Digital Signal Processing Reference
In-Depth Information
Table 9.5
Bit allocation for a 20ms frame
Parameters
White noise Harmonic ACELP 4k
ACELP 6k
LPC
23
23
23
23
Pitch
-
8
-
-
PPL
-
7
-
-
PPS
-
4
-
-
Amplitudes
-
14
+
14
-
-
Gain
5
3
+
5
3
3
LTP Delay
-
-
7
+
7
7
+
7
+
7
+
7
LTP Gain
-
-
4
+
4
4
+
4
+
4
+
4
Pulse Locations
-
-
10
+
10
8
+
8
+
8
+
8
Pulse Signs
-
-
2
+
2
1
+
1
+
1
+
1
Pulse Gain
-
-
3
+
3
3
+
3
+
3
+
3
Mode
2
2
2
2
Total
30
80
80
120
or odd, and four bits are required to transmit the location. The signs of the
two pulses are forced to be opposite in the error minimization process, hence
only the sign of the first pulse is transmitted, using one bit. The pulse gain
and the common normalization factor of the frame are quantized using three
bits each (see Table 9.4).
9.10.3 TransitionQuantizationwith8kb/sACELP
The 8 kb/s version uses 5ms sub frames. For each subframe the LTP delay,
LTP gain, locations, signs, and the gain of four innovation pulses are transmit-
ted. The pulse gain terms of the four subframes are normalized with respect
to the quantized
rms
energy of the speech signal and the normalization factor
is transmitted for each 20ms frame. Table 9.8 shows the bit allocation of the
8 kb/s ACELP parameters. The LTP delay and gain are quantized in the same
way as the 4 kb/s version, using seven bits and four bits, respectively.
The locations and the signs of the four pulses are shown in Table 9.6.
The pulse gain of each subframe is quantized using four bits, as shown in
Table 9.7. The common normalization factor, i.e. the
rms
energy of the original
speech signal, in each frame is logarithmically quantized using seven bits,
and the quantized value,
g
rms
i
, is given by,
k
g
max
i
−
g
min
+
k
N
−
1
g
rms
i
=
−
+
=
−
k
g
min
for
i
0
,
1
, ... ,N
1 (9.70)
k
Search WWH ::
Custom Search