modes take advantage of a variable high-precision crystal. However, in order to
provide support for the various modified video and film rates, the GXA8 and GXD8 are de-
signed with a wide lock PLL. This PLL can also be used to lock to a moving or varispeed
source. In order to configure the units this way the user must do the following:
• On the GXA8 / GXD8, press and hold the LOCK MODE button until both the ARROW UP and
ARROW DOWN indicators (next to the SAMPLE-RATE indicators) illuminate, then release. The
unit is now in “varispeed” mode. To release, press and hold again until the indicators go
out.
In the standard Genex setup with a GXA8, GXD8 and one Workstation Card, both of the con-
verters must be configured in this way. They will follow a varying clock via word clock, AES,
256x sample clock, or any other clock source.