Editing Speex (section)

==== Variable Bit-Rate (VBR) ====
Variable bit-rate (VBR) allows a codec to change its bit rate dynamically to adapt to the "difficulty" of the audio being encoded. In the example of Speex, sounds like [[vowel]]s and high-energy [[Transient (acoustics)|transient]]s require a higher bit rate to achieve good quality, while [[fricative]]s (e.g. s and f sounds) can be coded adequately with fewer bits. For this reason, VBR can achieve lower bit rate for the same quality, or a better quality for a certain bit rate. Despite its advantages, VBR has two main drawbacks: first, by only specifying quality, there's no guarantee about the final average bit-rate. Second, for some real-time applications like [[voice over IP]] (VoIP), what counts is the maximum bit-rate, which must be low enough for the communication channel.