AC'97 (abbreviated from English Audio Codec '97 ) is a standard for audio codecs developed by Intel Architecture Labs of Intel in 1997. [1] This standard is used in motherboards, modems, sound cards and supports a sampling frequency of 96 kHz at using 20-bit stereo and 48 kHz when using 20-bit stereo for multi-channel recording and playback.
AC'97 consists of a host controller chipset integrated into the south bridge and an audio codec located on the board. The host controller (aka digital controller, DC'97; Eng. Digit controller) is responsible for the exchange of digital data between the system bus and the analog codec. An analog codec is a small chip (4 × 4 mm, TSOP housing, 48 pins) that performs analog-to-digital ( ADC ) and digital-to-analog ( DAC ) conversions in program transmission mode or via DMA . It consists of a node that directly performs the conversion - ADC / DAC. The quality of the digitization and decoding of digital sound largely depends on the quality of the used ADC / DAC.
Subsequently, in 2004, Intel released the specification HD Audio ( High Definition Audio , high definition sound), although it is the successor of the AC'97 specification, but does not provide backward compatibility with it [2] . HD Audio provides more channels with higher sound quality than with the integrated AC'97 audio codecs. Hardware based on HD Audio supports 8-, 16-, 20-, 24- and 32-bit samples with a sampling frequency of up to 192 kHz in stereo and up to 96 kHz in multi-channel modes. The number of channels can reach 16. Codecs AC'97 and HD Audio are not interchangeable, their information transfer protocols are not compatible.
Riser Cards
The I / O Controller Hub included a digital controller that met AC'97 specifications. This controller allowed the use of software and sound modem codecs (no more than two devices in total). Devices connect to other components of the computer and to the controller itself using the high-speed serial bi-directional digital bus AC - Link. The AC - Link interface allows you to work with 12 input and output data streams with a bit capacity of 20 bits and a sampling frequency of 48 kHz.
Thus, manufacturers of motherboards could install a sound or modem DAC / ADC on their boards, and get a sound card or modem (almost completely software) for free. With sound cards, everything is quite simple - the speakers of different manufacturers are basically the same and have the same connector for connecting to a sound card, so many motherboards already have an integrated sound card that works through the AC'97 controller. But with modems a little differently. Standards for telephone lines in different countries may vary significantly. Therefore, on the motherboards there is a 46-pin AMR slot, resembling in appearance a half-shortened PCI slot, which is essentially an AC-Link bus connector. Devices that comply with the AC - Link specification can be installed in the AMR slot (this can be either a modem or a combined audio / modem riser card). A riser card is a card assembled using the above technology (for example, an AMR modem card)
Notes
- ↑ World of PC magazine 12/2013, p. 24
- ↑ High Definition Audio Specification Revision 1.0a . Intel Corporation (2010).