In Indian classical music, specific musical modes for improvisation are called ragas. The melodic elements of a raga are played on musical instruments. Ragas are differentiated by the notes in the mode as well as specific tones in the ascending scale called the arohana, which often differ from the descending scale, known as avarohana. The overarching structure of a raga is known as a chalan, which is the core melody and framework for improvisation of the raga. Every raga has a chalan, which presents the essential makeup of the structure of the raga.