Industry Standard Architecture
16-bit sound card
The voice in your computer that lets you know when you've received a new
e-mail is made
possible by the sound card. Before the arrival of sound cards, personal
computers (PCs) were limited to beeps from a tiny speaker on the
motherboard. In the late 1980s, sound cards ushered in the multimedia PC and
games to a whole different level.
Creative Labs introduced the Creative Labs SoundBlaster® card. Since
then, many other companies have introduced sound cards, and Creative has
continued to improve the SoundBlaster line.
In this edition of
How Stuff Works, you'll learn how a sound card works and explore
the many uses for this technology. You will also learn what
wavetable synthesis mean.
Anatomy of a Sound Card
A typical sound card has:
- a digital signal processor (DSP) that handles most computations
- a digital to analog converter (DAC) for audio leaving the computer
- an analog-to-digital converter (ADC) for audio coming into the
- read-only memory (ROM)
or Flash memory for storing data
- musical instrument digital interface (MIDI) for connecting to external
music equipment (for many cards, the game port is also used to connect an
external MIDI adapter)
- jacks for connecting speakers and microphones, as well as line in and
- a game port for connecting a joystick or gamepad
Current sound cards usually plug into a Peripheral Component Interconnect
(PCI) slot, while some older or inexpensive cards may use the Industry
Standard Architecture (ISA) bus. Many of the computers available today
incorporate the sound card as a chipset right on the
This leaves another slot open for other peripherals. The SoundBlaster Pro is
considered the de facto standard for sound cards. Virtually every sound card
on the market today includes SoundBlaster Pro compatibility as a bare
Creative Labs SB4740 Sound Blaster 16 PCI
Often, different brands of sound cards from different manufacturers use
the same chipset. The basic chipset comes from a third-party vendor. The
sound card manufacturer then adds various other functions and bundled
software to help differentiate their product.
Sound cards may be connected to:
analog input source
- a digital input source
- digital audiotape (DAT)
- CD-ROM drive
- an analog output device - tape deck
- a digital output device
Some of the current high-end sound cards offer four-speaker output and
digital interface through a jack. For audiophiles, there is a new generation
of digital sound cards. A digital sound card is practical for
applications that need digital sound, such as CD-R and DAT. Staying digital
without any conversion to or from analog helps prevent what is called
"generational loss." Digital sound cards have provisions for digital sound
input and output, so you can transfer data from DAT,
DVD or CD directly
to your hard disk
in your PC.
Catching The Wave
Typically, a sound card can do four things with sound:
- play pre-recorded music (from CDs or
files, such as wav or
MP3), games or DVDs
- record audio in various media from external sources (microphone or
- synthesize sounds
- process existing sounds
The DAC and ADC provide the means for getting the audio in and out of the
sound card while the DSP oversees the process. The DSP also takes care of
any alterations to the sound, such as echo or reverb. Because the DSP
focuses on the audio processing, the computer's main
can take care of other tasks.
Early sound cards used FM synthesis to create sounds. FM synthesis
takes tones at varying frequencies and combines them to create an
approximation of a particular sound, such as the blare of a trumpet. While
FM synthesis has matured to the point where it can sound very realistic, it
does not compare to wavetable synthesis. Wavetable synthesis works by
recording a tiny sample of the actual instrument. This sample is then played
in a loop to re-create the original instrument with incredible accuracy.
Wavetable synthesis has become the standard for most sound cards, but some
of the inexpensive brands still use FM synthesis. A few cards provide both
Very sophisticated sound cards have more support for MIDI instruments.
Using a music program, a MIDI-equipped music instrument can be attached to
the sound card to allow you to see on the computer screen the music score of
what you're playing.
Let's say you speak into your computer's microphone. A sound card creates a
sound file in wav format from the data input through the microphone. The
process of converting that data into a file to be recorded to the hard disk
- The sound card receives a continuous, analog-waveform input signal
from the microphone jack. The analog signals received vary in both
amplitude and frequency.
- Software in the computer selects which input(s) will be used,
depending on whether the microphone sound is being mixed with a CD in the
- The mixed, analog waveform signal is processed in real-time by an
analog-to-digital converter (ADC) circuit chip, creating a
output of 1s and 0s.
- The digital output from the ADC flows into the DSP. The DSP is
programmed by a set of instructions stored on another chip on the sound
card. One of the functions of the DSP is to compress the now-digital data
in order to save space. The DSP also allows the computer's processor to
perform other tasks while this is taking place.
- The output from the DSP is fed to the computer's data bus by way of
connections on the sound card (or traces on the motherboard to and from
the sound chipset).
- The digital data is processed by the computer's processor and routed
to the hard-disk controller. It is then sent on to the hard-disk drive as
a recorded wav file.
To listen to a prerecorded wav file, the process is simply reversed:
- The digital data is read from the
and passed on to the
- The central processor passes the data to the DSP on the sound card.
- The DSP
uncompresses the digital data.
- The uncompressed, digital data-stream from the DSP is processed in
real-time by a digital-to-analog converter (DAC) circuit chip, creating an
analog signal that you hear in the headphones or through the speakers,
depending on which is connected to the sound-card's headphone jack.
Sound Card Upgrades
Sound-card upgrades are an option if the motherboard does not have a sound
chipset built in or if the user wants higher performance. A common upgrade
path is to move from an ISA sound card to a PCI sound card. Generally, your
intended application determines whether you need a new sound card. For some
audio applications, such as telephony or certain games, full-duplex sound is
a must. Full-duplex sound has the ability to accept a sound input while
simultaneously providing sound output.
In Windows, you can test for full-duplex capability by launching two
copies of Sound Recorder. To do this, click:
- Start menu
- Sound recorder
Repeat the process to launch two copies of the program. You can test for
full duplex by playing a file on one Windows Sound Recorder and, while that
file is playing, making a recording with the other.