Production Data
WM8945
Figure 27 DSP/PCM Mode Audio Interface (mode B, LRCLK_INV=0, Slave)
COMPANDING
The WM8945 supports A-law and -law companding on both transmit (ADC) and receive (DAC) sides
as shown in Table 45. Companding converts 13 bits (-law) or 12 bits (A-law) to 8 bits using non-
linear quantization. This provides greater precision for low amplitude signals than for high amplitude
signals, resulting in a greater usable dynamic range than 8 bit linear quantization.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R5 (05h)
DAC_COMP
DAC Companding Enable
0 = Disabled
3
0
Companding
control
1 = Enabled
2
1
0
DAC_COMP
MODE
0
0
0
DAC Companding Mode
0 = µ-law
1 = A-law
ADC_COMP
ADC Companding Enable
0 = Disabled
1 = Enabled
ADC_COMP
MODE
ADC Companding Mode
0 = µ-law
1 = A-law
Table 45 Companding Control
Companding uses a piecewise linear approximation of the following equations (as set out by ITU-T
G.711 standard) for data compression:
-law (where =255 for the U.S. and Japan):
F(x) = ln( 1 + |x|) / ln( 1 + )
Table 1 law (where A=87.6 for Europe):
F(x) = A|x| / ( 1 + lnA)
} for -1 ≤ x ≤ 1
for x ≤ 1/A
F(x) = ( 1 + lnA|x|) / (1 + lnA)
for 1/A ≤ x ≤ 1
PD, May 2011, Rev 4.1
69
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