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Principles of Digital Audio
Principles of Digital Audio, by Ken C. Pohlmann (McGraw-Hill Professional), starting at $0.19


Home » Other » Audio
What is High Definition Audio
Author: Gabriel Torres 170,206 views
Type: Tutorials Last Updated: December 22, 2005
Page: 1 of 1

High Definition Audio, also known as HD Audio or by its codename, Azalia, is an audio standard created by Intel to be used on their chipsets, i.e., it is a standard for high-quality on-board audio. In this tutorial we will explain more about this feature.

All Intel chipsets based on PCI Express bus – like i915 and i925 – support High Definition Audio. This standard provides two new features: multi-streaming, which allows more than one audio signal to be sent to a different audio device – for example, to watch a DVD on your living room transferring the audio through a wireless network while talking through a voice over IP solution at the same time on your desktop in your office – and high quality audio.

Before HD Audio was released, on-board high quality audio was only available if your motherboard had a separated high quality audio controller – like Envy24 from VIA, for example. With HD Audio technology, the south bridge of the chipset produces high-quality audio itself, without the need of a separated controller chip, what would make the motherboard more expensive. The south bridge only needs an external codec (coder/decoder) chip to make the needed digital/analog and analog/digital conversions. This kind of chip is inexpensive compared to a ”full“ controller chip. One example of codec compatible with Intel’s HD Audio is C-Media 9880.

High Definition Audio provides 7.1 surround audio with 192 kHz sampling rate and up to 32-bit resolution. Other audio solutions embedded on the chipset support a maximum of 48 kHz sampling rate and 20-bit resolution, even when they support 5.1 configuration (”6-channel surround audio“).

Intel is promoting High Defition Audio together with Dolby Laboratories, who created three audio ”levels“ for PCs using HD Audio: Dolby Sound Room, Dolby Home Theater and Dolby Master Studio, which are targeted to the entry-level user, to the mid-range user and to the high-end user, respectively. The features of these ”levels“ are the following:

  • Dolby Sound Room: 2-channel audio supporting Dolby Virtual Speaker and Dolby Head Phones technologies. These two technologies simulate 5.1 audio using only 2 speakers, based on Dolby Pro Logic II technology. It has a signal-to-noise ratio of at least 75 dB.
  • Dolby Home Theater: 6-channel (5.1) audio with a signal-to-noise ratio of at least 85 dB, based on Dolby Pro Logic II technology.
  • Dolby Master Studio: 8-channel (7.1) audio with a signal-to-noise ratio of at leas 95 dB, based on Dolby Pro Logic IIx and Dolby Digital Live technologies.

Something really interesting about Dolby Pro Logic II technology it that it allows the system to use 5.1 audio (or 7.1 audio with Dolby Pro Logic IIx) even if the audio source has only two channels (as it happens with CDs, for example), through the use of a series of filters.

Digital Live technology is the streaming technology from Dolby Labs, used to transfer music that is stored in the PC to a receiver located in your living room through wireless LAN, for example.

The idea behind these ”levels“ is to make it easy for the user to know what is the on-board audio quality from the motherboard he (or she) is buying, simply paying attention to what Dolby logo is printed on the box (Sound Room, Home Theater or Master Studio).

We’ve listened to some demos and we were really impressed by Dolby Pro Logic IIx technology, which separates CD audio (which only has 2 channels) into eight channels (7.1 format). The result is really impressive, it look like if the CD was originally recorded using 7.1 audio.

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