How Sound Cards Work

useumpireSoftware and s/w Development

Dec 2, 2013 (3 years and 6 months ago)

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How Sound Cards Work

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
.


Fortun
ately, 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.


In this article, you'll learn how a
sound card allows a computer to create and record real, high
-
quality
sound.

Analog vs. Digital

Sounds and computer data are fundamentally 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.


Sound is made of waves that travel through a medium, such as air or water.

The most basic sound card is a printed circ
uit 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 a
nd DACs, some sound cards use a coder/decoder chip, also called a
CODEC
,
which performs both functions.

In the next section, we'll explore the analog
-
to
-
digital and digital
-
to
-
analog conversions that take place
on the sound card.


An analog
-
to
-
digital con
verter measures sound waves at frequent intervals.


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.

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
, the DAC would perform the same basic
steps in reverse. With accurate measurements and a fast sampling rate, the restore
d 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 measurements t
o
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.

Next, we'll look at the other components commonly found on sound cards and what they do.

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 tabl
e 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.


A PCI sound card


Other Sound Car
d Components

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, simul
taneously. 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

G
ame designers use
3
-
D sound

to provide fast
-
paced, dynamic sound that changes based on a player's
position in the game. In addition to using sound from different
directions, this technology allows realistic
recreations of sound traveling around or through obstacles.
Surround sound

also uses sound from
several directions, but the sound does not
change based on the listener's actions. Surround sound is
common in
home theater

systems.

Like a
graphics card
, a soun
d card uses software to help it communicate with applications and with the
rest of the computer. This software includes the card's drivers, which allow the card to communicate
with the
operating system
. It also includes
application program interfaces

(APIs), which are sets of rules
or standards that make it easier for software to communicate with the card. The most common APIs
include:



Microsoft: DirectSound



Creative: Environmental Audio

Extensions (EAX) and Open AL



Sensaura: MacroFX



QSound Labs: QSo



Next, we'll look at integrated
motherboard

and external sound control options.

3
-
D vs Surround Sound and Drivers & APIs

G
ame

designers use
3
-
D sound

to provide fast
-
paced, dynamic sound that changes based on a player's
position in the game. In addition to using sound from different directions, this technology allows realistic
recreations of sound traveling around or through obs
tacles.
Surround sound

also uses sound from
several directions, but the sound does not change based on the listener's actions. Surround sound is
common in
home theater

systems.

Like a
graphics card
, a sound card uses software to help it communicate with applications and with the
rest of the computer. This software includes the card's drivers, which allow the card to communicate
with the
operating system
. It also includes
application program interfaces

(APIs), which are sets of rules
or standards that make it easier for software to communicate with the card. The most common APIs
include:



Microsoft: DirectSound



Creative:
Environmental Audio Extensions (EAX) and Open AL



Sensaura: MacroFX



QSound Labs: Qsound


Other Options for Sound Control


External sound controller

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.

Laptops usually have integrated sound capabilities on their motherboards or small sound cards.
However, space and temperature control consid
erations 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.

Shopping for a Sound Card

Numerous factors affect a sound card's abilities to provide clear, high
-
qualit
y sound. When
shopping for a sound card, pay attention to:



ADC and DAC data capacity, measured in
bits



Signal
-
to
-
noise ratio (SNR) and total harmonic distortion (THD)



Frequency response, or how
loudly the card can play sounds at different frequencies



Sampling rate



Output channels, such as 5.1 or 7.1 surround sound



Supported application programming interfaces (APIs)



Certifications, including Dolby Master and THX

Anyone investing in a top
-
of
-
the
-
li
ne sound card should also have high
-
quality
speakers
. Even
the best sound card cannot compensate for poor speaker quality.



Article courtesy of howstuffworks .com