AC97
Encyclopedia
AC'97 is Intel Corporation
's Audio Codec
standard developed by the Intel Architecture Labs
in 1997, and used mainly in motherboard
s, modem
s, and sound card
s.
Audio components integrated into chipset
s consist 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. 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, whereas HD Audio has the capability to define many more channels but in practice most motherboards only allow for up to 8 channels.
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In 2004 AC'97 was superseded by Intel High Definition Audio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).
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
.
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.
headers.
Intel Corporation
Intel Corporation is an American multinational semiconductor chip maker corporation headquartered in Santa Clara, California, United States and the world's largest semiconductor chip maker, based on revenue. It is the inventor of the x86 series of microprocessors, the processors found in most...
's Audio Codec
Codec
A codec is a device or computer program capable of encoding or decoding a digital data stream or signal. The word codec is a portmanteau of "compressor-decompressor" or, more commonly, "coder-decoder"...
standard developed by the Intel Architecture Labs
Intel Architecture Labs
Intel Architecture Labs, also known as IAL, was the personal computer system research and development arm of Intel Corporation during the 1990s...
in 1997, and used mainly in motherboard
Motherboard
In personal computers, a motherboard is the central printed circuit board in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple...
s, modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
s, and sound card
Sound card
A sound card is an internal computer expansion card that facilitates the input and output of audio signals to and from a computer under control of computer programs. The term sound card is also applied to external audio interfaces that use software to generate sound, as opposed to using hardware...
s.
Audio components integrated into chipset
Chipset
A chipset, PC chipset, or chip set refers to a group of integrated circuits, or chips, that are designed to work together. They are usually marketed as a single product.- Computers :...
s consist of two components: an AC'97 digital controller (DC97), which is built into the I/O Controller Hub
Southbridge (computing)
The southbridge is one of the two chips in the core logic chipset on a personal computer motherboard, the other being the northbridge. The southbridge typically implements the slower capabilities of the motherboard in a northbridge/southbridge chipset computer architecture. In Intel chipset...
(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
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
audio architecture with surround sound
Surround sound
Surround sound encompasses a range of techniques such as for enriching the sound reproduction quality of an audio source with audio channels reproduced via additional, discrete speakers. Surround sound is characterized by a listener location or sweet spot where the audio effects work best, and...
support for the PC. AC'97 supports a 96 kHz sampling rate
Sampling rate
The sampling rate, sample rate, or sampling frequency defines the number of samples per unit of time taken from a continuous signal to make a discrete signal. For time-domain signals, the unit for sampling rate is hertz , sometimes noted as Sa/s...
at 20-bit stereo resolution
Audio bit depth
In digital audio, bit depth describes the number of bits of information recorded for each sample. Bit depth directly corresponds to the resolution of each sample in a set of digital audio data...
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, whereas HD Audio has the capability to define many more channels but in practice most motherboards only allow for up to 8 channels.
Integrated audio is implemented with the AC'97 Codec on the motherboard
Motherboard
In personal computers, a motherboard is the central printed circuit board in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple...
, a Communications and Networking Riser
Communications and Networking Riser
Communications and Networking Riser 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 any combination on a CNR card...
(CNR) card, or an audio/modem riser
Audio/modem riser
The audio/modem riser, also known as an AMR slot, is a riser expansion slot found on the motherboards of some Pentium III, Pentium 4, Duron, and Athlon personal computers...
(AMR) card.
In 2004 AC'97 was superseded by Intel High Definition Audio
Intel High Definition Audio
Intel High Definition Audio refers to the specification released by Intel in 2004 for delivering high-definition audio that is capable of playing back more channels at higher quality than previous integrated audio codecs like AC'97...
(HD Audio).
Revisions
AC'97 has had several revision:- 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
Analog device
Analog device is an apparatus that measures continuous information. The measured analog signal has an infinite number of possible values. The only limitation on resolution is the accuracy of the measuring device. Such apparatus operates with variables which are constituted by continuously measured...
much like Intel High Definition Audio
Intel High Definition Audio
Intel High Definition Audio refers to the specification released by Intel in 2004 for delivering high-definition audio that is capable of playing back more channels at higher quality than previous integrated audio codecs like AC'97...
.
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
Time-division multiplexing
Time-division multiplexing is a type of digital multiplexing in which two or more bit streams or signals are transferred apparently simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel. The time domain is divided into several recurrent...
) 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
Sample rate conversion
Sample rate conversion is the process of converting a signal from one sampling rate to another, while changing the information carried by the signal as little as possible...
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 DevicesAnalog DevicesAnalog Devices, Inc. , known as ADI, is an American multinational semiconductor company specializing in data conversion and signal conditioning technology, headquartered in Norwood, Massachusetts...
AD1819B, 1881A, 1885, 1886, 1887, 1980, 1981, 1985 - AKM (Asahi Kasei Microsystems) AK 4540, 4543, 4544A, 4545
- Avance Logic (now RealtekRealtekRealtek Semiconductor Corp. , a fabless IC design house situated in the Hsinchu Science Park, Hsinchu, Taiwan, was founded in October 1987, and subsequently approved as a listed company on the Taiwan Stock Exchange in 1998...
) ALC201A, ALC202/A, ALC650, ALC655, ALC658, ALC101, ALC202A, ALC250, ALC850, ALC888 - ConexantConexantConexant Systems, Inc. is an American semiconductor company, formerly the semiconductor division of Rockwell International. Currently it's privately owned by Golden Gate Capital, an equity firm headquartered in San Francisco.-History:...
Cx20468 - with a modem - Cirrus LogicCirrus LogicCirrus Logic is a fabless semiconductor supplier specializing in analog, mixed-signal, and audio DSP integrated circuits . They are presently headquartered in Austin, Texas. Their audio processors and audio converters are found in many professional audio and consumer entertainment products,...
CrystalWare 4236, CrystalClear SoundFusion CS4297, CS4299 - Crystal Semiconductors CS4205, CS4202
- C-MediaC-MediaC-Media Electronics, Inc. is a Taiwanese computer hardware company that manufactures processors for PC audio and USB storage, and wireless audio devices.-Products:-PCI audio:*CMI8338*CMI8738-SX*CMI8738-LX*CMI8738-MX*CMI8768...
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)
- IntersilIntersilIntersil Corporation is an American company that specializes in the design, development and manufacturing of high-performance analog semiconductors for four high-growth markets — Communications, Computing, High End Consumer and Industrial.-Company history:...
HMP9701 (obsolete, 48 kHz fixed samplerate) - National SemiconductorNational SemiconductorNational Semiconductor was an American semiconductor manufacturer, that specialized in analog devices and subsystems,formerly headquartered in Santa Clara, California, USA. The products of National Semiconductor included power management circuits, display drivers, audio and operational amplifiers,...
LM4550, LM49321, LM49350, LM49352 - PhilipsPhilipsKoninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....
UCB 1400 (with touchscreen controller) - RealtekRealtekRealtek Semiconductor Corp. , a fabless IC design house situated in the Hsinchu Science Park, Hsinchu, Taiwan, was founded in October 1987, and subsequently approved as a listed company on the Taiwan Stock Exchange in 1998...
ALC260, ALC658, ALC655 (16-bit), ALC650, ALC268, ALC888 - SigmaTelSigmaTelSigmaTel is an electronics company located in Austin, TX, which designs mixed audio signal processors, and controller chips for multifunction peripherals. SigmaTel was Austin's largest IPO as of 2003 when it became publicly traded on NASDAQ...
(now IDTIntegrated Device TechnologyIntegrated Device Technology, Inc. is a publicly traded corporation headquartered in San Jose, California, that designs, manufactures, and markets low-power, high-performance mixed-signal semiconductor solutions for the advanced communications, computing, and consumer industries. The company...
) 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
- VIAVIA TechnologiesVIA Technologies is a Taiwanese manufacturer of integrated circuits, mainly motherboard chipsets, CPUs, and memory, and is part of the Formosa Plastics Group. It is the world's largest independent manufacturer of motherboard chipsets...
VT1612, VT1616 (VIA Six-TRAC Vinyl Audio), VT82C686 - WinbondWinbondWinbond Electronics Corporation is a Taiwan-based corporation founded in 1987 that produces semiconductors and several types of integrated circuits, most notably Dynamic RAM, Static RAM, microcontrollers, and personal computer ICs...
W83971 - Wolfson MicroelectronicsWolfson MicroelectronicsWolfson Microelectronics plc is a multinational microelectronics and fabless semiconductor company headquartered in Edinburgh, United Kingdom. It specialises in signal processing chips for the consumer electronics market and has engineering and sales offices throughout Asia-Pacific, Europe and the...
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 AudioIntel High Definition Audio
Intel High Definition Audio refers to the specification released by Intel in 2004 for delivering high-definition audio that is capable of playing back more channels at higher quality than previous integrated audio codecs like AC'97...
headers.
See also
- I²SI²SI2S, also known as Inter-IC Sound, Integrated Interchip Sound, or IIS, is an electrical serial bus interface standard used for connecting digital audio devices together. It is most commonly used to carry PCM information between the CD transport and the DAC in a CD player...
(Integrated Interchip Sound) - Audio/modem riserAudio/modem riserThe audio/modem riser, also known as an AMR slot, is a riser expansion slot found on the motherboards of some Pentium III, Pentium 4, Duron, and Athlon personal computers...
(AMR) - Advanced Communications RiserAdvanced Communications RiserThe Advanced Communications Riser, or ACR, is a form factor and technical specification for PC motherboard expansion slots. It is meant as a supplement to PCI slots, a replacement for Audio/modem riser slots, and a competitor and alternative to Communications and Networking Riser ...
(ACR) - Communications and Networking RiserCommunications and Networking RiserCommunications and Networking Riser 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 any combination on a CNR card...
(CNR) - S/PDIFS/PDIFS/PDIF is a digital audio interconnect used in consumer audio equipment over relatively short distances. The signal is transmitted over either a coaxial cable with RCA connectors or a fiber optic cable with TOSLINK connectors. S/PDIF interconnects components in home theaters and other digital high...
Sony/Philips Digital Interface Format