The basis of raagas are swaras. A Carnatic singer can choose a base pitch that he or she is comfortable with and that becomes his/her sruthi. An octave is the range of frequencies that start with this base pitch and end at twice the frequency, at which point the next octave starts. Good artists try to demonstrate their range by singing in three octaves. Each octave is further divided into twelve perceptible frequencies or swaras (notes). They are S, R1, R2(=G1), R3(=G2), G3, M1, M2, P, D1, D2(=N1), D3(=N2), and N3. S and P are immutable frequencies and other notes have different frequencies.
The second aspect of the raaga is the gamaka through which emotion is invoked. In simple terms a gamakam is an oscillation from one note/pitch to another and a return to the original note. This means that mutable notes could be sung with slightly varying frequencies, but there are rules to be followed. Not every swara is "shaken" in a raaga. Each raaga has its own set of "jiva" swaras and the embellishments are focused around these to bring the life of the raaga.
All these make identifying a raaga a complex task that comes with training the brain towards pattern recognition. Humans have an advantage over machines when it comes to raaga recognition. A concert recording can have many instruments, ambient noise etc., from which a signal processor should be able to isolate the frequency that is playing the melody, which follows a raga. After this is achieved, the base sruthi of the singer has to be determined from the set of frequencies sung by the singer, to identify swaras. Finally, raagas can be identified by patterns and phrases of notes, rather than by notes with absolute frequencies. This may require a huge volume of training data and pattern matching algorithms. Raaga identification programs using machines are still in their infancy.
The best way to learn to identify raga is to listen to a lot of music. Effort should be made to find out the raaga of the song. The song and mood should be associated with the raaga. After a few days, some songs would appear to be similar. Repeated listening to same raaga by various artists would eventually etch the pattern to memory. For beginners, the following pentatonic ragas (ragas with five notes) are suggested to start with
Once the concept of a raaga pattern is learnt, it becomes easy to abstract the concept and learn many raagas. Music students have more exposure to the technicalities of a raaga. Apart from knowing the arohanam and avarohanam, students learn the prayogams and sancharas. Practicing akaaram helps with memorizing the pattern of a raaga. Learning music theory makes the process of identifying raagas more methodical. Knowledge about how raagas are constructed, the swaras behind them, arohanam and avarohanam helps the listener to derive a raaga. The base swara could be derived from the drone or the sruthi box and with the knowledge of identifying swaras, it becomes easy to derive the raga.
There are several resources available on the Internet that can explain aspects of ragas and play list of songs, including references to popular light music. Sangeethapriya.org is a popular website for Carnatic fans to listen to content uploaded by other fans. Carnatic radio app brings Carnatic music 24x7 to mobile phones. The best part is that these resources are free.
At Hamsadhwani, students and rasikas alike can benefit from the wealth of live and recorded concerts, interacting with the artists, various workshops and presentations. Recorded songs are carefully coded with the name of the raaga in the title, to make it easy for the patrons to listen and appreciate raagas in Carnatic music. Effort is taken to display raagas during live concerts. Attending live concerts and having discussions about the concerts helps in raaga appreciation.
All these strategies combined will help one in slowly becoming proficient at identifying raagas. Learning is not easy and it is time consuming, but it could be very rewarding and helps one fully appreciate the beauty of Carnatic music. With the awareness of raaga, one gets engaged deeply with the performance, resulting in an exhilarating experience. That Eureka moment when the raaga name flashes is priceless!