| Hybrid
disc |
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Super
Audio CD |
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Hybrid disc structure
(cont.)
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Margins
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More
severe disc production margins contribute a factor
1.35 times on the account of radial margins and a
factor of 1.31 times on the account of tangential
margins. Indeed, additional gain in physical density
had to be met by reducing the margins in the SACD
system, as compared with CD. The relative track
pitch (= track pitch / spot diameter) is reduced by
a further factor of 1.35 and the relative channel
bit length (= channel bit length / spot diameter) is
reduced by a further factor of 1.31. Tighter
production tolerances are therefore required for
discs and drives. Years of experience in CD
manufacturing have however put these well within the
capabilities of today's production facilities.
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All
the above factors together result in a total
physical density increase of 4.54 times.
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Due
to the higher tangential density, the EFM bandwidth
is relatively closer to the optical cut-off
frequency than in the case of CD. Therefore, the
amplitudes of the highest EFM frequencies are
smaller compared to the 'eye pattern' of CD.
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Comparison of pits
and eye patterns between CD and SACD
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More
efficient channel modulation (EFM+ and deleting the
subcode), error correction (RSPC) and Sector format
(with greatly reduced sector overhead) achieve a
gain of 1.12, 1.16 and 1.14 respectively, resulting
in an additional data density increase of 1.49
times. The better error correction capabilities are
mostly due to new coding algorithm and increased
power processing.
The following chapters
provide detailed information on sector
format, error correction and channel modulation.
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Finally, a slightly
larger (1.02 times) program area gives the
high-density layer a total capacity gain of 6.9
times over the CD layer.
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The
table below gives the values of the technical
characteristics for each layer (CD and high-density)
of a SACD hybrid disc, as well as the density gain
factor which may result from these parameters.
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| Parameter |
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CD
Red Book compatible layer |
Super
Audio CD layer |
Gain
factor |
| Reflectivity |
|
Reflective |
Semi-transmissive |
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| Capacity |
|
680MB |
4.7GB |
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| Laser
wavelength |
|
780+/-10nm |
650+/-5nm |
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| Polarisation |
|
Circular |
Circular |
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| Pick-up
lens Num. Aperture |
|
0.45+/-0.01 |
0.60+/-0.01 |
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| Max.
disc tilt |
|
0.6° |
0.4° |
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| Spot
diameter |
w=l/(2*NA) |
0.78/(2*0.45)=0.87 |
0.65/(2*0.60)=0.54 |
1.60(1) |
| Track
pitch |
p |
1.6mm |
0.74mm |
2.16 |
| Relative
radial density |
=p/w |
1.85 |
1.37 |
1.35(2) |
| Channel
bit length |
c |
0.28mm |
0.133mm |
2.10 |
| Minimum
Pit/Land Length (3T) |
=3*c |
0.83mm |
0.40mm |
2.10 |
| Relative
tangential density |
=3*c/w |
0.97 |
0.74 |
1.31(2) |
| Density |
d=p*c |
0.45mm2/ch.bit |
0.1mm2/ch.bit |
4.54(3) |
| Linear
velocity |
v |
1.21m/sec |
3.49m/sec |
2.88 |
| Optical
cut-off frequency |
fco=v/w=v*2*NA/l |
1.47MHz |
6.44MHz |
4.6 |
| Channel
bit rate |
f=v/c |
4.3218MHz |
26.16MHz |
6.05 |
| Highest
EFM freq. |
fI3=f/6 |
0.72MHz |
4.36MHz |
6.05 |
| Relative
badwidth |
=fI3/fco |
0.52 |
0.68 |
1.31(4) |
| Encoding
efficiency |
e |
28.4% |
42.3% |
1.49 |
| User
data bit rate |
=f*e |
1.2288Mbit/sec |
11.08Mbit/sec |
9.0 |
| Data
area inner radius |
|
25mm |
24mm |
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| Data
area outer radius |
|
37.5/58mm |
38/58mm |
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| Max.
radial run-out |
|
140mm |
100mm |
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| Size
of program area on disc |
a=p*(Rmax2-Rmin2) |
25-58mm=8600mm2 |
24-58mm=8760mm2 |
1.02 |
| User
data capacity |
=(a/d)*e |
682Mbytes |
4700Mbytes |
6.9 |
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(1)
The smaller spot size increases the optical
resolution, without sacrificing system margins
(2) Both the higher relative radial density and
higher relative tangential density reduce system
margins
(3) Total increase of physical density is composed
of :
(gain in spot area)*(gain in relative radial
density)*(gain in relative tangential density)
= (1.6)2*1.35*1.31=4.5
(4) gain in relative bandwidth = gain in relative
tangential density
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