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Linear Acoustic LA-5448 AC-3 Frame Synchronizer/Rate Shaper User Guide
4.1
Main Menu Level
Referring to the menu tree on the preceding page, it can be seen that the Main Menu level
can be scrolled through using either the left or right arrows. The choices are: Version, Sta-
tus, Statistics, and Setup, each of which have sub menus (except the version screen). The
submenus can be accessed by pressing the down arrow. Note that both the Status and Sta-
tistics screens are informational and have no adjustments.
4.1.1
Status Menu
Upon booting, the Version screen in briefly displayed then switched to the Status Menu.
The Status Menu shows the data rate for the AC-3 signals applied to each of the four Main
Inputs, and displays dashes (----) for programs that are not present.
Pressing the Down arrow will step through each of the four main input programs,
showing the input data rate, followed by the audio coding mode (acmod) metadata
parameter, followed by the output data rate. If Stream Shaping is disabled, the input
and output data rates will match. If Stream Shaping is enabled, the output data rate
will be fixed at 448 kbps.
4.1.2
Statistics Menu
The Statistics menu provides more detailed information about the health of each of the
input signals applied to the LA-5448. The main status LEDs on the front panel give the
first indication of trouble when illuminated red, while further details about the error con-
dition can be found under this menu. Currently, the CRC of the AES carrier is counted
and displayed and future revisions will expand this to show details of the AC-3 CRCs con-
tained within each AES input.
As a general rule of thumb, the AES CRC indicates interface issues stemming from the cor-
ruption of the physical AES interface. These types of errors are most likely due to prob-
lems such as clocking, termination, or asynchronous switching. The AC-3 CRC is useful
for determining upstream issues where the physical interface may be valid but clicking or
popping might be heard after decode as the AC-3 packets are being damaged. The cause
of an inner-interface issue such as this can stem from many things, but one likely suspect
is a satellite receiver that is losing lock due to rainfade or other RF issues- the AES carrier
may still be present as it is generated locally, but its AC-3 payload could be damaged or
missing.
4.1.3
Setup Menu
This menu contains settings for the main digital audio I/O as well as a method to restore
factory defaults. To adjust a particular parameter, simply rotate the rotary encoder knob
until the desired value is displayed. An asterisk (*) is also displayed noting that the change
will be made and stored to memory when the Right (Next) front panel button is pressed.
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Menus
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