STAC9708 datasheet(30/56 Pages) ETC

30 / 56 page

SigmaTel, Inc.

Preliminary

STAC9708/11

10/02/98

4.4.6 Record Gain Registers (Index 1Ch)

The 1Ch register adjusts the stereo input record gain. Each step corresponds to 1.5 dB. 22.5 dB

corresponds to 0F0Fh and 000Fh respectively. 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 corresponds to 0 dB gain with mute on.

Table 14. Record Gain Registers

MUTE

Gx3… Gx0

FUNCTION

1111

+22.5 dB gain

0000

0 dB gain

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 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.

Table 15. General Purpose Register

BIT

FUNCTION

3D Stereo Enhancement on/off 1 = on

MIX

Mono output select 0 = Mix, 1= Mic

Mic select 0 = Mic1, 1 = Mic2

LPBK

ADC/DAC loopback mode

4.4.8

3D Control Register (Index 22h)

This register is used to control the 3D stereo enhancement function, Sigmatel Surround 3D (SS3D),

built into the AC'97 component. Note that register bits, DP1-DP0 and DPR1-DPR0 are used to control

the separation ratios in the 3D control for both LINE_OUT and DAC_OUT respectively. This allows

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