Integrated Audio Chips

The Intel 810 chipset was the first mainstream chipset for a major CPU to integrate audio; it works with Celeron CPUs. Its inspiration might have been the Cyrix/National Semiconductor Media GX series, which used a trio of chips to substitute for the CPU, VGA video, onboard audio, memory, and I/O tasks.

Thanks to improvements in chipset design and faster CPU performance, today's best integrated chipsets can provide solid mid-range performance. Almost all recent chipsets from Intel, VIA, ALi, and SiS have integrated audio. In almost every case, integrated audio supports the AC'97 audio standard.

AC'97 Integrated Audio

The phrase AC'97 integrated audio can be found in the descriptions of most recent systems. Because AC'97 can replace the need for a separate audio card but might not be a satisfactory replacement, you need to understand what it is and how it works.

AC'97 (often referred to as AC97) is an Intel specification that connects an audio codec (compression/decompression) architecture to a section of a South Bridge or an I/O Communications Hub chip called the AC-Link control. The AC-Link control works with the CPU and an AC '97 digital signal processor (DSP) to create audio.

The AC'97 audio codec could be a physical chip on the motherboard, a chip on a small daughterboard called a communications and networking riser (CNR), or a software program. Thus, a motherboard with AC '97 integrated sound support doesn't require the use of a separate audio card for sound playback.

Sometimes AC'97 is also used to refer to audio chips on a sound card, but in this discussion we will use it to refer only to integrated audio. Sometimes motherboards also integrate an analog modem through an MC '97 codec chip, or they might have an AMC '97 (audio/modem) codec chip to combine both functions.

It's important to realize that, although most recent chipsets support AC'97 audio, this does not mean that every motherboard built on a particular chipset uses the same AC'97 codec, or even the same method of creating sound. In most cases, AC'97 is implemented through a small AC'97 codec chip on the motherboard. It can be surface-mounted, but many vendors use a small socket instead.

For various reasons, including features and price, different motherboard vendors might use different AC'97 codec chips on motherboards that use the same chipset.

The drivers for a particular AC'97 codec chip are supplied by your motherboard vendor because they must be customized to the combination of codec and South Bridge/ICH chip your motherboard uses.

Although the AC'97 specification recommends a standard pinout, differences do exist between AC'97 codec chips. Some vendors of AC'97 chips provide technical information to help motherboard builders design sockets that can be used with different models of the AC'97 codec chip.

The four versions of the AC'97 codec are as follows:

  • AC'97 1.0. Has fixed 48KHz sampling rate and stereo output

  • AC'97 2.1. Has options for variable sampling rate and multichannel output

  • AC'97 2.2. Has AC'97 2.1 features plus optional S/PDIF digital audio and enhanced riser card support; released in September 2000

  • AC'97 2.3. Has AC'97 2.1/2.2 features plus support for true Plug and Play detection of audio devices; released in July 2002

Most motherboards with integrated audio support AC'97 2.1 or 2.2 at this time. To learn more about the AC'97 specifications, see the Intel – Research and Development, Audio Codec. To determine whether a particular motherboard's implementation of AC'97 audio will be satisfactory, follow these steps:

  1. Determine which codec chip the motherboard uses. Read the motherboard manual or see which driver the motherboard uses for audio.

  1. Look up the chip's features and specifications. If you are not sure of the chip manufacturer, look up the part number with a search engine such as Google.

  1. Use a search engine to find reviews of the chip's sound quality and performance (typically found as part of a motherboard review). The Web site 3D Sound Surge reviews both sound cards and motherboards/audio codecs.

  1. Look at the motherboard's features to determine whether it uses the full capabilities of the codec chip. Chips that support AC'97 2.1 can offer up to six-channel analog audio; those that support AC'97 2.2 can also offer S/PDIF digital audio. However, motherboard makers don't always provide the proper outputs.

  1. Analyze how you use audio. If you play a lot of 3D games, you're not likely to be satisfied with the performance of any integrated audio solution, no matter what its features might be. You can disable onboard audio with a BIOS setting if you prefer to install your own audio card.

AOpen TubeSound

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 AC97 sound 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 AX4B-533 Tube is among the most expensive motherboards using the 845E chipset. 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.

The AX4B-533 Tube's audio quality is optimized for classical and jazz music listening. AOpen has now released two additional vacuum-tube-based motherboards: the AX4GE Tube and AX4PE Tube, which are optimized for rock and pop music thanks to a slightly revised tube and amplifier design.