Before the invention of the sound card, a PC could make one sound - a beep. Although the computer could change the beep's frequency and duration, it couldn't change the volume or create other sounds. At first, the beep acted primarily as a signal or a warning. Later, developers created music for the earliest PC games using beeps of different pitches and lengths. This music was not particularly realistic -- you can hear samples from some of these soundtracks at Crossfire Designs.

Fortunately, computers' sound capabilities increased greatly in the 1980s, when several manufacturers introduced add-on cards dedicated to controlling sound. Now, a computer with a sound card can do far more than just beep. It can produce 3-D audio for games or surround sound playback for DVDs. It can also capture and record sound from external sources.

The most basic sound card is a printed circuit board that uses four components to translate analog and digital information :

• An analog-to-digital converter (ADC)



• A digital-to-analog converter (DAC)



• An ISA or PCI interface to connect the card to the motherboard



• Input and output connections for a microphone and speakers

Instead of separate ADCs and DACs, some sound cards use a coder/decoder chip, also called a CODEC, which performs both functions.

In addition to the basic components needed for sound processing, many sound cards include additional hardware or input/output connections, including :

• Digital Signal Processor (DSP) : Like a graphics processing unit (GPU), a DSP is a specialized microprocessor. It takes some of the workload off of the computer's CPU by performing calculations for analog and digital conversion. DSPs can process multiple sounds, or channels, simultaneously. Sound cards that do not have their own DSP use the CPU for processing.



• Memory : As with a graphics card, a sound card can use its own memory to provide faster data processing.



• Input and Output Connections : Most sound cards have, at the very minimum, connections for a microphone and speakers. Some include so many input and output connections that they have a breakout box, which often mounts in one of the drive bays, to house them. These connections include :

- Multiple speaker connections for 3-D and surround sound





- Musical Instrument Digital Interface (MIDI), used to connect synthesizers or other electronic instruments to their computers.





- FireWire and USB connections, which connect digital audio or video recorders to the sound card

Not every computer has a sound card. Some motherboards feature integrated audio support instead. A motherboard that has its own DSP can process multiple data streams. It may also support 3-D positional and Dolby surround sound. However, in spite of these features, most reviewers agree that separate sound cards provide better audio quality.

Inside a USB cable: There are two wires for power -- +5 volts (red) and ground (brown) -- and a twisted pair (yellow and blue) of wires to carry the data. The cable is also shielded.