AC'97

AC'97 (Audio Codec '97; also MC'97 for Modem Codec '97) is an audio codec standard developed by Intel Architecture Labs in 1997. The standard is used in motherboards, modems, and sound cards.

Audio components integrated into chipsets consist of two component classes: an AC'97 digital controller (DC97), which is built into the I/O Controller Hub (ICH) of the chipset, and AC'97 audio and modem codecs, which are the analog components of the architecture.

AC'97 defines a high-quality, 16- or 20-bit audio architecture with surround sound support for the PC. AC'97 supports a 96 kHz sampling rate at 20-bit stereo resolution and a 48 kHz sampling rate at 20-bit stereo resolution for multichannel recording and playback. AC97 defines a maximum of 6 channels of analog audio output.

Integrated audio is implemented with the AC'97 Codec on the motherboard, a Communications and Networking Riser (CNR) card, or an audio/modem riser (AMR) card.

In 2004, Intel released the successor Intel High Definition Audio (HD Audio) which is not backward compatible with AC'97.^[1] HD Audio has the capability to define many more than AC'97's six output channels, but in practice most motherboards provide no more than 8 channels.

Revisions

AC'97 has had several revisions:^[2]

AC'97 1.x compliant indicates fixed 48K sampling rate operation (non-extended feature set)
AC'97 2.1 compliant indicates extended audio feature set (optional variable rate, multichannel, etc.)
AC'97 2.2 compliant indicates extended audio, enhanced riser audio support, and optional S/PDIF
AC'97 2.3 compliant indicates extended configuration information and optional jack sensing support

AC '97 v2.3 enables Plug and Play audio for the end user. This revision provides means for the audio codec to supply parametric data about its analog interface much like Intel High Definition Audio.

AC-Link

The AC-Link is a digital link that connects the DC97 (the controller) with the audio "codecs." It is composed of 5 wires: the clock (12.288 MHz), a sync signal, a reset signal, and two data wires, namely sdata_out (contains the DC97 output) and sdata_in (contains the codec output). The AC-Link provides a bidirectional (one using sdata_out and the other using sdata_in), fixed bitrate (12.288 Mbit/s), serial digital stream between one controller and several audio codecs.

Each 12.288 Mbit/s stream is divided into 256-bit frames (frame frequency is 48 kHz). This is therefore a time division multiplexing (TDM) scheme.

Every frame is subdivided in 13 slots, from which slot 0 (16 bits) is used to specify which audio codec is talking to the controller. The remaining 240 bits are divided in 12 20-bit slots (slots 1-12), used as data slots.

Each data slot (48 kHz, 20 bits/sample) is used to transmit a raw PCM audio signal (960 kbit/s). Several data slots in the same frame can be combined into a single high-quality signal (maximum is 4 slots, obtaining a 192 kHz, 20 bit/sample, stereo signal).

Since AC-Link is a fixed-frequency link, all sample rate conversion should be performed in the DC97 (controller) or in the software driver.

Codec chips

Codec chips have an AC97 interface on one side and analog audio interface on the other. They are usually small square chips with 48 pins (48-pin QFP package). They are D/A and A/D or only D/A.

Analog Devices AD1819B, 1881A, 1885, 1886, 1887, 1980, 1981, 1985
AKM (Asahi Kasei Microsystems) AK 4540, 4543, 4544A, 4545
Avance Logic (now Realtek) ALC201A, ALC202/A, ALC650, ALC655, ALC658, ALC101, ALC202A, ALC250, ALC850, ALC888
Conexant Cx20468 - with a modem
Cirrus Logic CrystalWare 4236, CrystalClear SoundFusion CS4297, CS4299
Crystal Semiconductors CS4205, CS4202
C-Media CMI9738, 9739, 9761, 9880
ESS ES1988 (with a modem)
Empia EMP202 (2 channel, 20-bit DAC and 20-bit ADC, full duplex AC'97 2.2 compatible stereo audio CODEC)
Intersil HMP9701 (obsolete, 48 kHz fixed samplerate)
National Semiconductor LM4550, LM49321, LM49350, LM49352
Philips UCB 1400 (with touchscreen controller)
Realtek ALC5610 ALC5611^[3]^[4]^[5]
SigmaTel (now IDT) C-Major STAC 9460 (D/A only), 9461, 9462, 9463, 9200, 9202, 9250, 9251, 9220, 9221, 9223, 9750
Silicon Image Si3024 (mono only)
TriTech Microelectronics TR28022, 28026
Yamaha YMF 743, 752, 753
VIA VT1612, VT1616 (VIA Six-TRAC Vinyl Audio), VT82C686
Winbond W83971
Wolfson Microelectronics WM9701, WM9703, WM9704, WM9705 (w/touchscreen), WM9707, WM9708, WM9709 (DAC only), WM9711, WM9712 (w/touchscreen), WM9713 (w/touchscreen), WM9714

Front panel connector

Computer motherboards often provide a connector to bring microphone and headphone signals to the computer's front panel. Intel provides a specification for that header; the signal assignments are different for AC'97 and Intel High Definition Audio headers.^[6]

References

^ "1.2.1 AC'97 Compatibility", High Definition Audio Specification (PDF), Revision 1.0a, Intel Corporation, 2010, p. 17
^ AC'97 Component Specification, Revision 2.3, Intel Corporation, April 2002
^ AC'97 Interface
^ ALC5610 datasheet V1.4
^ ALC5611 datasheet v1.3
^ Intel Corporation (February 2005), Front Panel I/O Connectivity Design Guide (PDF), Version 1.3, pp. 19–25

External links

[1] "1.2.1 AC'97 Compatibility", High Definition Audio Specification (PDF), Revision 1.0a, Intel Corporation, 2010, p. 17

[ac97-2] AC'97 Component Specification, Revision 2.3, Intel Corporation, April 2002

[3] AC'97 Interface

[4] ALC5610 datasheet V1.4

[5] ALC5611 datasheet v1.3

[6] Intel Corporation (February 2005), Front Panel I/O Connectivity Design Guide (PDF), Version 1.3, pp. 19–25

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