Sound Card

Introduction to Sound Cards:-

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.

Analog vs. Digital Sounds and computer data are fundamen- -tally different. Sounds are analog - they  are made of waves that travel through matter.  People hear sounds when these waves  physically vibrate their eardrums. Computers,  however, communicate digitally, using electrical  impulses that represent 0s and 1s. Like a  graphics card, a sound card translates  between a computer's digital information  and the outside world's analog information. 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. A sound card must translate between  sound waves and bits and bytes. ADCs and DACs Imagine using your computer to record yourself talking.  First, you speak into a microphone that you have plugged  into your sound card. The ADC translates the analog waves  of your voice into digital data that the computer can  understand. To do this, it samples, or digitizes, the sound  by taking precise measurements of the wave at frequent  intervals. An analog-to-digital converter measures  sound waves at frequent intervals. The number of measurements per second,  called the sampling rate, is measured in kHz.  The faster a card's sampling rate, the more  accurate its reconstructed wave is. If you were to play your recording back through  the speakers, theDAC would perform the same  basic steps in reverse. With accurate measure- -ments and a fast sampling rate, the restored  analog signal can be nearly identical to the  original sound wave. Even high sampling rates, however, cause some  reduction in sound quality. The physical  process of moving sound through wires can also  cause distortion. Manufacturers use two measur- -ements to describe this reduction in sound  quality: • Total Harmonic Distortion (THD),  expressed as a percentage • Signal to Noise Ratio (SNR), measured  in decibels For both THD and SNR, smaller values indicate  better quality. Some cards also support digital  input, allowing people to store digital recordings  without converting them to an analog format. Methods of Sound Creation Computers and sound cards can use several methods to  create sounds. One is frequency modulation (FM) synthesis,  in which the computer overlaps multiple sound waves to  make more complex wave shapes. Another is wave table  synthesis, which uses samples of real instruments to  replicate musical sounds. Wave table synthesis often uses  several samples of the same instrument played at different  pitches to provide more realistic sounds. In general, wave  table synthesis creates more accurate reproductions of  sound than FM synthesis. Sound Card Components In addition to the basic components needed for  sound processing, many sound cards include  additional hardware or input/output conne- -ctions, including: • Digital Signal Processor (DSP): Like a  graphics processing unit (GPU), a DSP is a speci- -alized microprocessor. It takes some of the work load 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 • Sony/Philips Digital Interface (S/PDIF), a file  transfer protocol for audio data. It uses either coaxial  or optical connections for input to and output from the   sound card. • 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 Next, we'll look at integrated motherboard  and external sound control options. Options for Sound Control 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.                        External sound controller . Laptops usually have integrated sound capabilities on  their motherboards or small sound cards. However, space  and temperature control considerations make top-of- the-line internal cards impractical. So, laptop users can  purchase external sound controllers, which use USB or  FireWire connections. These external modules can  significantly improve laptop sound quality.