Installation manual
Hardware installation2–49
Reference Modes
The DAB must have an external reference signal to provide synchronous operation. A rotary DIP switch is provided to
select one of seven possible sync modes (for the location of this switch, see page 2–41).
The audio matrix can be synchronized using an AES/EBU reference signal, or, an NTSC or PAL video reference signal.
The standard and preferred method is to use an AES/EBU audio reference signal, because the DAB can provide precise
locking and time alignment to an AES/EBU reference that is not possible with a video reference. If the AES/EBU refer-
ence is used, it must be connected to the three pin “AES REF IN” connector (as shown on page 2–47). For the video matrix
(ABX 3500 or DBX 3500), a video reference would be connected to the “REF” BNC connector (above the “Alarm”
BNC).
†
If a video reference is to be used for the digital audio sync reference, this signal should be looped through the two “REF”
BNCs and connected to the video “REF” BNC (terminating).
The choices for reference modes are as follows:
S 48 kHz narrow
S 48 kHz NTSC video
S 48 kHz PAL video
S 48 kHz internal
S 48 kHz AES auto (recommended setting) (factory set and shipped in this position)
S AES automatic
S AES vari speed
The following section describes each of the options in detail:
48 kHz Narrow. This mode provides an ultra stable low–jitter reference at a sample rate of 48 kHz. The lock range of
the internal PLL is approximately + or – 200 ppm. When unlocked, the internal frequency defaults to 48 kHz. This mode
is normally used only for testing in the factory but could be used when an ultra stable reference is available.
48 kHz NTSC Video. This mode utilizes a local video PLL locking to Horizontal sync which is then compared to a di-
vided down version of the internal 12.288 MHz clock. The 12.288 MHz clock is generated by a low–jitter secondary
PLL which provides approximately equivalent performance to the AES low–jitter PLL. This is a frequency lock only
and does not attempt to define a specific relationship between video frames and audio frames. When unlocked, the inter-
nal frequency defaults to 48 kHz.
48 kHz PAL Video. This mode utilizes a local video PLL locking to Horizontal sync which is then compared to a divided
down version of the internal 12.288 MHz clock. The 12.288 MHz clock is generated by a low–jitter secondary PLL which
provides approximately equivalent performance to the AES low–jitter PLL. This is a frequency lock only and does not
attempt to define a specific relationship between video frames and audio frames.
48 kHz Internal. This allows the internal low–jitter PLL to run without external reference. A trimmer is set at the factory
for correct center frequency. Normally this mode is used only for factory testing. (This mode forces all inputs to be
asynchronous to the internal reference.)
†
Although any constant APL color test signal may be used for sync, the preferred video reference signal is analog black burst.