AC'97 (''Audio Codec '97;'' also MC'97 for ''Modem Codec '97'') is an

audio Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to: Sound * Audio signal, an electrical representation of sound *Audio frequency, a frequency in the audio spectrum * Digital audio, representation of sou ...

codec A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder. In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or ...

standard developed by Intel Architecture Labs in 1997. The standard was used in motherboards,

modem A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulati ...

s, and

sound card A sound card (also known as an audio card) is an internal expansion card that provides input and output of audio signals to and from a computer under the control of computer programs. The term ''sound card'' is also applied to external audio ...

s. The specification covers two types of components, and the AC-Link digital interface between them: # an AC'97 ''digital controller'' (DC97), which is built into the southbridge of the

chipset In a computer system, a chipset is a set of electronic components in one or more integrated circuits known as a "Data Flow Management System" that manages the data flow between the processor, memory and peripherals. It is usually found on the mo ...

, and # an AC'97 audio and modem ''codec'', available from several vendors, which contains the analog components of the architecture. AC'97 defines a high-quality, 16- or 20-

bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...

audio architecture with

5.1 surround sound 5.1 surround sound ("five-point one") is the common name for surround sound audio systems. 5.1 is the most commonly used layout in home theatres. It uses five full bandwidth channels and one low-frequency effects channel (the "point one"). Dol ...

support for the PC. AC'97 supports a 96 kHz

sampling rate In signal processing, sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave to a sequence of "samples". A sample is a value of the signal at a point in time and/or s ...

at 20-bit stereo resolution and a 48 kHz sampling rate at 20-bit stereo resolution for multichannel recording and playback. Integrated audio is implemented with the AC'97 Codec on the motherboard, a

communications and networking riser Communications and networking riser (CNR) is a slot found on certain PC motherboards and used for specialized networking, audio, and telephony equipment. A motherboard manufacturer can choose to provide audio, networking, or modem functionality in ...

card, or an

audio/modem riser The audio/modem riser (AMR) is a riser card, riser expansion slot found on the motherboards of some Pentium (brand), Pentium III, Pentium 4, Duron, and Athlon personal computers. It was designed by Intel to interface with chipsets and provide an ...

card. In 2004, Intel released

Intel High Definition Audio Intel High Definition Audio (IHDA) (also called HD Audio or development codename Azalia) is a specification for the audio sub-system of personal computers. It was released by Intel in 2004 as the successor to their AC'97 PC audio standard. Featur ...

(HD Audio) which is a successor that is not

backward compatible Backward compatibility (sometimes known as backwards compatibility) is a property of an operating system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially in ...

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 ( 7.1 surround sound).

Revisions

AC'97 has had several revisions: * AC'97 1.x compliant indicates fixed 48 kHz 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 Sony/Philips Digital Interface Format * AC'97 2.3 compliant indicates extended configuration information and optional jack sensing support AC'97 revision 2.3 enables

Plug and Play In computing, a plug and play (PnP) device or computer bus is one with a specification that facilitates the recognition of a hardware component in a system without the need for physical device configuration or user intervention in resolving resou ...

for the end user. This revision provides means for the audio codec to supply parametric data about its analog interface much like

AC-Link

The AC-Link is a digital link that connects the DC97 (the controller) 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 (12.288 Mbit/s) between the controller and one or more 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 scheme. Every frame is subdivided in 13 slots. The first (slot 0) is 16 bits long and contains validity flags for the remaining slots, while the remaining 240 bits are divided in twelve 20-bit slots (slots 1–12), 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 Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM Stream (comp ...

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 (such as 44.1 kHz) are implemented using a handshake protocol between the controller and codec which skips data during certain frames. (This capability depends on the codec. Alternatively,

sample rate conversion Sample-rate conversion, sampling-frequency conversion or resampling is the process of changing the sampling rate or sampling frequency of a discrete signal to obtain a new discrete representation of the underlying continuous signal. Application ...

could be performed in the DC97 (controller) or in the software driver.)

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 (48-pin

QFP A quad flat package (QFP) is a surface-mounted integrated circuit package with "gull wing" leads extending from each of the four sides. Socketing such packages is rare and through-hole mounting is not possible. Versions ranging from 32 to 304 ...

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) The AKM () is an assault rifle designed by Soviet small arms designer Mikhail Kalashnikov in 1959. It is the most ubiquitous rifle of the Kalashnikov rifles. It was developed as a replacement to the AK-47 introduced a decade prior. Introduced ...

AK 4540, 4543, 4544A, 4545 *

Avance Logic Realtek Semiconductor Corp () is a fabless semiconductor company situated in the Hsinchu Science Park, Hsinchu, Taiwan. Realtek was founded in October 1987 and subsequently listed on the Taiwan Stock Exchange in 1998. Realtek currently manufactu ...

(now Realtek) ALC201A, ALC202/A, ALC650, ALC655, ALC658, ALC101, ALC202A, ALC250, ALC850, ALC888 *

Conexant Conexant Systems, Inc. was an American-based software developer and fabless semiconductor company that developed technology for voice and audio processing, imaging and modems. The company began as a division of Rockwell International, before ...

Cx20468 - with a modem * Cirrus Logic CrystalWare 4236, CrystalClear SoundFusion CS4297, CS4299 *

Crystal Semiconductor Cirrus Logic Inc. is an American fabless semiconductor supplier that specializes in analog, mixed-signal, and audio DSP integrated circuits (ICs). Since 1998, the company's headquarters have been in Austin, Texas. The company's audio process ...

s CS4205, CS4202 *

C-Media C-Media Electronics, Inc. () is a Taiwan computer hardware company that manufactures processors for PC audio and USB storage, and wireless audio devices. Products ISA audio * CMI8328 * CMI8330 PCI audio * CMI8338 * CMI8738-SX * CMI87 ...

CMI9738, 9739, 9761, 9880 *

ESS The suffix ''-ess'' (plural ''-esses'') appended to English words makes a female form of the word. ESS or ess may refer to: Education * Ernestown Secondary School, in Odessa, Ontario * European Standard School, in Dhaka, Bangladesh Governmen ...

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 Intersil is an American semiconductor company headquartered in Milpitas, California. As of February 24, 2017, Intersil is a subsidiary of Renesas. The previous Intersil was formed in August 1999 through the acquisition of the semiconductor busin ...

HMP9701 (obsolete, 48 kHz fixed samplerate) *

National Semiconductor National Semiconductor was an American semiconductor manufacturer which specialized in analog devices and subsystems, formerly with headquarters in Santa Clara, California. The company produced power management integrated circuits, display dr ...

LM4550, LM49321, LM49350, LM49352 *

Philips Koninklijke Philips N.V. (), commonly shortened to Philips, is a Dutch multinational conglomerate corporation that was founded in Eindhoven in 1891. Since 1997, it has been mostly headquartered in Amsterdam, though the Benelux headquarters i ...

UCB 1400 (with touchscreen controller) * Realtek ALC5610 ALC5611 * SigmaTel (now IDT) C-Major STAC 9460 (D/A only), 9461, 9462, 9463, 9200, 9202, 9250, 9251, 9220, 9221, 9223, 9750 *

Silicon Image Silicon Image is a provider of semiconductors for the mobile, consumer electronics and personal computers (PCs). It also manufactures wireless and wired connectivity products used for high-definition content. The company’s semiconductor and IP ...

Si3024 (mono only) * TriTech Microelectronics TR28022, 28026 *

Yamaha Yamaha may refer to: * Yamaha Corporation, a Japanese company with a wide range of products and services, established in 1887. The company is the largest shareholder of Yamaha Motor Company (below). ** Yamaha Music Foundation, an organization estab ...

YMF 743, 752, 753 * VIA VT1612, VT1616 (VIA Six-TRAC Vinyl Audio) * 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 with standard color jack. Intel provides a specification for that header; the signal assignments are different for AC'97 and

br>headers

Operating system support

AC'97 is supported by most operating systems, such as Windows (starting with

Windows 98 Windows 98 is a consumer-oriented operating system developed by Microsoft as part of its Windows 9x family of Microsoft Windows operating systems. The second operating system in the 9x line, it is the successor to Windows 95, and was released to ...

) and Linux. Under DOS, applications access the sound hardware directly instead of through the operating system, and most DOS applications do not support AC'97. 64-bit versions of Windows 7 and later require a third-party driver for AC'97 support.

References