7700 MultiFrame Manual
7721AE4-(B)-HD HDTV 4 Channel AES Audio Embedder
Page-12
Revision
1.5
When
Clean and embed
is selected, all incoming HANC packets and embedded audio data will be
removed; and new audio data will be embedded after EAV. The remaining H blanking period is filled with
default blanking value.
When
Reformat and embed
is selected, pre-existing embedded audio contents will be extracted. All
packets with "Marked Packet for Deletion" or containing the same selected audio groups that are selected
for embedding will be removed. The remaining packets are left justified and new audio will be embedded
after these packets.
5.4.
SELECTING AES LOCKED GROUP MODE
For audio that is synchronous to video there is exactly 8008 audio samples (48kHz sampling rate) in 5
frames of NTSC, 525 line video. Most audio embedders will spread these samples as evenly as possible
throughout the 5 frames of video. Because the 8008 samples do not divide evenly into 5 frames of video,
there is a sequence that only repeats every 5 frames. In all video standards it is possible for the phase of
the audio being embedded by two separate embedders to be out of phase with respect to each other. In
order to transport 8 channels of audio (4 AES pairs) through an embedded link with exactly the same
delay on each channel, both the embedder and the de-embedder must lock the FIFOs of both groups of
audio together. Failing to do so will cause a phase difference between the audio from the two groups.
When the DIP switches are set as shown in Table 5-8, the toggle switch is used to select whether the
embedders will be operated separately or locked together for embedding related audio (such as 5.1
surround sound).
DIP Switch
LED
1 2 3 4 5 6 7 8
Control
Description
Value
Description
1 2 3 4
On On On Off
Off
Off
Off
Off Independent
Groups
Off
Off
Off
Off
Lock Groups
Locked
Groups
On On On On
Table 5-8: Lock Group Mode Switch Settings
When
Independent group
mode is selected, Embedder 1 and Embedder 2 are operated independently of
each other as if two separate embedder devices are being used. The FIFOs are not locked together and
the output phases of the two groups of embedded audio do not have any specific relationship to each
other.
When
Locked group
mode is selected, the Embedder FIFOs are locked together maintaining the phase
relationship between all 4 AES channel pairs in the embedded audio.
"
To maintain a guaranteed audio phase relationship through a complete SDI link, the
audio de-embedder MUST also provide the same locked FIFO management
functionality.
"
For firmware releases 2.3 build 3 and newer, Locked Group mode is ALWAYS active
regardless of the DIP switch setting. Changing the settings will have NO effect on
the mode.
