Hindustani music or North Indian music

Hindustani music is the traditional music of North India, i.e. just about everything from Maharashtra and northern Andhra Pradesh up. The other form of Indian classical music is Carnatic music, the music of the South. The two share some similarities; most significantly, both have a system of ragas, and quite a few ragas are shared between the two systems. However, Hindustani music is much more raga-oriented than Carnatic music. In Carnatic music, equal importance is given to mastery of raga and of tala (rhythm), whereas in Hindustani music, mastery of raga is much more important. The very structure of tala is such that the musician may leave it to the tablaist and not worry about it much (see the node on tala for details). Other similarities include an emphasis on vocal music as the most important form of music (for which reason this writeup will concentrate on vocal music); an essentially solo system, with melody very much emphasised and harmony more or less nonexistent; and an emphasis on improvisation (more so in Hindustani music).
Ragas
A raga, in Hindustani music, is very hard to define. In Carnatic music, it is almost comparable to a mode. There is no concise definition in Hindustani music. The closest is as follows: A raga is a tonal framework for composition and improvisation that creates a certain mood or emotion. Or, as Harold S. Powers put it, "A raga is not a tune, nor is it a 'modal' scale, but rather a continuum with scale and tune as its extemes." Furthermore, ragas often have associated with them particular rasas, or sentiments, as well as a certain time of day or season during which they should be sung. A few ragas are even said to be able to conjure up rain or evil spirits.
A raga consists of a set of notes relative to a tonic (base note). These notes are denoted in a manner similar to the Western sol-fa system. The names of the notes are shadj, rishabh, gandhar, madhyam, pancham, dhaivat, and nishad, usually abbreviated to sa, re, ga, ma, pa, dha, and ni. Sa and pa are always fixed, the former at the tonic and the latter at a perfect fifth from the tonic. All the rest of the notes have two versions; re, ga, dha, and ni can be lowered by a semitone; when they are, they are denoted re komal, ga komal, etc. Ma can be raised a semitone which is denoted ma tivra. A scale with all shuddh (natural) notes corresponds to a Western major scale.
A raga need not have all seven notes, but the minimum it may have is five, and must contain sa and either ma or pa. Furthermore, a raga need not have the same notes in the ascent as in the descent; it may have, for example, re shuddh on the ascent and re komal on the descent, or perhaps even not have re at all. A raga that has all seven notes in both the ascent and descent is called sampoorna (complete). A raga with six notes is called shadav, and one with five is called audav. Technically, a raga may not contain both versions of a note (such as both re komal and re shuddh), but there are quite a few exceptions. This sort of raga with more than seven notes, is called sankirna (compund) or mishra (mixed). In most ragas there will also be a vadi-samvadi (sonant-consonant) pair of notes. A note thatis frequently used with much emphasis is the vadi, and at a perfect fourth or fifth (theoretically; not always) from the vadi is the samvadi. There is not always agreement about which notes are vadi-samvadi.
But this set of notes is only the beginning, the most basic outline of the raga. The next key to the essence of a raga is the presentation, the aroh-avaroh, or ascent-descent. In Carnatic music, the aroha-avaroha is usually straightforward, from low sa to high sa, with no patterns and few embellishments. In Hindustani music, on the other hand, the aroha-avaroha is more like a tune, showing off the salient features of the raga; the aroha need not necessarily start on low sa (although it usually ends on high sa) and vice versa for the avaroha, and it can skip back and forth within the raga showing off the most prominent pakads (characteristic patterns of a raga) and gamakas (characteristic embellishments, such as grace notes, to a particular note). For example, the aroha-avaroha of a fairly common raga, Bageshri, is:
low dha, low ni komal, sa, ga komal, ma, dha, ni komal, high sa
high sa, ni komal, dha, ma, pa, dha, ma, ga komal, re, sa
The next key to understanding a raga is to hear a chalan, or melodic outline. These differ from musician to musician and depend largely on the traditional songs the musician has in mind when composing them, but there is little disagreement between musicians on the progression and pattern of well-known ragas. The final key to understanding a raga is to hear an actual performance in the raga. Without this step, one can get an idea but never an understanding of the raga (and the same goes for hearing a performance without knowing the basics of the raga). In a performance (ideally) every last detail of the raga is revealed, from how to build a little microuniverse around one note to how to build up tension moving slowly and carefully up the aroha.
Raga classification
In Carnatic music, the ragas are classified very mathematically, as shown in the Melakartha ragas. This results in some very harsh-sounding ragas that are rarely used, such as Kanakangi. Ragas in Hindustani music, on the other hand, much more of an emotional creation (similar to Carnatic ragas before the Melakartha system was codified), and so have no mathematical classification system.
From the 14th to the 19th century, the main classification system for ragas was the raga-ragini system. In this system, there were usually (many writers wrote of different raga-ragini schemes, so even in an attempt at order there was much confusion) six male, patriarchial ragas, each with five to six raginis, or wives. In addition, some had numerous sons and daughters-in-law. It is from this system we get such names as Bhairav (raga) and his wife, Bhairavi (ragini). However, around the 19th century it began to be noticed that there was much disagreement between the various raga-ragini systems, and also that there was often no similarity between a raga and his ragini (as is the case with Bhairav and Bhairavi).
Around this time, Vishnu Narayan Bhatkande compiled a monumental study of Hindustani music, and in it he developed a new system of classification by thAT, or framework. Bhatkande's system used ten sampoorna ragas: Bilaval, Khamaj, Kafi, Asavari, Bhairavi, Kalyan, Todi, Purvi, Marva, and Bhairav. In this system, all the other ragas are grouped under one of these ragas according to the notes it has. There are plenty of inconsistencies in this system, but a better one has yet to surface or be as widely accepted as Bhatkande's.
Performance
A Hindustani performance usually consists of a tanpura, and drone which provides atmosphere and keeps the singer on shruti (key); a tabla, which provides rhythm and keeps the singer on tala (beat); a harmonium, which tries to follow the singer; and, of course, the singer himself. The tanpura is a four-stringed instrument that is plucked very slowly. The first string is tuned to either Pa (most common), Ma, or Ni, whichever is most dominant in the raga. The second and third are tuned to the tonic, and the fourth is tuned to the low tonic. The tabla is tuned to the tonic. The singer usually picks one or two ragas to elaborate as the main part of his concert, as well as a few smaller ones for lighter songs at the end. The main song will either be a dhrupad or a khyal, and will consist largely of improvisation around a set framework. A instrumental main song is known as a gat. The lighter song genres include (among others) thumri, tarana, and tappar, and bandish.