Terminology
Each repeated cycle of a tala is called an avartan. This is counted additively in sections (vibhag or anga) which roughly correspond to bars or measures but may not have the same number of beats (matra, akshara) and may be marked by accents or rests. So the Hindustani Jhoomra tal has 14 beats, counted 3+4+3+4, which differs from Dhamar tal, also of 14 beats but counted 5+2+3+4. The spacing of the vibhag accents makes them distinct, otherwise, again, since Rupak tal consists of 7 beats, two cycles of it of would be indistinguishable from one cycle of the related Dhamar tal. However the most common Hindustani tala, Teental, is a regularly-divisible cycle of four measures of four beats each.
The first beat of any tala, called sam (pronounced as the English word 'sum' and meaning even or equal, archaically meaning nil) is always the most important and heavily emphasised. It is the point of resolution in the rhythm where the percussionist's and soloist's phrases culminate: a soloist has to sound an important note of the raga there, and a North Indian classical dance composition must end there. However, melodies do not always begin on the first beat of the tala but may be offset, for example to suit the words of a composition so that the most accented word falls upon the sam. The term talli, literally "shift", is used to describe this offset in Tamil. A composition may also start with an anacrusis on one of the last beats of the previous cycle of the tala, called ateeta eduppu in Tamil.
The tāla is indicated visually by using a series of rhythmic hand gestures called kriyas that correspond to the angas or "limbs", or vibhag of the tāla. These movements define the tala in Carnatic music, and in the Hindustani tradition too, when learning and reciting the tala, the first beat of any vibhag is known as tali ("clap") and is accompanied by a clap of the hands, while an "empty" (khali) vibhag is indicated with a sideways wave of the dominant clapping hand (usually the right) or the placing of the back of the hand upon the base hand's palm instead. But northern definitions of tala rely far more upon specific drum-strokes, known as bols, each with its own name that can be vocalized as well as written. In one common notation the sam is denoted by an 'X' and the khali, which is always the first beat of a particular vibhag, denoted by '0' (zero).
A tala does not have a fixed tempo (laya) and can be played at different speeds. In Hindustani classical music a typical recital of a raga falls into two or three parts categorized by the quickening tempo of the music; Vilambit (slow), Madhya (medium tempo) and Drut (fast). Carnatic music adds an extra slow and fast category, categorised by divisions of the pulse; Chauka (1 stroke per beat), Vilamba (2 strokes per beat), Madhyama (4 strokes per beat), Dhuridha (8 strokes per beat) and lastly Adi-dhuridha (16 strokes per beat).
Read more about this topic: Tala (music)