thumb|Realtek ALC 882 HD Audio Codec

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, but it is not backwards-compatible with it.

Features

The Intel High Definition Audio specification includes the following features:

  • Up to 15 input and 15 output streams
  • Up to 16 PCM audio channels per stream
  • Sample resolutions of 8, 16, 20, 24 and 32 bits
  • Sample rates of 6–192 kHz, and with vendor drivers, up to 384 kHz is possible
  • Support for audio codecs (e.g., ADC, DAC, DSP), modem codecs, and vendor-offered codecs
  • Discoverable codec architecture
  • Fine-grained codec power-control
  • Audio jack detection, sensing, and retasking
  • Support for digital audio output, such as HDMI and S/PDIF, and the actual DAC operations are happen on digital audio devices such as HDMI-based TVs and monitors
  • Vendor-offered (OEM or IHV) audio enhancement features

Motherboards typically do not have any more than eight built-in output channels (7.1 surround sound) and four input channels (back and front panel microphone inputs, and a back-panel stereo line-in). Users requiring more audio I/Os will typically opt for a sound card or an external audio interface, as these provide additional features that are more oriented towards professional audio applications.

Operating system support

The Service Pack 3 update to Windows XP and all later versions of Windows (from Vista onwards) included the Universal Audio Architecture (UAA) class driver, which supported audio devices built to HD Audio's specifications. Retrospective UAA drivers were also built for Windows 2000, Server 2003 and XP Service Pack 1/2. macOS provides support for Intel HD Audio with its AppleHDA driver. Several Linux operating systems also support HD Audio, as well as OpenSolaris, FreeBSD, and OpenBSD. In Microsoft Windows, vendor-offered audio enhancement features usually required vendor drivers.

Host controller

Like AC'97, HD Audio acts as a device driver, defining the architecture, link frame format, and programming interfaces used in the hardware of the host controller of the PCI bus and linking it to a codec used by a computer's software. Configurations of the host controller (Chipset) are available from third-party suppliers, including Nvidia, VIA and AMD, AMD's TRX40 chipset was introduced in 2019 for use with Ryzen "Threadripper" CPUs, which provided no HD Audio interface. As a result, a separate USB audio interface converter, USB codec, or PCIe audio device was required to integrate audio on TRX40 motherboards. This was a temporary measure until a new Audio bus was developed by AMD named Audio CoProcessor (ACPBus). Intel has also decoupled the audio controller from its chipsets in favor of Intel Smart Sound Technology (SST) or I²S instead of the more traditional HD Audio Bus. A HD Audio controller can include vendor-offered audio enhancement features known as Audio Processing Objects (APOs), offered by companies like Dolby, Creative, Fortemedia, Nahimic, Poly Inc, DTS and Waves Audio, they can be software-based and driver-based. The HD Audio codec itself, especially Realtek brand, may also include APOs for audio enhancement features.

Limitations

As with the previous AC'97 standard, HD Audio does not specify handlers for the media buttons attached to headphone jacks (i.e., Play/Pause, Next, Previous, Volume up, Volume down).

Front panel connector

Computer motherboards often provide a connector to bring microphone and headphone signals to the computer's front panel. Intel provides a general specification for this process, but the signal assignments are different for both AC'97 and HD Audio headers.

The pin assignments for the AC'97 and HD Audio connectors are: