Shri Chitravina Narasimhan talks about the Suladi Sapta Talas, the origin of Chapu tala and difference between Chapu and Nadai.
Here is a summary:
The Suladi Sapta Talas were a contribution of the Dasa movement including PurandaraDasa and others. The Suladi Sapta Talas (7 talas) in order are : Dhruva Tala, Matya Tala, Rupaka Tala, Jhampa Tala, Triputa Tala, Ata Tala and Eka Tala.
There is no importance to the order in which the 7 talas are arranged. The 5 Jatis in each of these 7 talas give rise to total 35 talas which have been very useful for musical compositions. If Nadai variations (Tishra (3), Chaturashra (4), Khanda (5), Mishra (7), Sankeernam(9)) are taken into account for each of these 35 talas, total 175 talas can be derived. Along with Anga tala and Chanda talas developed by Arunagirinathar , the list of talas became exhaustive. In fact , many composers have composed pieces with the Tala as a starting point including Muthuswamy Dikshitar who composed the Vara Krithis in each of the 7 Sapta Talas.
However the number of talas used commonly today are only a small fraction of those that existed earlier. The most common tala is the Adi Tala. Other talas used are the Khanda Triputa, Mishra Jhampa, Mishra Triputa and Chapu Talas.The Chaturashra Jati Adi Tala that we use commonly today was earlier known as the Tudeeyaka Tala, and belonged to the 108 Tala system. Another Tala in the 108 system was the Turangaleela Tala which consisted of two dhrutams followed by a laghu. Although hundreds of Talas existed in the past, they became obsolete due to redundancy and gave way to better tala systems that are in vogue today. As the music became more complex and evolved, talas simplified and gave way to creative possibilities in other dimensions. The concept of Nadais is also a beautiful concept in Talas that gives rise to many creative possibilities.
Chapu Tala by default refers to the Mishra Chapu. The Chapu is also known as ‘Saippu’ Tala, meaning ‘dependent’. In the Tishra Triputa tala, there are 3 shashabdha kriyes and 4 nishabdha kriyes. The Chapu tala can be defined as one in which the tala angas are not shown explicitly and instead , only the shasabdha kriyes are highlighted. The Kalapramanam or tempo is also raised slightly. So the Mishra Chapu is derived from the Tishra Triputa where the 3 shashabdha kriyes form the main beats.
The Khanda Chapu is falsely attributed to the Tishra Rupakam in some books. This is false because this would give rise to only two beats whereas Khanda Chapu has three audible beats. A better explanation would be that the Khanda Chapu was derived from the Chaturashra Jati Matya Tala which would give rise to the requisite three audible beats.
The Sankeerna Chapu is used rarely. There is an example in the video of how the Sankeerna Chapu may be rendered slightly differently from the traditional method. Examples are given for other talas that can be rendered in Chapu format as well. The examples are given to inspire students to think differently and come up with creative ideas of their own.
The suggested method of rendering Mishra Chapu Tala with three beats is also explained in the video. The difference between chapu and nadai is that chapu is rendered with branches whereas nadai refers to the number of subunits within each beat of the tala.