Shri Chitravina Narasimhan talks about Kala, Laya, Yati and Prastharam ,related to the Tala Dasha Pranas.
Here is a summary:
Refers to the number of Aksharas within each kriye of the tala. If there is one Akshara for each kriye it is eka kalai or 1 kalai. If there are 2 aksharas in each kriye of the tala it is dvikalai or 2 kalai. If there are 4 Aksharas in each kriye of the tala it is catuskalaior 4 kalais. One kalai is also referred to as the time duration to utter 2 Laghvaksharas, which is relative and can vary from person to person. The concept of Nadai is not separately mentioned in the Tala Dasha Pranas but the fact that 3, 5 , 7 or 9 kalais can be used within each kriye of the talam alludes to the Nadai possibilities indirectly.
Kalapramanam refers to the manner in which flow of tala is maintained constant in conjunction with the song being rendered, without fluctuating. (Equal intervals between events) There are 3 kinds of Laya based on the speed of the composition:
1) Vilamba (Cauka) – slow – includes 1st and 2nd speeds
2) Madhya Laya (Sama) – medium- includes 3rd and 4th speeds
3) Druta laya (Vega) – fast – includes 5th and 6th speeds
Yati refers to the rhythmic patterns. There are 6 varieties:
Sama Yati or Pipilika Yati (row of ants) – same pattern repeating itself
Gopucham (cows tail) – decreasing pattern – 3, 2, 1 expressed as Tkt, Tk, T
Srotovaham (river) – increasing pattern – 1, 2, 3 expressed as T, Tk, Tkt
Mridangam – Combination of Gopucham and Srotovaham to give a pattern in the shape of a mridangam or small to big followed by big to small Eg. 3 , 2, 1, 1, 2, 3 expressed as Tkt, Tk, T, T, Tk, Tkt
Damaru or Veda Madhyamam – Combination of Srotovaham and Gopucham to give a pattern in the shape of a Damaru or big to small followed by small to big Eg. 1, 2, 3, 3, 2, 1 expressed as T, Tk, Tkt, Tkt, Tk, T
Vishama – Random pattern