HTML and CSS Reference
In-Depth Information
Exploring Digital Audio
If you want to add sound to your Web site, it's helpful to understand some of the issues
involved in converting sound into a format that can be played on your users' computers
and over their Internet connections. Sound is composed of combinations of sound waves;
and every sound wave can be described on the basis of two components—amplitude
and frequency. Figure 7-2 shows a basic sound wave. The
amplitude
is the height of the
sound wave and it relates to the sound's volume—the higher the amplitude, the louder
the sound. The
frequency
is the speed at which the sound wave moves and it relates to
the sound's pitch—the higher the frequency, the higher the pitch.
Figure 7-2
a simple sound wave
amp
li
tude
frequency
When you hear sound, your ears hear a continuously varying signal created by the
vibrations on your eardrum; to store that sound in a computer file, it must be converted
into discrete pieces or
bits
of information. A digital recording of that sound takes mea-
surements of the sound wave at different moments in time; each measurement is called a
sample
. The number of samples taken per second is called the
sampling rate
, a value that
is measured in kilohertz (kHz). As shown in Figure 7-3, a higher sampling rate means
that more samples are taken per second, resulting in a digital recording that more closely
matches the original sound. There is a trade-off, however, as increasing the sampling rate
also increases the size of a sound file. This might not be a problem with a CD recording,
but it can be an issue when transferring sound over an Internet connection, where it's
important to keep file sizes compact.
