This was the subject on which Sumitra Vasudev presented this morning.
The Sangita Ratnakara (SR) she said, speaks of the gamaka as a movement involving several notes as opposed to just one as is understood nowadays. The Sangita Samaya Sara (SSS) of Parhsvadeva of the 13th century speaks of gamaka from the context of conveying or revealing the svarupa. It shows the subtle tones that come in when singing on a particular note. These concepts are accepted even today and it is remarkable that what was thought of in the 13th century applies even now.
There is a reference to gamakas in the Brhaddesi of Mathanga (7th century AD) and this can be taken to be the earliest reference. The Sangita Makaranda of Narada (11th century) speaks of 19 types of gamakas. The work also splits ragas into 3 categories – muktanga kampita (permitting extensive oscillation), arhda kampita (moderate) and kampita vihina (not permitted)
The SR says that there are 15 types of gamakas and this is a classification that is broadly accepted even now. However Sarngadeva defines the gamaka to be just a part of the practical aspects of music. Thus gamakas are dealt with by him in the SR neither in the ragadhyaya or the svaradhyaya but in the prakirnakadhyaya.
In the 17th century, Venkatamakhin in his Chaturdandi Prakasika deals with gamakas. He accepts the definitions of the SR and the SSS and states that there are 15 types though his classification makes a few changes. He says that gamakas are an aspect of the svara. His contemporary, Somanatha in his Raga Vibodha includes gamakas under techniques of playing and deals with the dholanam (earlier sphuritam) only. He classifies gamaka as a vadanabhida (variety in playing) and also states that the gamaka is a nadamaya or that which manifests.
There are a few subsequent works which are not well known which also deal with gamakas. But it is the early 20th century Sangita Sampradaya Pradarsini which is the most exhaustive. Here the gamaka becomes a thread that binds all factors together – raga, svara, phrases and the manifestation of a raga is only through the gamaka. The author Subbarama Dikshitar states that nobody would sing without gamaka. He also states that several ragas may have the same arrangement of notes and it is only through the gamaka that their individuality is established. Each raga is described in this work in terms of the gamakas in it. Several types of gamakas as illustrated in the SSP were demonstrated by the speaker.
She concluded by stating that while it is mandatory now to define a raga by its gamakas, it is also interesting that a final picture of a raga can emerge only by the elimination of what is unsuitable. (A neti neti doctrine?)