Nonstreaming versus Streaming 333AudioNonstreaming versus StreamingWeb Design in a Nutshell, eMatter Editioncalledencoding. 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 thesampling 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 tele-
phone signal) and 16-bit, which is required to describe music of CD quality.
Channels
Audio files can support from one to six separate channels of audio informa-
tion. 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.
Compression
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.
Nonstreaming versus Streaming
Audio formats served via the Web fall into two general categories. Nonstreaming
audio files need to be downloaded to the user’s hard disk before they can begin
playing. Streaming audio files begin playing almost immediately and continue
playing as they are downloading. The following is a brief introduction to each
approach as well as its advantages and disadvantages. A more detailed discussion
of specific streaming and nonstreaming audio formats follows.
Nonstreaming Audio
When nonstreaming audio files (also called “static” audio) are retrieved from the
server, they must download to the hard diskin their entiretybefore they can begin
playing on the client end. Unfortunately, audio files are often quite large and