DAI-3206 Instruction Book
Revision 6
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Page 8 of 12
3206-DAI_ib_Rev6.doc
Description of
DAI-3206 Modes:
Overview:
The DAI-3206 supports several insertion modes to provide flexibility in the studio environment. These modes
determine the input (AES or Analogue audio) and sampling reference. The DAI-3206 was originally designed to
support the new compressed digital audio formats such as Dolby-E, which must pass unchanged from origin to
destination. This required that the DAI-3206 supported asynchronous 48K plus associated control packet. This
control packet is only optional for synchronous 48kHz mode.
It was also decided that the channel pairs might be either both AES, Analogue or a combination of the two. In the
combined AES/analogue case, the analogue audio is locked to the AES if present of locked to video if the AES is
lost.
AES audio can be resampled to become synchronous with the video, however, a small but measurable degradation
of performance occurs, which in almost all cases is insignificant. Additionally, the channel data is destroyed and
subsequently partially rebuilt. However, performing this resampling allows the audio data to become 48K
synchronous and more flexible when used with other studio equipment.
MODE 0 (Asynchronous AES1 & AES2)
This mode is used when perfect AES transfer is required. This is most useful for Dolby-E type applications,
otherwise MODE 4 is recommended. In this mode the data is asynchronously distributed which is not compatible
with synchronous decoders unless the AES is already synchronized to video at the AES encoder. Additionally, some
AES decoders employ a minimal sample buffer implementation; this is done for several reasons, primarily in tape
recorders, which try to minimize coding delay. This delay accumulates over multiple play modify and record
operations which may finally result in annoying lip sync.
MODE 1&2 (Asynchronous AES & Analogue Audio)
This mode is used when perfect AES transfer is required. The analogue audio is sampled using the AES input as a
reference. If the AES is missing, then the analogue audio is synchronous to the video. However, this distribution is
even and no attempt to compensate (pre-load the receiver buffer) for the absence of audio packets during in the
vertical interval is performed. Most receivers such as the DAX-3206 contain a buffer structure that easily handles
this distribution. You may be aware of the audio packet distribution differences between the SMPTE & SONY
formats. The DAX-3206 was designed with a buffer capable of tolerating either distribution.
MODE 3 (Synchronous Analogue Audio)
This mode is probably the most confusing and it is not recommended in favour of MODE 7. This was the original
distribution mode of the DAI-3206. In this mode the audio is synchronous to the video, however, no attempt to
compensate (pre-load the receiver buffer) for the absence of audio packets during in the vertical interval is
performed. The DAX-3206 was designed with a buffer capable of tolerating many sample distributions.
MODE 4 (Resampled AES1 & AES2)
With the advent of high performance digital audio receivers many synchronization issues can be eliminated. The
advantage is that the audio is now synchronized to the video with little loss of performance. The disadvantage is
the channel data is lost and is therefore rebuilt. This is not an issue in practice and is mentioned for completeness.
To fully complement minimal buffer management practices in some studio video recorders, the packet distribution
has been completely changed from previously described distributions. A fixed packet distribution is generated that
is identical to SDI test signal generators known to be acceptable to studio VCRs. This distribution compensates for
the absence of audio packets in the vertical switching region.
MODE 5&6 (Asynchronous AES & Analogue Audio)
This mode treats the AES as in MODE 4, with the analogue audio following the sample fixed distribution.
MODE 7 (Synchronous Analogue Audio)
This is the recommended analogue input mode that uses the same fixed distribution as described in MODE 4.
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