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In-Depth Information
Figure 7-4
different sampling resolutions
low sample resolution
high sample resolution
Another factor affecting audio quality is the number of sound channels. Typically, the
choice is between stereo (two channels) or monaural (a single channel). Stereo provides
a richer sound than mono, but with the trade-off of approximately doubling the size of
the sound file.
The size of an audio clip is therefore related to the sampling rate, the sample resolu-
tion, and the number of channels. The total size can be expressed in terms of the bit
rate , which is the number of bits of data required for each second of sound. For music
stored on compact discs, the bit rate is determined by multiplying the sampling rate
by the sample resolution by the number of channels. A typical CD track has a bit rate
value of 1411 Kbps, which is too high for practical use on the Web. Therefore, sound
files used on the Web must employ file compression , a process that reduces the size
of the audio file but sometimes at the expense of sound quality. The most common
file compression format is the MP3 format used throughout the Web as well as on
portable music players and cell phones. MP3s can achieve near-CD-quality sound at
bit rates of 192 to 320 Kbps. The standard bit rate for MP3s is 192 Kbps, which results
in some minor sound degradation but also requires only 13% of the size required for
CD-quality sound. If a sound clip involves spoken words and not music, even greater
sound compression can be used without affecting the overall quality of the recording.
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