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| Hybrid
disc |
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Super
Audio CD |
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Hybrid disc structure
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The
SACD hybrid disc fulfils at once four requirements
of the ISC : it remains a single-sided disc of 12cm
diameter, like usual Compact Disc, and can be played
in current CD-players because of a layer fully
compatible with the 'Red Book' specifications. This
compatibility spares also retailing companies a
double inventory of music titles (existing CDs and
new high-density discs). It is indeed obvious that
the CD format will not disappear immediately after
the introduction of a new high-density audio format.
Finally, a semi-transmissive layer, which contains
high-density data, is glued to the CD layer in order
to offer the highest possible audio quality (point 7
in the ISC specifications).
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As
a result, a conventional CD-player laser will read
through the semi-transmissive layer of a hybrid
disc, while a SACD laser will read the DSD signal
from the semi-transmissive layer.
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Technical
comparison between conventional CD and SACD is
detailed below :
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Conventional
Compact Disc |
Super
Audio CD |
| Diameter |
120mm
(4-3/4") |
120mm
(4-3/4") |
| Thickness |
1.2mm
(1/20") |
2*0.69mm=1.2mm
(1/20") |
Max.
substrate
thickness error |
+/-100um |
+/-30um |
| Signal
sides |
1 |
1 |
| Signal
layers |
1 |
2
: CD-density reflective layer + high-density
semi-transmissive layer |
| Data
capacity |
| Reflective
layer |
| Semi-transmissive
layer |
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| Audio
coding |
| Standard
audio |
| Super
Audio |
| Multi-channel |
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| 16-bit
/ 44.1 kHz |
| 1-bit
DSD / 2.8224MHz |
| 6
channels of DSD |
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| Frequency
response |
5 -
20,000 Hz |
DC(0)
- 100,000 Hz (DSD) |
| Dynamic
range |
96dB
across the audio bandwidth |
120dB
across the audio bandwidth (DSD) |
| Playback
time |
74
minutes |
74
minutes |
| Enhanced
capability |
CD
Text |
Text,
graphics and video |
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The
main idea in hybrid disc format is to combine both
well-known technologies, CD and DVD, respectively to
keep compatibility with the millions of CD players
in the market, and to use the existing DVD-video
process tools to make a two-layers disc, i.e. to add
a high-density layer to a CD reflective layer.
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