What is HD Audio

HD Audio is High Definition Audio, meaning high-fidelity audio.
As the IT industry's first widely specification, AC'97 in the face of the new DVD-Audio, SACD multi-channel high quality music encoding a bit old, although the three big upgrade but still appears to heart more than the weak.
In order to change this situation, April 15, 2004, Intel and other global companies a more than 80 developed a new standard, code-named Azalia, standards were introduced shortly after the renamed HD Audio.
HD Audio with high flexibility, mobility, low cost, high stability characteristics, and allow ample space for the upgrade, all will be able to make it spread rapidly.
Contrast AC'97 HD Audio

1 sample size
AC'97 in early calendar after three major changes, AC'97 1.x for a fixed 48kHz (hertz) sampling output; AC'97 2.1: expanded part of the audio features, began to support a variety of sampling rates and multi-output sound channel output; AC'97 2.2: a more complete and extended some of the audio features, began to support S / PDIF output.
S / PDIF is Sony / Philips Digital Interface, Sony Philips digital interface.
AC'97 AC'97 2.3 is the latest version, support the expansion of audio technology, multi-sampling rate (8,11.025,16,22.05,32,44.1 and 48kHz) and multi-channel, enhanced upgrade support, optional S / P DIF digital interface, extended configuration information.
A dedicated stereo output (Line Out), an additional stereo output (Aux Out) can be configured as line output, optional headphone output, optional 4 or 6 channel output.
Optional 18Bit or 20Bit DAC and ADC, optional pitch and loudness control, 3D stereo output enhancement.
Even the final version, AC'97 specifications are far less than the HD Audio, in order to maximize access to "real fine" sound, HD Audio audio processing specification to the 32bit/192kHz.
This includes two concepts, the former is the sampling precision, the more bits, the amount of data available to describe the sound more rich; which represents the sampling frequency, the higher the frequency, the shorter the time interval, the received voice the more delicate and smooth.
In the actual output, HD Audio can also be reached 24bit/192kHz, this level in the specification has been with the use of DSD technology SACD player match.
In contrast, the present CD-Audio technology specifications 16bit/44.1kHz, DVD-Audio standard only 24bit/96kHz.
Clearly, HD Audio high targets in the sampling area it can be easily done DVD-Audio, DVD-Video, CD-Audio audio playback.
Intel originally intended to also support HD Audio SACD audio standard, but on the PC DVD-ROM not physically support SACD discs, and functions to achieve DSD encoding / decoding chip costly, Intel eventually gave up this practice, Perhaps only until the time is ripe (for example, after the popularity of Blu-ray DVD) HD Audio will be in future releases.
(2) to solve the problem SRC
Not only the SRC into the AC'97 integrated audio, but also into the design in accordance with this specification in a separate sound card.
The SRC HD Audio is most concerned about some of the players, we collect data, most of the information or did not elaborate, or vague, some of it is not mentioned.
In fact HD Audio specification issues have been resolved SRC, or by driving, the problem can be completely bypass the SRC.
Past, because all non-final version of the AC'97 specification versions are fixed 48kHz output, so ordinary 44.1kHz audio sample size (such as CD), or jitter must be achieved by shifting upward to 44.1 48kHz output specifications.
As a result there will be loss of sound quality.
Intel's official website we do not have to get more information and instead set his sights on the largest supplier of motherboard integrated audio chip Realtek body.
From the Realtek chip data, we see the characteristics of the chip specifications.
SRC in order to solve the problem, ALC888S can provide two kinds of 44.1 kHz and 48 kHz sampling size, frequency, and multiplying by the more expanded frequency support.
In other words, 44.1 kHz or even hit 48 kHz, or more of the other norms of the sampling rate, without the need for conversion, the original sampling rate can be converted to analog output directly.
3 data channels
ICH6 is the first direct support for HD Audio South Bridge chips, we have introduced to the platform, for example HD Audio package of hardware architecture.
Can be seen from the figure, HD Audio CODEC chip solutions in the key part of it through a special "Azalia Link" bus and control logic connected to the ICH6, and this Azalia Link provides up to 48Mbps and 24Mbps bandwidth, single-output single- input bandwidth, hardware manufacturers can expand as needed for the multiple connections to achieve higher bandwidth!
The AC'97 CODEC is the standard by "AC-Link" bus connected with the control logic, the bus can only provide a mere 11.5Mbps the total bandwidth, significantly less than HD Audio system.
The role of the high interface bandwidth can enter more data, and this truly is the HD Audio high sampling accuracy, a prerequisite for multi-channel output.
In addition, HD Audio also introduced dynamic bandwidth allocation mechanisms to improve bandwidth utilization, high-precision audio streams can occupy more of the bus resources, and low accuracy of audio data is less, thus providing near-perfect listening experience This is significantly better than the AC'97 fixed allocation mechanism.
4 more audio playback system:
In addition to the sampling rate called luxury and playback accuracy outside, HD Audio playback and multi-input audio stream is equally outstanding.
HD Audio audio interface, the interface with the so-called routing and auto-recognition feature, an HD Audio audio system using a PC can simultaneously output four unrelated audio with each other without disturbing each other, thus allowing simultaneous PC different audio applications.
For example, through the audio cable / wireless network connection the living room speakers; the same time by connecting the HD Audio sound card playback of multimedia speakers on the game's music effects; followed with a PC headset to listen to the playback of MP3 music ... if want to through the microphone on the remote network of friends with the exchange, HD Audio can handle it.
These applications can be at the same time, the user just like with multiple independent audio equipment, while a number of audio-related processing will no longer be a problem.
5 more audio support
High-end sound card has its own sound technologies, such as Creative EAX series and proud sharp A3D, these audio technologies are actually a collection of the library, these functions provide specific computing model, by computing simulation of space-sense three-dimensional sound field effect, users get an excellent sense of hearing experience.
For example, use good quality headphones to listen to sound card output to the rain, if the sound card's audio technology good enough to make the listener think that the rain will not come from the headphones, but really it was raining outside.
This situation may appear only in the high-end audio systems, cheap AC'97 expect to achieve this effect naturally unrealistic.
Therefore, Intel HD Audio as the audio technology of points, in cooperation with Dolby HD Audio integrated advanced audio features, which enhance the PC audio experience (Dolby regard, we dealt with separately).
6 hardware support for Dolby audio technology
AC'97 soft sound card in the sound has always been a lack of capacity, CODEC itself does not support extra audio technology, but only through software support, relying on CPU power-AC '97 soft sound bad reputation to a large extent from here.
HD Audio Intel determined to get out of this situation, for which it worked closely with Dolby Laboratories, for HD Audio can be implemented in hardware Dolby Headphone, Dolby Virtual Speaker, Dolby ProLogic Ⅱ, Dolby ProLogic Ⅱ x and Dolby Digital Live feature.
Thus, in line with standard HD Audio CODEC chip will have a certain sound processing capabilities.
Of course, the specific encoding and decoding operations still have to be completed by the CPU, CODEC is to provide an input / output interface only, so that will not cause any burden CODEC chip, technically easy to implement.
The only drawback: HD Audio features advanced audio may cause some of the burden of the CPU, but it is clearly beneficial to the CPU vendors harmless: HD Audio high-end CPU might be able to effectively stimulate consumer demand, a PC industry growth another driving force.
7 more user-friendly audio interface
In order to chassis front panel audio connector to play a role, we must use the front panel audio signal wiring and HD Audio CODEC provides specialized pins connected - from the physical point of view, HD Audio and AC'97 CODEC audio pin there is no difference, but there are several pin definition has changed, from which we can see, the connection pins 1,3,5,9 pin is for audio input / output connections, 6, 10-pin is used to return to automatic detection results, so that the front panel HD Audio also achieved a "plug and play" function, users connect speakers, headphones, microphone-like device is very convenient.
Conclusion
From the normative influence on the industry to see, HD Audio is less than AC'97, but from our analysis point of view, HD Audio advantage is quite obvious.
If further influence extended to a wider area, I believe that is the industry's progress can be expected, after all, in the specification, HD Audio has a more obvious advantage, and this also reflects the norms of development potential.
On the other hand, from our previous application and test scores to see, even the most high-end integrated sound card, RAMM test results are not particularly desirable; therefore, hopes to reach a certain HD Audio onboard sound card independent of the price performance of quality ideas may come to nothing.
And from a hardware perspective, there is no I / O control and DSP hardware, soft sound in performance with an independent sound card is not yet match.
If the future appears even higher bit rate audio specifications, integrated sound card might be a bottleneck here.
If you have high requirements for audio, then our proposal is still to buy separate sound card.