Intel High Definition Audio
Intel High Definition Audio (also called HD Audio or Azalia) refers to the specification released by Intel in 2004[1] for delivering high-definition audio that is capable of playing back more channels at higher quality than previous integrated audio codecs like AC'97. During development it had the codename Azalia.
Hardware based on Intel HD Audio specifications is capable of delivering 192-kHz 32-bit quality for two channels, and 96-kHz 32-bit for up to eight channels.[citation needed] However, as of 2008[update], most audio hardware manufacturers do not implement the full high-end specification, especially 32-bit sampling resolution (though this would be pointless anyway, as no electronics are capable of reproducing anything above 22 bits, nor are humans capable of perceiving it).
Microsoft Windows XP SP3 and later Windows versions[2] include a Universal Audio Architecture (UAA) class driver which supports audio devices built to the HD Audio specification. There are UAA drivers for Windows 2000 and Windows XP SP2 as well. Mac OS X has full support with its AppleHDA driver. Linux also supports Intel HDA controllers, as do the OpenSolaris,[3] FreeBSD,[4] NetBSD and OpenBSD[5] operating systems.
Like AC'97, HD Audio is a specification that defines the architecture, link frame format, and programming interfaces used by the controller on the PCI bus and by the codec on the other side of the link. Implementations of the host controller are available from at least Intel, Nvidia, and AMD.[6] Codecs which can be used with such controllers are available from many companies, including Realtek,[7] Conexant, Analog Devices (SoundMAX),[8] Integrated Device Technology (IDT) (acquired from SigmaTel), VIA, Wolfson Microelectronics, and formerly C-Media.
[edit] 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, but the signal assignments are different for AC'97 and HD Audio headers.[9]
The HDA 3.5 mm connectors are different from connectors used in AC'97 specification and general audio equipment. A regular 3.5 mm jack typically has one pin for ground, two pins for stereo signal and two pins for return signal.
In the AC'97 design, the audio output is sent to the jack. If the headphones are not plugged in, the jack directs the audio to the return pins that are connected to the speakers. When a headphone is plugged into the front panel jack, the audio signal goes to the headphones; the return pins are disconnected, so no audio signal goes to the speakers.
With HD Audio, instead of the return signal pins, there is a sense signal that is connected to an isolated switch inside the headphone jack that detects when the headphone plug is inserted. When the plug is inserted, the isolated switch informs the motherboard, and the codec sends audio to the headphones. When the plug is not inserted, the codec sends the audio directly to the speakers (the audio does not go out to the front panel and then loop back to the speakers). A similar isolated switch is used to detect when a microphone has been plugged in.
The different signal assignments can cause trouble when AC'97 front panel dongles are used with HDA motherboards and vice versa. A loud audio passage may make the HDA motherboard with AC'97 dongle believe that headphones and microphones being plugged and unplugged hundreds of times per second. An AC'97 motherboard with an HDA dongle will route the 5 V audio supply (silence) to the speakers instead of the desired audio.
[edit] References
- ^ High Definition Audio Specification, Revision 1.0a, 2010
- ^ Microsoft Knowledge Base Article 888111
- ^ OpenSolaris Boomer Project Page, 2009
- ^ http://man.freebsd.org/snd_hda
- ^ http://www.openbsd.org/cgi-bin/man.cgi?query=azalia
- ^ AMD SB600 Product Information Page, 2009
- ^ ALC888 Product Page, 2009
- ^ AD1988 Product Information Page, 2009
- ^ Intel Corporation (February 2005), Front Panel I/O Connectivity Design Guide, Version 1.3, pp. 19–25, http://www.formfactors.org/developer/specs/A2928604-005.pdf
[edit] External links
- Intel High Definition Audio
- High Definition Audio Specification 1.0a (June 17, 2010)
- Motherboard/Sound-cards connectors pinout specifications
- Developer Education Resource: High Definition Audio for the Digital Home
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