Bitrates
When encoding audio, the quality of the resulting sound
depends on the sample rate and bit rate used for the
encoding. Sample rate is expressed as thousands of
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samples per second (kHz), and for CD music the sample
rate is fixed at 44.1 kHz. Bit rate is expressed as kilobits
per second (Kbps). The higher the bitrate, the better the
sound quality.
The required quality level may depend on your demands,
the headphones used, and the surrounding noise. For
MP3s a bitrate between 128 and 192 Kbps usually gives
results good enough for listening to pop music with your
device. WMA or AAC generally gives a similar result as
MP3 with one step lower bitrate (96-160 Kbps). Variations
of AAC, such as AAC+ and enhanced AAC+ (eAAC+)
provide CD quality audio at bitrates as low as 48 Kbps.
Classical music and music with nuances usually require a
higher bitrate than basic pop music.
For speech or other sources where the quality of the sound
is less important than saving storage space, you can use
bitrates between 8 and 64 Kbps. At low bitrates WMA or
AAC generally gives better results than MP3.