AN1250 STMicroelectronics, AN1250 Datasheet - Page 7

• Manufacturer Part Number: AN1250
• Description: STA014/STA015 MPEG LAYER III DECODER AND ADPCM CODEC
• Manufacturer: STMicroelectronics

Table 5. Mode 3 (G721, 16kHz, 8 bit mono) configuration
4. ADPCM FRAME PACKING
The STA014/STA015 can pack ADPCM encoded sample into frames for fast error recovering and fast forward
capability. The frame size may be adjusted to match a trade-off between the bit rate overhead and the frame
length. Any of the 4 algorithms may use the frame capability in stereo or mono encoding: bit AFM_EN of
ADPCM_CONFIG register enable or disable this feature. The frame size (in bytes) can be computed as follow:
Where AFS is the value programmed into the ADPCM_FRAME_SIZE register.
The frame always starts with a 12 bytes common header for both DVI and G726 pack and is followed by either:
The 12 bytes header structure has the layout shown in Table 6 Frame header structure. Table 7 gives an ex-
ample of the relationship between the ADPCM frame size and the corresponding bitrate overhead at the encod-
er output, assuming a compression ratio equal to 4 and a 16kHz 16 bit mono input bitstream.
Table 6. Frame header structure
– 6 bytes when DVI algorithm is selected
– 96 bytes when G726 pack algorithm is selected
Index
0..4
5..7
10
11
8
9
Address
185
184
114
16
83
77
19
ADPCM configuration
Sample frequency
Frame counter
Description
Sample size
Frame size
Sync word
ADPCM_SAMPLE_FREQ
ADPCM_CONFIG
Frame size = (AFS * 90) + 108
GPSO_ENABLE
SOFT_RESET
CHIP_MODE
Name
PALY
RUN
AN1250 APPLICATION NOTE
ADPCM_SAMPLE_FREQ
ADPCM_FRAME_SIZE
ADPCM_CONFIG
0x5354445649
ADC_WLEN
Content
2 (encoder mode)
3 (decoder mode)
0 (encoder mode)
1 (decoder mode)
Value
10
1
1
8
1
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