STAC9721 datasheet(24/48 Pages) ETC1

24 / 48 page

SigmaTel, Inc.

Data Sheet

STAC9721

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

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 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 Stereo Enhancement

0 = off, 1 = on

MIX

Mono output select 0 = Mix, 1= MIC

Mic select 0 = MIC1, 1 = MIC2

LPBK

ADC/DAC loopback mode

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