Hardware Reference
In-Depth Information
This chapter focuses on the audio products found in today's PCs, their uses, and how you
select, install and operate them.
Audio Hardware Concepts and Terms
To fully understand audio hardware devices and their functions, you need to understand
various concepts and terms. Terms such as 16-bit, 24-bit CD quality, and MIDI port are
just a few. Concepts such as sampling and digital-to-audio conversion (DAC) are often
sprinkled throughout stories about sound products. You've already learned about some of
these terms and concepts; this section describes many others.
The Nature of Sound
To understand an audio adapter, you must understand the nature of sound. Every sound is
producedbyvibrationsthatcompressairorothersubstances.Thesesoundwavestravelin
alldirections,expandinginballoon-likefashionfromthesourceofthesound.Whenthese
waves reach your ear, they cause vibrations that you perceive as sound.
Two of the basic properties of any sound are its pitch and intensity.
Pitch
is the rate at which vibrations are produced. It is measured in the number of hertz
(Hz), or cycles per second. One cycle is a complete vibration back and forth. The number
of Hz is the frequency of the tone; the higher the frequency, the higher the pitch.
Humans can't hear all possible frequencies. Few people can hear sounds with frequencies
less than 16Hz or greater than about 20KHz (kilohertz; 1KHz equals 1,000Hz). In fact,
the lowest note on a piano has a frequency of 27Hz, and the highest note has a frequency
a little higher than 4KHz. Frequency-modulation (FM) radio stations can broadcast notes
with frequencies as high as 15KHz.
TheamazingcompressionratiospossiblewithMP3files,comparedtoregularCD-quality
WAV files, is due in part to the discarding of sound frequencies that are higher or lower
than normal hearing range during the ripping process.
The intensity of a sound is called its
amplitude
. This intensity determines the sound's
volumeanddependsonthestrengthofthevibrationsproducingthesound.Apianostring,
for example, vibrates gently when the key is struck softly. The string swings back and
forth in a narrow arc, and the tone it sends out is soft. If the key is struck more forcefully,
however, the string swings back and forth in a wider arc, producing a greater amplitude
and a greater volume. The loudness of sounds is measured in decibels (db). The rustle of
leaves is rated at 20db, average street noise at 70db, and nearby thunder at 120db.
