Khyal or Khayal is the modern genre of classical singing in North India. Its name comes from an Arabic word meaning "imagination". It is thought to have developed out of Dhrupad introducing frequent taans and alankaras in it. It appeared more recently than Dhrupad, is a more free and flexible form, and it provides greater scope for improvisation. Like all Indian classical music, khyal is modal, with a single melodic line and no harmonic parts. The modes are called raga, and each raga is a complicated framework of melodic rules.
Khyal bases itself on a repertoire of short songs (two to eight lines); a khyal song is called a bandish. Every singer generally renders the same bandish differently, with only the text and the raga remaining the same. Khyal bandishes are typically composed in a variant of Urdu/Hindi or occasionally Farsi, Bhojpuri, Punjabi, Rajasthani, Marathi or Sanskrit. These compositions cover diverse topics, such as romantic or divine love, praise of kings or gods, the seasons, dawn and dusk, and the pranks of Krishna, and they can have symbolism and imagery. The bandish is divided into two parts -- the sthayi (or asthayi) and the antara, with the former considered more important as it shows the melodic contours of the raga. The sthayi often uses notes from the lower octave and the lower half of the middle octave, while the antara ascends to the tonic of the upper octave and beyond before descending and linking back to the sthayi. The singer uses the composition as raw material for improvisation, accompanied by a harmonium or bowed string instrument such as the sarangi or violin playing off the singer's melody line, a set of two hand drums (the tabla), and a drone in the background. The role of the accompanist playing the melody-producing instrument is to provide continuity when the singer pauses for breath, using small variations of the singer's phrases or parts thereof. While there is a wide variety of rhythmic patterns that could be used by the percussionist, khyal performances typically use Ektaal, Jhoomra, Jhaptaal, Tilwada, Tintal, Rupak, and Adachautaal.
A typical khyal performance uses two songs -- the bada khyal or great khyal, in slow tempo (vilambit laya), comprises most of the performance, while the chhota khyal (small khyal), in fast tempo (drut laya), is used as a finale and is usually in the same raga but a different taal. The speed gradually increases over the time of the performance. The songs are sometimes preceded by improvised alap to sketch the basic raga structure without drum accompaniment; unmetered alap is given much less room in khyal than in dhrupad.
As the songs are short, and performances long (half an hour or more), the lyrics lose some of their importance and abstract musical values are emphasized. Improvisation is added to the songs in a number of ways: for example improvising new melodies to the words, using the syllables of the songs to improvise material (bol-baant, bol-taans), singing the names of the scale degrees -- sa, re, ga, ma, pa, dha and ni (sargam) -- or simply interspersing phrases sung on vowels, usually the vowel A, akaar taans. Taans are one of the major distinguishing features of the khyal. Now and then, the singer returns to the song, especially its first line, as a point of reference. Besides the vilambit (slow) and drut (fast) tempos, a performance may include ati-vilambit (ultra-slow), madhya (medium speed) and ati-drut (super-fast) tempos. Song forms such as taranas, thumris or tappas are sometimes used to round off a khyal performance.
Khayal was popularized by Niyamat Khan (a.k.a. Sadarang) and his nephew Firoz Khan (a.k.a. Adarang), both musicians in the court of Muhammad Shah Rangile (1719-1748). It seems likely that khyal already existed at the time, although perhaps not in the present form. In around 1705, Guru Gobind Singh, the tenth master of Sikhism, wrote a Khyal after the Battle of Chamkaur:
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mithr piaarae noo(n) haal mureedhaa dhaa kehinaa ?
thudhh bin rog rajaaeeaa dhaa oudtan naag nivaasaa dhae hehinaa ?
sool suraahee kha(n)jar piaalaa bi(n)g kasaaeeaaa(n) dhaa sehinaa ?
yaararrae dhaa saanoo(n) saathhar cha(n)gaa bhat(h) khaerriaa dhaa rehinaa ?
English translation, from Sikh Wiki:
Tell the beloved friend (the Lord) the plight of his disciples.
Without You, rich blankets are a disease and the comfort of the house is like living with snakes.
Our water pitchers are stakes, our cups have edges like daggers.
Like the suffering of animals at the hands of butchers.
Our Beloved Lord's straw bed is more pleasing to us than living in costly furnace-like mansions.
The compositions of Sadarang and Adarang employ the theme of Urdu love-poetry. The khyal of this period also acquired the dignity of Dhrupad and the manner of the veena in its glide or meend, plus a number of musical alankars that were introduced into the body of the composition. The gharana system arose out of stylistic rendering of the khyal by various subsequent generations of musicians. The gharanas have distinct styles of presenting the khyal -- how much to emphasize and how to enunciate the words of the composition, when to sing the sthayi and antara, whether to sing an unmetered alap in the beginning, whether to do bol-alap or aakar-alap, what kinds of improvisations to use, how much importance to give to the rhythmic aspect, and so on.
With India united into a country from various scattered princely states, with royal courts and the zamindari system abolished, and with modern communications and recording technology, stylistic borders have become blurred and many singers today have studied with teachers from more than one gharana. This used to be uncommon, and a few decades ago teachers used to forbid students to even hear other gharana singers perform, not allowing them to buy records or listen to the radio. Today, as always, a singer is expected to develop an individual style, albeit one that is demonstrably linked to tradition.