Sony D8MM-01, Training Manual

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IC643 AOI
The Y and C signals are output by IC351 VFD and then input to IC643
AOI. This IC controls whether A/V signals are input from or output to the
analog video and audio jacks. It also outputs a composite video signal to
IC644 IR Transmitter.
IC644 IR Transmitter
IC644 IR transmitter modulates the audio and video signals it receives
and transmits them through the air using the LEDs on the front of the
camcorder. Sircs data can also be transmitted if a TV input is selected in
the menu.
IC301 SFD
Video Compression
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Discrete Cosine Transform
The shuffled data, which has been formed into compression units, is input
to IC301 SFD. The first step is to perform a DCT (Discrete Cosine Trans-
form) on the data. This process converts the image data into a series of
frequencies. After the transformation you would have one DC compo-
nent and 63 AC components from an 8X8 pixel block. The DC compo-
nent represents the average value of the signal, while the AC compo-
nents represent the amount of change from that value.
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Weighting
This data is then input to a weighting coefficient circuit. This weighting
coefficient mimics the way the human eye perceives picture detail. It
eliminates data that it determines cannot be seen by the human eye.
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Quantization and Variable Length Coding (VLC)
Quantization and VLC (Variable Length Coding) are two distinct sections
that work together to further reduce the amount of data used to represent
video. The number of bits allocated to a picture pattern is evaluated to
prevent distortion. The data is converted to a variable length code that is
between 3 and 16 bits. This is the final step in a compression system that
took the 162Mbps of data and converted it down to 25Mbps.
Audio Signal Baseband Processing
The audio signal is frequency converted so that its sample rate matches
the video signal. The signal will not be compressed.
Audio Signal Interleave
The audio data is interleaved into the video data. However, it is not pro-
cessed by the video compression circuitry. The audio data is held in RAM
so that it is put in the proper position with the video signal. This ensures
that the picture and the voice are in sync.
DV In/Out Transformation
The interleaved audio and shuffled video data is output to IC303 LIP.
IC303 LIP
This IC contains the three layers needed for an IEEE1394 connection.
The three layers are the physical, link and transaction layers. See the
section on IEEE1394 for more details.
IC302 TFD
Data De-shuffling
Now that compression is complete, the data must be put back in its origi-
nal position. This operation is called de-shuffling. When we do this we
reconstruct the ten bands that were created before shuffling. Each of
these bands represents a sub track on the tape.
ECC (Error Correction Code)
The outer parity bits are added to the data. The ECC is Reed-Solomon
Code like that used in CD, Mini-Disc, etc. The inner parity bits are added
later.
Channel Coding
The audio/video data stream has Inner parity, Sync and ID data added to
it. This data is then 24-25 modulated. This is for ATF operation and will
be discussed in more detail in the servo section. After this the outer parity
bits are added. The ITI data is then added to the stream and converted to
scrambled interleaved NRZI (Non Return to Zero Invert) format. This
format uses two bit systems that function alternately and makes it easier
to obtain a stable clock signal during playback.