The Sound card
As the name suggests, a sound card is a piece of hardware dedicated to outputting audio from a computer. Conventional stand-alone sound cards are designed to replace integrated solutions and boost audio quality for listeners. A wide range of sound cards exist to suit different uses, and are available as either internal cards designed to plug into a computer motherboard, or as external boxes that can be connected to a USB, PC Card or Firewire port.
Sound cards include dedicated chips that process the audio directly, which frees up the CPU to focus on running other applications. Internal sound cards plug into the motherboard but are a little distance from the main motherboard circuitry. As such, they tend to feature higher signal to noise ratios than their integrated counterparts. Some even include dedicated shielding, which helps reduce the interference generated by the motherboard. What all sound cards have in common is a chip designed to convert digital signals into analogue ones that can be piped to an amplifier or headphones. Current models also include digital and optical outputs that enable them to be connected directly to surround-sound amplifiers.
A little history
Prior to the early 90s, PCs had little capacity to output sound beyond basic beeps. The sound card was popularised by Creative Labs (www.creative.com.au) at the start of the 90s with its range of Sound Blaster products.
The SoundBlaster became a de facto standard for amateur audiophiles, gamers, and home users, and was quickly emulated by other hardware manufacturers. The SoundBlaster originally shipped as a monophonic card, but this quickly moved to stereo output, before Creative focused on improving sound quality. The product line has continued to evolve, but other manufacturers have caught up. Today, Creative doesn't dictate the direction of the market, though it still offers a comprehensive range of audio products, competing with brands such as Terratec, AOpen, Hercules, Philips, M-Audio and many others moving right up into professional high-end models.
The Card Itself
Sound cards are available as either internal PCI (or PC Card for notebooks) cards or external boxes. Generally an internal sound card is the way to go for a desktop PC as external solutions tend to carry a price premium. External models benefit from being easier to install and are often the only solution for notebook users or those that don't want to mess around inside their systems. Entry-level external solutions start at around $55, and range up to around $300, while internal models range between $40 and $500 and up for professional high-end models.
Modern sound solutions offer an enormous range of inputs and outputs to suit just about every connection method available, from digital input and output, Optical, and S/PDIF (Sony/Philips Digital Interface). The latter is a connection found on many higher-end audio devices that allows digital signals to be sent from device to device without having to be converted to analogue. . Digital connections are used for outputting surround-sound signals to an amplifier, while optical and analogue S/PDIF can be used to input and output audio from the sound card to a compatible amplifier or speakers.
In fact, it's the range of inputs and outputs, as well as signal to noise ratio and interface that determine the price (and target market) of a sound card. As a basic rule of thumb, the more you pay for a sound card, the higher the signal to noise ratio. Some high-end sound solutions feature an external box as well as the internal card. This allows many extra connections to be made to the card simultaneously and provides space to fit external dials for EQ and volume.