The system may be designed to tolerate a large variety of speaker variabilities. In this case the system is speaker independent and has to deal with a large population of users, mainly from the general public .
Other systems may be tuned to the voice of a particular speaker (a single speaker) and thus the system is speaker-dependent. We may also have a system that is adapted to the voice of a particular set of speakers (multi-speaker system ).
Some systems may also be adapted to be utilised only by trained speakers instead of the general public (untrained speakers). Others may be used by consistent or inconsistent speakers, skilled users/unskilled users, a specific ``population'', or the general public . Some may be used, for a given language, by native speakers or by speakers with foreign or heavy (regional) accents .
In order to achieve speaker independency a training phase is usually needed and uses a specified type of speech corpus. The characteristics of the required speech data have to be described in terms of