The Taiwan-based motherboard maker AOpen, part of the Acer Group, came up with a very interesting gimmick in June 2002 when it introduced the world's first PC motherboard with a vacuum tube–based audio amplifier—the AOpen AX4B-533 Tube. The motherboard was based on the Intel 845E chipset, and uses a Realtek ALC650 AC'97 audio codec chip. At first, many PC users wondered whether this was an April Fool's joke that showed up late. Why a vacuum tube? AOpen engineers pointed out that serious audiophiles have continued to use vacuum-tube amplifiers because of their rich sound. They felt that audiophiles would pay a premium price for similar technology in the sound circuitry of a PC. AOpen used the following design features to bring the vacuum tube into the twenty-first century:
A switching mode power supply to provide adequate tube power. Tubes fell out of favor in the late 1950s because they require more power than transistors and integrated circuits.
A dual-triode. This design has one tube with two front stereo channels and is modeled after the design used by classic pre-amp circuits, which can also accept input from standard sound cards.
Frequency isolation wall (FIW) noise reduction. This shields the tube circuitry from the normal EFI/RFI interference inside the computer.
High mean time between failure (MTBF) design for motherboard and tube circuitry.
The additional circuitry used by the AX4B-533 Tube made it one of the most expensive motherboards using the 845E chipset (see Figure 16.9). However, it has received rave reviews from many computer publications and users for audio quality, performance, and (not least) the snob appeal of having the first motherboard on the block like it.
Figure 16.9A close look at the A4XB-533's vacuum tube sound system.
The AX4B-533 Tube's audio quality is optimized for classical and jazz music listening. AOpen has now released additional vacuum-tube-based motherboards: the AX4GE Tube and AX4PE Tube for Pentium 4 processors and the AK79G Tube for Athlon XP processors. These motherboards are optimized for rock and pop music thanks to a slightly revised tube and amplifier design.
One of the biggest issues for serious game players when audio adapters are considered is how well they perform 3D audio tasks. This has been complicated by several factors, including the following:
Differing standards for positional audio
Hardware versus software processing of 3D audio
DirectX support issues
The underlying issue common to all 3D sound cards is that of positional audio, which refers to adjusting features such as reverberation; balance; and apparent sound "location" to produce the illusion of sound coming from in front of, beside, or even behind the user. One very important element in positional audio is HRTF (Head Related Transfer Function), which refers to how the shape of the ear and the angle of the listener's head changes the perception of sound. Because HRTF factors mean that a "realistic" sound at one listener's head angle might sound artificial when the listener turns to one side or the other, the addition of multiple speakers that "surround" the user, as well as sophisticated sound algorithms that add controlled reverberation to the mix, are making computer-based sound more and more realistic.
Creative Labs' Environmental Audio Extensions (EAX) has become the de facto standard for 3D audio since the demise of Aureal's A3D in mid-2000. There are four versions of EAX:
EAX Advanced HD (also known as EAX 3.0)
EAX 4.0 Advanced HD
EAX 1.0 introduced 26 presets designed to simulate the audio effects caused by typical building and natural environments along with the capability to adjust volume, reverberation, decay time, and damping. EAX 2.0 adds occlusions (how sound originating in one room is heard in another room) and obstructions (how sound is heard when an object blocks direct sound waves and only reflections can be heard).
EAX 1.0 and EAX 2.0 are supported both by Creative's Sound Blaster and Audigy series of sound cards but also by most recent third-party sound cards and integrated audio solutions, thanks to Creative's release of these standards to the industry.
EAX Advanced HD, introduced by the Sound Blaster Audigy, adds support for multienvironment—each sound (up to four) can have its own environmental effects. It also adds environment morphing, environment panning, and environment reflection, three methods used to change environment sounds as the player moves through the game. Environmental filtering fine-tunes how sounds change from environment to environment. Audigy 2's version of EAX Advanced HD adds the capability to convert DirectX 3D audio (Direct3D) into 6.1 audio on systems with 6.1 speaker systems. EAX Advanced HD supports up to 32 channels of Direct 3D hardware voice acceleration.
EAX 4.0 Advanced HD, introduced by the Sound Blaster Audigy 2 ZS, adds sound effects such as pitch and frequency shifting, automatic gain control compression, a wah-wah pedal, chorus, distortion, a whooshing effect (flanger), and a ring modulator. EAX 4.0 Advanced HD also adds a comb filter to remove audio artifacts, HRTF filters, cross-talk cancellation algorithms that support speaker types from headphones (2.0) up through 7.1, and 64 channels of Direct 3D hardware voice acceleration.
Note - Audigy 2 cards (but not the low-end Audigy LS) can also use EAX 4.0 Advanced HD through a driver update.
The major alternative to EAX is Sensaura's 3D positional audio technology (3DPA). Most third-party sound cards support Sensaura 3DPA along with EAX 1.0/2.0. The full range of Sensaura 3DPA features include
Digital Ear. HRTF filters
Virtual Ear. Customizes Digital Ear for the listener's ear size and positioning
MacroFX. Improves realism of close sound sources, such as a buzzing insect
ZoomFX. Improves realism of sounds from different sizes of objects, such as trains versus motorcycles
EnvironmentFX. Preset environments with adjustable properties
XTC and MultiDrive. Crosstalk cancellation for speaker systems up to 7.1
Headphone Theater. Simulates 5.1 audio for headset users
Note - Some audio cards that use Sensaura 3DPDA technology might not support all the features, or they might require a software upgrade. Contact your audio card or motherboard vendor for details.
This chapter is from Upgrading and Repairing PCs, 16th edition,by Scott Mueller. (Que Books, 2004, ISBN: 0789731738). Check it out at your favorite bookstore today.
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