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AC'97

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AC'97 (short for Audio Codec '97; also MC'97, short for Modem Codec '97) is Intel Corporation's Audio "Codec" standard developed by the Intel Architecture Labs in 1997, and used mainly in motherboards, modems, and sound cards.

Intel's use of the word audio codec refers to signals being encoded/decoded to/from analog audio from/to digital audio, thus actually a combined audio AD/DA-converter. This should not be confused with a codec in the sense of converting from one binary format to another, such as an audio (MP3) or video (Xvid) codec in a media player.

Audio components integrated into chipsets consists of two components: an AC'97 digital controller (DC97), which is built into the I/O Controller Hub (ICH) of the chipset, and an AC'97 audio and modem codecs, which is the analog component of the architecture. AC'97 defines a high-quality, 16- or 20-bit audio architecture with surround sound support for the PC that is used in the majority of today's desktop platforms. AC'97 supports 96,000 samples/second in 20-bit stereo resolution and 48,000 samples/second in 20-bit stereo for multichannel recording and playback.

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In 2004 AC'97 was superseded by Intel High Definition Audio (HD Audio).


Revisions[1]

  • 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.

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. They are D/A and A/D or only D/A.

  • Analog Devices AD1819B, 1881A, 1885, 1886, 1887, 1980, 1981, 1985 (Obsolete)
  • AKM (Asahi Kasei Microsystems) AK 4540, 4543, 4544A, 4545
  • Avance Logic (now Realtek) ALC201A, ALC202/A, ALC650, ALC655, ALC658, ALC101, ALC202A, ALC250, ALC850
  • 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 LM 4540, 43, 45, 46, 48, 49, 50
  • Philips UCB 1400 (with touchscreen controller)
  • Realtek ALC658, ALC655, ALC650, ALC268
  • 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

References

  1. ^ AC'97 Component Specification, Revision 2.3, Intel Corporation, April 2002

See also

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