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Chapter 19. Audio on the Web > Basic Digital Audio Concepts

19.3. Basic Digital Audio Concepts

In order to distribute recorded speech or music over the Internet, the analog audio must be converted to a digital format (described by bits and bytes). This process is called encoding . It is analogous to scanning a photograph to a digital bitmap format, and many of the same concepts regarding quality and file size apply.

Sampling Rate

To convert an analog sound wave into a digital description of that wave, samples of the wave are taken at timed intervals. The number of samples taken per second is called the sampling rate. The more samples taken per second, the more accurately the digital description can recreate the original shape of the sound wave, and therefore, the better the quality of the digital audio.

Sample rates are typically measured in kilohertz (KHz). On the high end, CD-quality audio has a sampling rate of 44.1 KHz. On the low end, 8 KHz produces a thin sound quality that is equivalent to AM radio. Some standard sampling rates include: 8 KHz, 11.025 KHz, 11.127 KHz, 22.05 KHz, 44.1 KHz, and 48 KHz. The higher the sampling rate, the more information is contained in the file, and therefore the larger the file size.

Bit Depth

Like images, audio files are also measured in terms of their bit depth (also called sampling resolution or word length). The more bits, the better the quality of the audio, and of course, the larger the resulting audio file.

Some common bit depths are 8-bit (which sounds thin or tinny, like a telephone signal) and 16-bit, which is required to describe music of CD quality.


Audio files can support from one to six separate channels of audio information. The most familiar of these are mono (1 channel) and stereo (2 channels), but some formats can support 3-channel, quadraphonic, and 4- or 6-channel surround sound.


Some audio file formats (such as MPEG and AIFF/C) are compressed using a specialized audio compression algorithm in order to save disk space. MPEG uses a lossy compression scheme (it strips out sounds that are not discernible to the human ear) to achieve very high compression ratios (from 4:1 to 12:1) while maintaining near-original sound quality.



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