參數(shù)資料
型號(hào)： SAA2502H
廠商： NXP SEMICONDUCTORS
元件分類： 消費(fèi)家電
英文描述： ISO/MPEG Audio Source Decoder
中文描述： SPECIALTY CONSUMER CIRCUIT, PQFP44
封裝： PLASTIC, SOT-307, QFP-44
文件頁(yè)數(shù)： 21/64頁(yè)
文件大?。?/td> 318K
代理商： SAA2502H
1997 Nov 17
21
Philips Semiconductors
Preliminary specification
ISO/MPEG Audio Source Decoder
SAA2502
7.4.8
B
ASEBAND AUDIO PROCESSING
Baseband audio de-emphasis as indicated in the MPEG
input data stream is performed digitally inside the
SAA2502. The included ‘Audio Processing Unit’ (APU)
see Fig.19, may be used to apply programmable
inter-channel crosstalk or independent channel volume
control.
The APU attenuation coefficients LL, LR, RL and RR may
be changed dynamically by the microcontroller, writing
their 8-bit indices to the SAA2502 through its control
interface. The coefficient changes become effective within
one sample period after writing. To avoid audible clicks at
coefficient changes, the transition from the current
attenuation to the next is smoothed. The relationship
between the APU coefficient index and the actual
coefficient (i.e. the gain) is shown in Fig.14 and in Table 9
For coefficient index 0 to 64 the step size is
3
16
dB and
for coefficient index 64 to 255 the step size is
3
8
dB.
The APU has no built-in overflow protection, so the
application must assure that the output signals of the APU
cannot exceed the 0 dB level. For an update of the APU
coefficients, it may be required to increase some of the
coefficients and decrease some others. The APU
coefficients are always written sequentially in a fixed
sequence LL, LR, RL and RR. Therefore, to prevent
(temporary) internal APU data overflow, the following
sequence of steps may be necessary:
1.
Write LL, LR, RL and RR, but change only decreasing
coefficients. Overwrite increasing coefficients with
their old value (therefore do not change these yet).
2.
Write LL, LR, RL and RR again, but now change
increasing coefficients, keeping the other ones
unchanged.
Table 9
APU coefficient index and actual coefficient.
APU COEFFICIENT INDEX C
APU
COEFFICIENT
BINARY
DECIMAL
00000000 to 00111111
0 to 63
01000000 to 11111110
64 to 254
11111111
255
0
2
C
32
------
–
2
32
–
16
)
--C
–
Fig.13 Audio Processing Unit (APU).
handbook, halfpage
audio
samples
LR
LL
RL
left output
audio
samples
right decoded
audio
samples
RR
right output
audio
samples
MGB493
Fig.14 Relation between APU coefficient index and
gain.
(1) Step
3
16
dB per coefficient increment.
(2) Step
3
8
dB per coefficient increment.
handbook, halfpage
MGE480
12
83.25
254 255
(2)
(1)
APU coefficient index
gain
(dB)
64
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