24 / 48 page
SigmaTel, Inc.
Data Sheet
STAC9721
24
04/07/00
04/07/00
4.4.6 Record Gain Registers (Index 1Ch)
The 1Ch register adjusts the stereo input record gain. Each step corresponds to 1.5 dB.
The 22.5 dB setting corresponds to 0F0Fh.
The MSB of the register is the mute bit.
When this bit is set to 1, the level for that channel(s) is set at -
∞ dB.
The default value is 8000h, which is to 0 dB gain with mute on.
Table 13. Record Gain Registers
Mute
Gx3… Gx0
Function
0
1111
+22.5 dB gain
0
0000
0 dB gain
1
xxxx
-
∞ gain
4.4.7 General Purpose Register (Index 20h)
This register is used to control some miscellaneous functions. Below is a summary of
each bit and its function. The MS bit controls the MIC1/MIC2 selector, and the MIX bit
controls the Mix/MIC selector. The LPBK bit enables loopback of the ADC output to the
DAC input without involving the AC-Link, allowing for full system performance
measurements.
The 3D bit enables or disables the SS3D speaker separation 3D
enhancement.
Table 14. General Purpose Register
Bit
Function
3D
3D Stereo Enhancement
0 = off, 1 = on
MIX
Mono output select 0 = Mix, 1= MIC
MS
Mic select 0 = MIC1, 1 = MIC2
LPBK
ADC/DAC loopback mode
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