A sound card is a device (either in the form of an expansion card or a chipset) that allows the computer to handle audio information. Figure is a picture of a typical sound card. The basic responsibility of a sound card is the input, processing, and output of audio information:

• Input – Sound cards can "capture" audio information from many different sources. These sources include microphones, CD players, DAT, and MIDI devices.
• Processing – The processing capability of a sound card allows it convert audio information in different formats as well as add effects to the sound data.
• Output – Simple sound card output devices include headphones and speakers while more complicated devices consist of surround-sound digital theatre systems, DAT and CD recorders, and other musical devices.

Basic Components of a Sound Card
Even though there are many types of sound cards available for different applications, every sound card has the following basic components:

• Processor – The Digital Signal Processor (DSP) is a chip (or set of chips) that is the brain of the sound card. The DSP handles the basic instructions that drive the sound card as well as the "routing" of audio information. It can also act as the synthesizer, or music generator. 
• Converters – Digital-to-Analog (DAC) and Analog-to-Digital (ADC) converters are used in the input and output process. Most audio information recorded from outside of the computer (unless in a digital format) must pass through the ADC while data being output to speakers uses the services of the DAC. 
• Memory – More advanced sound cards use memory to store samples from musical instruments and to hold instructions for MIDI devices. This memory is usually in the form of ROM, Flash, or NVRAM and can often be upgraded or expanded. 
• Ports – Sound cards can have multiple internal and external ports for connecting to input and output devices. Also known as jacks or interfaces, these ports expand the functionality of a sound card.

Sound Production and Quality
Sound cards produce audio (synthesize) using three distinct methods. These include Frequency Modulation (FM), Wavetable, and Musical Instrument Digital Interface (MIDI). Sound cards that use FM synthesis use programming to create waveforms that best match the instrument playing. These sounds are easy to produce but are very unrealistic. Wavetable sound cards use actual digitized samples of real instruments to reproduce audio. These samples are stored within the card memory, which usually contains an entire "orchestra" of musical instruments. MIDI is a combination of hardware and software that allows the sound card to control actual musical instruments and use these instruments to output the audio. If an external instrument is not available, the sound card can use its MIDI synthesizer to play the encoded music.

The quality of a sound card is determined by its bit depth, sampling rate, and feature set:

• Bit depth – Refers to the sample size and bus size of the sound card. In general, the larger the sample size, the higher the quality of sound that is reproduced. A 32-bit sample holds a much greater amount of information about an instrument than an 8-bit sample. Also, a 32-bit sound card can "move" more data at a time than an 8-bit or 16-bit card. 
• Sampling rate – The rate at which the card can record audio information. This rate is measured in kHz, which is thousands of cycles per second. Essentially, this measures how many samples of a sound are captured within a second. CD-quality audio uses 44kHz sampling. Sound cards are now capable of sampling at 128kHz and beyond. Remember, the larger the sampling rate, the larger the digital file that will be created. 
• Feature set – Can also determine the quality of the sound card. All sound cards include the basics of a processor, converters, memory, and input/output ports, but other features can include 3-D audio co-processors, device controllers, and digital output options. 3-D audio co-processors produce "spatial" audio in multispeaker systems. This type of output is used to immerse the user in a world of sound and is popular with computer games. Sound cards can also act as device controllers that have built-in SCSI, RAID, or FireWire (IEEE 1394) controllers. Many higher-end sound cards also offer digital output ports such as Toslink (a fiber optic connector) and coaxial to allow connection to home theatre systems