Articles: Multimedia

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Our first review of existing integrated audio solutions had a great feedback (I guess my colleagues who review mainboards should pay more attention to their audio subsystems :). I would like to express my appreciation to all readers who took pains of emailing me their responses and suggestions. Some topics I am going to discuss in this article have been included only thanks to your feedback.

And the topics of our today’s discussion are:

  • Difference between AC’97 specification editions and a thorough examination of the new Jack Sensing technology. We will see how it works in a codec from Analog Devices;
  • VIA’s attempts to bring eight-channel sound to mainboards with the company’s new version of their audio-controller (Envy24PT) and their own codec (VT1616);
  • Realtek’s family of six-channel codecs, with description of the newest software version.

From Microsoft Labs: Plug & Play for Analog Audio Devices

Every brilliant idea must be simple in the first hand! They must have posted this slogan on the wall of the Microsoft lab for the engineers to realize that their problem had a much simpler solution than they used to think. The task set for them could be worded the following way: find a way for the personal computer to identify connected analog audio devices.

In fact, a device connected across a digital interface, like USB or FireWire, can easily offer the information about itself and its characteristics to the OS. So, it is all long certain with digital peripherals, while analog devices (headphones, speakers and microphones) are usually directly attached to the audio codec and have no opportunity (or rather capacity) of sending their characteristics across the analog interface.

A majority of PC codecs are implemented on the mainboard and comply with the AC’97 specification. In other words, all AC’97 codecs have practically the same set of characteristics and work under the same specification. The interface of such a codec implies immediate operation with the input and output audio connectors. Thus, without an auxiliary detection scheme, it is a mystery to the OS what audio device is attached to the PC and if it is attached at all. Such a detection mechanism appeared in the new edition (2.3) of the AC’97 specification.

If you want to read this specification by yourself as well as to learn the differences between the 2.2 and 2.3 editions, you can follow this link.

As I have mentioned above, today it is impossible for the OS to automatically configure and control an analog device. In the nearest future we will get closer to this: the software identification of the type of the connected audio peripheral will be performed with the help of the new rules from the AC’97 specification along with the new hardware, which complies with these rules. Microsoft test lab carried out a number of experiments to find ways for the most optimal classification and grouping together of various analog audio devices (microphones, headphones, speaker systems), depending on their distinctive features. If such a distinctive quality were found, the OS could use this information to configure the audio ports depending on the type of the attached device. This way not only the audio port function will be determined (namely, whether this “input” will actually be used as an “output”, or vice versa), but also the amplification coefficient could be adjusted and the echo-muffle function might be turned on and off. When experimenting, the Microsoft engineering team focused on measuring the impedance of the electrical loop of audio peripherals. This was the distinctive feature necessary for building an ID-class table and offering requirements for the manufacturers involved. 
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