http://en.wikipedia.org/wiki/AC97AC97From Wikipedia, the free encyclopediaAC'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. AC '97 v2.3[1] enables Plug and Play audio for the end user. This version provides parametric data about the analog device being used. In 2004 AC'97 was superseded by Intel High Definition Audio (HD Audio).
[edit] AC-LinkThe 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. [edit] Problems
The AC97 is shipped for Microsoft operating systems (Windows XP and Vista) with an audio settings program[2]. Various versions of this program exist, for configuring the audio settings including the input and output connector configuration, sound effects, an equalizer "mixer board", 3D sound configuration, and microphone echo cancellation[3]. Many people are not aware of this program[4], and once pointed to this program, find that an unwanted sound effect was inadvertently set to be active.[5]
Most of the AC97 on-board sound card versions are typically shipped with three RCU connectors marked in three colors: pink, green and blue, according to PC99 Color-coding scheme. The pink connector is meant for a microphone, the green either for line-out to amplified speakers, or to a line-in wire, and the blue has an amplified signal for un-amplified or slightly amplified headphones. The audio settings program has a problem when set to Headphones or to Stereo Speakers, and will only work when configured to be set as a multi-speaker unit with 3 speakers or more. The speakers actually attached to one of the outputs (and only one output typically works), are behaving as background speakers for 3D sound effect, and for this reason will play only music and not talking, or will work only with a sound effect set on, and no sound will be heard when the sound effect is set to NONE. In many cases no solution has been found for this problem, and most technical advice sites advise to simply buy a low-cost external soundcard.[6]
Microsoft has acknowledged that in one of their automatic updates they have caused the AC97 to stop working[7]. This has been corrected in a subsequent version of updates, and is now treated as missing the updated driver.[8] [edit] Codec chipsCodec 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.
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