Audio Codec '97

AC ‘97 Component Specification Revision 2.3 Rev 1.0

• Amplified analog stereo headphone output (HP_OUT) transmitted to headphones or headset via stereo

mini-jack.

• Discrete analog 4-channel output (LINE_OUT plus 4CH_OUT) transmitted to Front and Surround

amplified stereo PC speaker arrays via dual stereo mini-jacks.

• Analog matrix-encoded Surround output (such as Dolby ProLogic**) transmitted via stereo line level

output jack (LNLVL_OUT) to consumer A/V equipment which drives a home theater multi-speaker array.

• Digital 5.1 channel output (such as Dolby Digital AC-3*) transmitted via S/PDIF (SPDIF_OUT) to digital

ready consumer A/V equipment which drives a home theater multi-speaker array.

5.2 LINE_OUT and AUX_OUT

AC ‘97 audio Codecs support two independently controlled stereo outputs:

The master output, labeled LINE_OUT, uses pins 35, 36 for L and R (48 pin QFP package) and is

controlled by the Master Volume Register 02h. No changes have been made to LINE_OUT definitions.

A second output, originally defined as HP_OUT, uses pins 39, 40, and 41 for L, Common, and R (48-pin

QFP package) was re-defined as LNLVL_OUT for AC ‘97 2.1, and is controlled by optional volume

41 for the additional (i.e. L & R Surround) outputs.

5.2.1 AUX_OUT Options

As identified in the previous section, there are three common uses for AC ‘97’s second output. AC ‘97 2.2

addresses all three uses by renaming the second output as AUX_OUT, Register 04h as Aux Out Volume, and the

pins as AUX_OUT_L, AUX_OUT_C, and AUX_OUT_R.

Driver developers should be aware that the AC ‘97 AUX_OUT may be implemented in one of three ways:

True line level out. Support for a consumer equipment-compatible (10 kΩ) line level output that does not

change with master volume settings. Either fixed or fixable via the independent volume controls in Register

04h, the output level provides a 1V RMS (2.8 V peak-to-peak) output level for a 0 dB gain PCM output

stream. When implemented this way, AUX_OUT is equivalent to AC ‘97 2.1’s LNLVL_OUT definitions.

Headphone out. AUX_OUT can be implemented to support integrated headphone amplifier with 32 Ω

drive capability and independent volume control via Register 04h. When implemented this way,

AUX_OUT is equivalent to AC ‘97 1.03 original HP_OUT definitions

4-Channel out. In Codecs that support 4-channel operation, AUX_OUT can be implemented to support the

additional (i.e. L&R Surround) outputs. When implemented this way, AUX_OUT will be referred to

4CH_OUT. In 4CH_OUT implementations, L and R Surround output is controlled via Surround Volume

AUX_OUT defaults to be LNLVL_OUT unless HP_OUT or 4CH_OUT support is detected. Unless the specific

Codec configuration is indicated via INF file, driver writers should use the following methods for detecting a

specialized Codec with HP_OUT or 4CH_OUT capabilities:

• HP_OUT capability can be detected via Reset/ID Register 00h, ID bit 4 and the Aux Out Volume Register

04h default value reads “8000h” (i.e. implemented). ID4 is no longer used to indicate LNLVL support.

• 4CH output capability can be detected via the Extended Audio ID Register 28h, SDAC ID bit 7, and a

Surround Volume Register 38h default of “8080h” (i.e. implemented).

HP and LNLVL implementations of AUX_OUT external output are powered down via bit PR6 in Register 26h.

5.3 Audio Sampling Rate Support (Fixed, Variable, and Double)

Fixed 48 kHz audio. All AC ‘97 audio Codecs support 48 kHz fixed sample rate operation, which relies on the

Controller or software driver for any sample rate conversion (SRC) capabilities.

Variable rate audio. Variable sample rate audio extends the AC ‘97 architecture to address host-based solutions,

similar to those appearing on USB, by minimizing the SRC burden for the primary audio stream. High quality

digital SRC and mixing support for both 44.1 and 48 kHz content remain key requirements for supporting multiple