Dynamic intonation systems fall into two major categories: real-time and non-real-time. Non-real-time systems are typically software that converts some kind of score file with intonation information into a MIDI or audio file version of the piece. Such systems include the modified MIDI sequencers of Siegel [22][23] and Frantz [9]. In addition, most non-real-time music synthesis languages such as Csound [26] are capable of output with dynamic intonation. Real-time systems are typically software that re-maps keyboard input to MIDI output according to some set of intonation rules. Three such systems are described below. There is a rich history of experimentation in acoustic keyboard instruments with many more than 12 keys per doubling. Some of these can have dynamic intonation, but they will not be discussed here since, unlike digital electronic instruments, they are still limited to a fixed number of frequencies per doubling.