North is different to South Indian music. South Indian music is more tightly structured and generally used as accompaniment to dance, where you really see it come into it's own.
North Indian music has a big Islamic influence. When you think of the Islamic influence, keep in mind that the Islamic expression found in earlier times, like the vast Persian Empires, when Islam as a religion ruled from China to Spain, was not the conservative repressive style of Islam we tend to think of today.
Islam back then was a broad rich culture, with fostered interests in science, art and knowledge in all things.
The Islam influence brought to Indian music a freedom and poetic beauty. Thus it opened out, and provided free-form expression for the musicians. This is what you find in North Indian music - much like free-form jazz today.
The basics:
Raags are primarily scales - certain notes to be use in ascending or descending. But more than that, they are also images. Performed at particular times of the day, the musician gradually builds an image of the raag in aural form.
The typical raag will have a beginning section where the melodic instrument has freedom from rhythmic structure - this is a very poetic section where the musician can explore all the nuances of the raag and his instrument. Next there will be a number of sections played with the drummer, usually in increasing speeds.
Almost always they begin slowly and gently, building into highly dramatic speeds and interactions.
The other instrument is the tanpura - this instrument plays a single chord, tuned to that of the raag. Finger picking style, it is not easy to play correctly - must be smooth, graceful and consistent.
At times other instruments can be brought in, but these three are the core of Indian music: drone, drum, melodic instrument (sitar, voice, flute etc).
This is a perfect combination. It allows maximum musical improvised expression. As soon as more instruments are brought in, and you have harmonies or pre-arranged melodies, the freedom of the musician to spontaneously create is restrained.
Improvisation is the corner-stone of Indian music, especially North Indian - improvisation was encourage by the Islamic influence. It is a beautiful combination, where freedom and cooperation are optimised - cooperation in rhythm and freedom in melody or rhythmic syncopation. That structure offers perhaps the best advantages for the musician to fully explore their art and creativity.
The rhythm is a fairly slow beet comprising a set number of beets within a cycle. The most common is 16 beets (tintal), divided into sections of 4 x 4. The emphasis is on the first beet, so '1' is not only emphasised each time around, but is also usually struck together by the drum and the melodic instrument - they also finish on the first beet of the cycle, as opposed to Western and African music which usually finishes on the last or second-last beet of a cycle.
Thus the critical beets for tintal are 1, 5, 9, 1. The 9th beet is a special one, and often treated differently. The last section has hundreds of variations which the musicians know, so they are able to land on the 1 from all kinds of weird variations. I am told there are hundreds, but usually you will hear the use of only about a dozen or two variations.
Always remember that the musicians are building a mood. That is the key to appreciating Classical Indian music. It is a spiritual journey, and should not be listened to with the same ears you listen to other kinds of music with. It is designed to be played to a very knowledgeable and attentive audience.
Here is one of the best examples of North Indian Classical music I have. It is singing by a woman who's name I know not. It is an excellent example of dream-like floating which is not designed to go anywhere. It is very long, and thus this file is just over 100 MB. This piece doesn't speed up much - it effortlessly drifts on the ether forever.
North Indian Classical Singing