PC Hardware A Beginner’s Guide

(^550) PC Hardware: A Beginner’s Guide
 Amplitude As illustrated in Figure 21-6, the height of the sound wave is its
amplitude. This indicates the volume or loudness of the sound. If the sound
waves are tall, the volume is loud; shorter waves indicate a softer sound.
 Sample As the analog sound is being digitized, it is separated in a series of
samples (see Figure 21-7) that measure its frequency and amplitude at different
points along the sound wave. The sample records the frequency and amplitude
of the sound wave at each point. The precision of the sound’s specification is
directly affected by the number of bits used to digitally represent the samples.
 Sample size The sample size is measured in bits and governs the difference
in volume between the softest sound and the loudest sound that can be recorded
and played back. The sample size of a standard audio CD is 16 bits; for standard
broadcast radio it is 8 bits. Combined with sample rate, the sample size provides
a measure of how closely a sound file will match the original sound source.
 8-bit sound 8-bit sound is recorded using eight bits to encode its values, allowing
256 levels of specification per sample. 8-bit sound cards offer poor sound quality
that is comparable to broadcast AM radio. 8-bit audio allows 256 loudness levels.
 16-bit sound 16-bit sound uses 16-bits to specify the values of a sound sample
providing 16,000 levels per sample. This is the most common type of sound card
available; its sound is comparable to CD audio. 16-bit audio allows 65,536 loud-
ness levels.
 Sample rate The sampling rate of a sound file represents how often a sample
of a signal is taken. Sample rates are measured as samples per second. A
standard audio CD uses a sampling rate of 44.1 kilohertz (kHz), which captures
44,100 amplitude samples of sound per second. Combined with the sample size
of a sound file, the sampling rate provides a measure of how closely a sound
will match the original sound source. Other examples of sampling rates are:
 Telephone service—8 kHz
 8-bit audio file formats—22 kHz
 16-bit file formats—44.1 kHz
 DAT (digital audio tape)—48 kHz
Figure 21-6. An analog sound wave