Digital Signal Processing Reference
In-Depth Information
Table 9.6
Structure of the 17-bit algebraic codebook
Pulse Amplitude
Position
Bits
0
±
1
0, 5, 10, 15, 20, 25, 30, 35
1
+
3
1
±
1
1, 6, 11, 16, 21, 26, 31, 36
1
+
3
2
±
1
2, 7, 12, 17, 22, 27, 32, 37
1
+
3
3
±
1
3, 8, 13, 18, 23, 28, 33, 38,
1
+
4
4, 9, 14, 19, 24, 29, 34, 39
Table 9.7
Innovation pulse gain quantizer table for 8 kb/s
ACELP
Index
0
1
2
3
4
5
6
7
Pulse Gain
0.0
0.15
0.3
0.45
0.6
0.8
1.0
1.2
Index
8
9
10
11
12
13
14
15
Pulse Gain
1.5
1.8
2.1
2.4
2.8
3.2
3.7
4.3
Table 9.8
Bit allocation of 8 kb/s ACELP
for a 20ms frame
Parameters
ACELP 8k
LPC
23
Gain
7
LTP Delay
7
+
7
+
7
+
7
LTP Gain
4
+
4
+
4
+
4
Pulse Locations
13
+
13
+
13
+
13
Pulse signs
4
+
4
+
4
+
4
Pulse Gain
4
+
4
+
4
+
4
Mode
2
Total
160
Where
k
(a constant which controls the gradient of the exponential function)
is 80,
N
(the number of quantizer levels) is 128, and
g
max
and
g
min
are 2720.5
and 0.5 respectively.
9.10.4 Comparison
Three informal listening tests were conducted to assess the speech quality of
the hybrid coder, with transitions quantized at 4 kb/s, 6 kb/s, and 8 kb/s. The
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