Sound Cards

Every year computers are becoming more important as multimedia entertainment stations.  We are seeing computers move from the office into the living room and replacing the stereo system, the video player, the karaoke machine, and even the TV.

These new ways of using the computer require specialized components such as video cards and sound cards.  Even though most motherboards have built in sound capabilities, adding an extra sound card can give you access to more audio features.

Digital Audio

Because all information in the computer is digital, sound must also be in a digital format.  At some point in the chain, however, the digital audio must be converted to analog before we can hear it.

We are accustomed to digital audio because of the popularity of CDs, but prior to the introduction of CDs in the 1980s almost all audio was analog.  An analog sound signal is a continuous representation of sound.  Digital audio attempts to reconstruct the analog signal as closely as possible, but no matter what the conversion is, there is still audio information missing in a digital signal.

The audio CD standard is 44.1 kHz at 16 bits.  This means that the analog signal is broken up into individual steps.  There are 44,100 steps per second and each step can be represented with a number up to 16 bits (65,536).  Other standards for digital audio include DVD (96 kHz at 16 bits) and DVD audio (192 kHz at 24 bits).

Before digital audio can be heard, it must be converted into an analog signal with a DAC (Digital Audio Converter). The quality of DACs varies greatly and is one of the major factors in determining the cost of a particular sound card.

Types of Audio Cards

The built-in sound processor on your motherboard uses a standard called AC 97.  This standard provides support for DVD (96 kHz, 16 bits, six channels).  The AC 97 spec does not guarantee quality -- built-in connections are usually fairly noisy and not suitable for high fidelity applications.

To get better sound and more features, you need to install a third-party audio card in one of the PCI slots of your motherboard.  The type of card that you buy will depend on what it will be used for.  If you simply wish to watch DVDs, you can get by with a basic, no-frills card.  If you wish to record music, or attach a microphone to your computer, you will probably need a more advanced card.

If you are a musician or video editor interested in sound recording applications, you may need a professional quality sound card capable of multi-track recording.

What to Look For

The published specifications on any sound card can give you a good idea of its quality.  An important number to look for is the signal to noise ratio (S/N). It compares the audio signal with the background noise. The higher the S/N ratio the better the quality. The signal to noise ratio is expressed in decibels (db) and should be at least 90db. Professional cards are often rated at more than 100db.

The number of channels the sound card supports is also important.  Surround sound cards are available in 5.1 or 6.1 configurations, and 7.1 cards are also available.  The .1 of these numbers indicates the subwoofer channel. This channel is used for low-frequency sounds and the first number tells you how many satellite speakers can be placed around the listening area.

If you're interested in using your computer to record sound, you also need to look at the number of inputs the sound card has. Standard inputs are one stereo pair, but cards designed for recording studios may have up to 10 inputs.

Prices

The prices of audio cards are a good indication of their quality.  Basic cards are available at $10 but the sound quality on them is quite poor.  Decent quality cards start at about $50 and it is possible to pay around $400 for a professional sound card.