SAM64 User Manual v1.6
12
GPIO Control
As the SAM64 could be installed in a central control
room or outside broadcast vehicle using automated
system software applications, external control of
the SRCs can be achieved via the GPIO port. Simple
contact closure (grounding the GPI) enables any or
all the SRCs, allowing them to be switched in or
out from a remote point. Maximum recommended
operating distance is 5 m (though this may be
increased by the use of external relays or similar).
Refer to the pinout on page 10 for wiring details.
Synchronisation
The SAM64 should normally be used as a slave
device, synchronised to an external clock reference.
SAM64 offers a choice of synchronisation sources.
Selection is made from the front panel, and the array
of LEDs confirms the currently-selected source.
The selected source is used as reference for all
four output SRCs, thus ALL audio outputs, both in
AES3-id and MADI formats, will be locked to the
selected reference.
The various clock sources are discussed on the
following page.
Bel Digital Audio Limited
Setting Up & Operation
Block Diagram
Sample Rate Converters
The sampling frequency of the audio data embedded
in SDI video signals is 48 kHz. This is invariant, and
is enshrined in the defining standards for all SDI
formats. As with all operations involving digital audio,
it will generally be desirable for the audio outputs of
the SAM64 to be synchronised (in frequency and/
or phase) with a master reference clock, which will
also synchronise all other digital audio processing in
the facility.
To achieve this, the SAM64 includes four 16-channel
Sample Rate Converters (SRCs), one for each SDI
input (see
Rear Panel Description
on page 8). Each
SRC may be switched in or out by a front panel switch
(see
Front Panel Description on page 7
) or by
external control via the GPIO port. When each SRC
is active, a red LED illuminates, and a tally output
voltage is also available at the rear GPIO port.
When enabled, the SRCs re-clock the audio data
against the sync reference ensuring that the word
blocks in the data are phase-locked exactly to the
reference clock. The SAM64 allows the user to select
a reference clock source to suit the infrastructure of
the facility and the nature of the transfer process.
See following section on “
Synchronisation
”.
Note:
If the SDI inputs are not phase-locked, then no
audio will be present on the MADI output.
Auto-sensing
SDI
De-embedder
SDI 1 – 4 inputs
SDI 1 – 4
Loop-through outputs
Sample rate converters
(with bypass)
AES outputs
SDI Lock LEDs
Local and remote control
of SRCs
Sync References
Inputs & Outputs
SRC On LEDs
MADI Coaxial Output
MADI Optical Output
MADI interface
