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7700 MultiFrame Manual
7735AVC-LB Video Composite Encoder and Audio DAC with SoftSwitch
7.7.3. Error Detection and Handling (EDH) Error Duration
Fault definitions
EDH error duration
NA
1 to 127 fields
7.7.4. Detecting Audio Over Level Faults
The Over level and Over duration controls are used to detect when an audio amplitude is close to a
dangerous level (i.e. clipping a downstream device, or saturating the digital word length). The Over level
control sets the audio level over which there is considered to be a fault. The audio must be over this level
for the duration set by the Over duration control before the fault condition exists. A fault will be generated
when any channel has generated an over condition.
7.7.4.1. Setting the Audio Over Level
Fault definitions
Over level
-30dB to 0dB FS in
1/4dB increments
-6dB FS
7735AVC-LB - 28
A check sum is calculated for every field of video and compared to the
same EDH check sum transmitted in the vertical interval. If the check
sums do not match, then there was at least one bit error in the active
picture area of the image.
This control enables the user to set an error condition when a number of
consecutive fields contain EDH errors. If set to NA, this type of fault
detection is turned off. If set to 1, any "Error Detection and Handling"
(EDH) error will generate an error while large numbers (>20) will
effectively check the presence/absence of EDH encoding.
If the video signal has passed through hardware that has modified the
picture (i.e. a vision mixer) without re-calculating the EDH check sums,
then both full field and active picture errors will be generated. In that
case, disable both full field and active picture error detection in the "Fault
Definitions" above.
If the video signal has passed through hardware that has modified the
ANC data area (i.e. audio multiplex) without re-calculating the EDH check
sums, then full field errors will always be generated. In that case, disable
full field error detection and use active picture only.
Fore more information on Error Detection and Handling, see SMPTE RP-
165.
This control sets the audio level over which there is considered to be over
level. This value is expressed in dB full scale (FS) and can even be used
to detect digital clipping. If set to 0 dB FS, then if 3 or more consecutive
samples (set with the duration control) are at digital saturation (max or
min), then the digital word length has been exceeded.
Revision 1.6
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