AC'97
AC'97 is an audio codec standard developed by Intel Architecture Labs and various codec manufacturers in 1997. The standard was used in motherboards, modems, and sound cards.
The specification covers two types of components, and the AC-Link digital interface between them:
- an AC'97 digital controller, which is typically built into the southbridge of the chipset, and
- an AC'97 audio and/or modem codec, available from several vendors, which contains the analog components of the architecture.
Integrated audio is implemented with the AC'97 Codec on the motherboard, a communications and networking riser card, or an audio/modem riser card.
The first shipping system was in the Cyrix MediaGX, in 1997. Intel started shipping the initial I/O Controller Hub support in 1999, and it was not until public shaming in 2000, that most PC OEMs started shipping AC'97 audio as the default.
In 2004, Intel released Intel High Definition Audio which is a successor that is not backward compatible with AC'97. HD Audio has the capability to define up to 15 output channels, but in practice most motherboards provide no more than 8 channels.
Revisions
AC'97 has had several revisions:- AC'97 1.x compliant indicates fixed 48 kHz sampling rate operation
- AC'97 2.1 compliant indicates extended audio feature set
- AC'97 2.2 compliant indicates extended audio, enhanced riser audio support, and optional Sony/Philips Digital Interface Format
- AC'97 2.3 compliant indicates extended configuration information and optional jack sensing support
AC-Link
The AC-Link is a digital link that connects the DC97 with the audio codecs. It is composed of five wires: the 12.288 MHz, a 48 kHz signal, a signal, and two data wires which carry the actual audio data: and. The first four are outputs from the controller, while carries input from the codec. The link carries a bidirectional serial data stream at a fixed bitrate between the controller and one or more codecs.Each 12.288 Mbit/s stream is divided into 256-bit frames. This is therefore a time-division multiplexing scheme.
Every frame is subdivided in 13 slots. The first is 16 bits long and contains validity flags for the remaining slots, while the remaining 240 bits are divided in twelve 20-bit slots, used as data slots.
Slots 1, 2 and 12 are used for non-audio data, while slots 3-11 carry up to nine channels of raw pulse-code modulation audio signals. Normally, six channels are used for 5.1 surround sound, and three channels are available for modem use. However, slots can be combined to provide a 96 kHz sampling rate for the L, R and C channels.
Lower sample rates are implemented using a handshake protocol between the controller and codec which skips data during certain frames.
Codec chips
Codec chips have an AC'97 interface on one side and analog audio interface on the other. They are usually small square chips with 48 pins. They are D/A and A/D or only D/A.- Analog Devices AD1819B, AD1881A, AD1885, AD1886, AD1887, AD1980, AD1981, AD1981A, AD1985. Since then, ADI have gotten out of the PC audio business, either obsoleting or selling off devices to Conexant.
- AKM (Asahi Kasei Microsystems) AK 4540, 4543, 4544A, 4545
- Avance Logic ALC201A, ALC202/A, ALC650, ALC655, ALC658, ALC101, ALC202A, ALC250, ALC850, ALC888
- Conexant Cx20468 – with a modem
- Cirrus Logic CrystalWare 4236, CrystalClear SoundFusion CS4297, CS4299
- Creative Technology
- Crystal Semiconductors CS4205, CS4202
- C-Media CMI9738, 9739, 9761, 9880
- ESS ES1988
- Empia EMP202
- Integrated Device Technology
- Intersil HMP9701
- National Semiconductor LM4550, LM49321, LM49350, LM49352
- Philips UCB 1400
- Realtek ALC5610 ALC5611
- SigmaTel C-Major STAC 9460, 9461, 9462, 9463, 9200, 9202, 9250, 9251, 9220, 9221, 9223, 9750
- Silicon Labs Si3036, Si3038, Si3046, Si3048
- TriTech Microelectronics TR28022, 28026
- Yamaha YMF 743, 752, 753
- VIA VT1612, VT1616
- Winbond W83971
- Wolfson Microelectronics WM9701, WM9703, WM9704, WM9705, WM9707, WM9708, WM9709, WM9711, WM9712, WM9713, WM9714