MAS 35x9F
DATA SHEET
3.3.7. DSP Volume Control
Table 3–14: Settings for the digital volume matrix
The digital baseband volume matrix is used for control-
ling the digital gain as shown in Fig. 3–3. This volume
control is effective on both, the digital audio output and
the data stream to the D/A converters. The values are
in 20-bit 2’s complement notation.
Memory
Name
D0:354 D0:355 D0:356 D0:357
LL
LR
RL
RR
Stereo
−1.0
0
0
−1.0
(default)
Table 3–14 shows the proposed settings for the 4 vol-
ume matrix coefficients for stereo, left and right mono.
Mono left
−1.0
−1.0
0
0
The gain factors are given in fixed point notation
19
Mono right
0
0
−1.0
−1.0
(−1.0×2 = 80000 ).
hex
If channels are mixed, care must be taken to prevent
clipping at high amplitudes. Therefore, the sum of the
absolute values of coefficients for one output channel
must be less than 1.0.
3.3.8. Explanation of the G.729A Data Format
The codec is working on a page basis where the
encoding and decoding is performed in blocks of 50
G.729 frames, whereas each frame consists of
10 bytes in byte-swapped order (see Fig. 3–4). There-
fore most changes to the UserControl register become
effective when processing of the current page is fin-
ished. The pages are optionally preceeded by 10 byte
header frames (see Table 3–15).
For normal operating conditions it is recommended to
use the main volume control of the audio codec
instead (register 00 10
of the audio codec).
hex
left audio
+
−1
LL
Table 3–15: Content of page header
−1
−1
LR
RL
Byte
1
2
3
4
5
6
7
8
9
10
Value 64 6d 72 31 64 61 74 61 F4 01
(hex)
Switching directly from encoding to decoding mode (or
vice versa) is not allowed. Instead, the controller has to
send a stop request to the MAS 35x9F (writing 0
to
hex
+
UserControl) and must keep on sending data in decod-
ing mode or receive data in encoding mode until the
current page of 50 frames is finished. After this run-out
time, the encoding or decoding can be started again.
−1
RR
right audio
Fig. 3–3: Digital volume matrix
page frame frame frame
frame frame page frame frame
49 49 header 51 52
frame frame page frame frame
99 100 header 101 102
...
...
...
header
1
2
3
10 ms
10 ms
...
...
byte byte byte byte byte byte byte byte byte byte
10
64 6D 72 31 64 61 74 61 F4 01
2
1
4
3
6
5
8
7
9
Fig. 3–4: Schematic timing of the data transmission with preceeding header
44
June 30, 2004; 6251-505-1DS
Micronas
MICRONAS [ MICRONAS ]
