The drone is an essential part of traditional Indian music. It is found in classical music (both North and South), folk music, and even many film songs. Sometimes, it is provided by special instruments and instrumentalists; at other times, it is provided by special parts of the melodic instruments. Even many of the percussion instruments are tuned in such a way as to reinforce the drone. Regardless of what provides the drone, it serves a vital function.
The function of the drone is to provide a firm harmonic base for the music. Although this may not be intuitive, it is not difficult to understand. A contrast between Indian and Western music is a good way to illustrate the drone's function.
The tonic in Western music is implicit in the scale structure. There are amazingly few modes used in Western music, so the mind unconsciously looks at the intervals between the notes (e.g., whole-step, whole-step, half-step, etc.), and uses this structure to identify the tonic. The numerous modes used in Indian music make this process nearly impossible. Since virtually any combination of intervals may be found, it is clear that another process for identifying the tonic must be used.
It is the drone which functions to unambiguously establish the tonic. The continuous sounding of one or more notes provides the harmonic base for the performance. This not only clarifies the scale structure, but actually makes it possible to develop amazingly complex modes. These modal explorations are possible because of subtle, yet profound harmonic phenomena. These harmonic phenomena are very adequately explained in Helmoltzian terms. Different levels of consonance and dissonance result from the physical interaction of the tones of the melody with the tones of the drone (Jairazbhoy 1971).
Indian drones may utilise anything from a single note to all of the notes of the scale. The complexity of the drone has an important bearing upon the feel of the performance.
The simplest drone consists of a single note repeated indefinitely. When only a single note is used, it must be the Sa (shadaj) of the piece. Single note drones may be found in folk music (e.g., ektars) but sometimes they may be found in classical music. A single note is all that is required to define the modality of the piece.
More complicated harmonic effects may be produced by having two notes in the drone. Both Hindustani sangeet as well as Carnatic sangeet tend to use the first and the fifth (e.g., Sa-Pa) as a drone. Folk music on the other hand, permits many other combinations. The dotar for example may be tuned to a variety of intervals.
Occasionally, drones are even more complex. For example, five, six, and even seven-string tanpuras are available that provide far more than a simple Sa-Pa drone. The surmandal contains all of the notes of the scale spread over several octaves. Although these lush drones are available, there is a tendency to use them judiciously; otherwise the performance may become muddy and the modes indistinct.
Indian music displays a curious overlap between the drone accompaniment and rhythmic accompaniment. It is very normal for instruments, or parts of instruments to be considered to provide either a rhythmic support or a drone. Ektars and dotars may be considered either drone instruments or rhythmic instruments because they perform both functions. The same can be said for the chikari strings of the sitar or the thalam strings of the vina. Even the mridangam and the tabla, which are considered by many to be the ultimate rhythmic instruments, continuously drone the tonic through the performance. We find that instruments whose only function is to drone (e.g., tanpura, surpeti) are few compared to the large number of instruments with dual functions.
It is appropriate for us to confine our discussion to the use of drones with the various north Indian rags. Heretofore, we have discussed the drone in very broad terms, but it is now appropriate for us to narrow our focus.
In Hindustani sangeet, there is a tendency to think of the drone as a two-note musical device. As a practical matter, it is easy to think of this as being composed of a primary drone and a secondary drone. The primary drone will be (Sa) and there will be one other note as the secondary drone.
It is obligatory that the primary drone be Sa. One may find several different drones of Sa spread across several octaves. For instance, a stringed instrument such as the sitar, may have several strings set to the Sa in different octaves, but at least one Sa must always be present. Just as Sa can never be completely omitted from any rag, in a similar manner, Sa cannot be eliminated from the drone.
The secondary drone is up to the discretion of the artist. If this note is chosen unwisely, it can destroy the entire mood of a rag. Fortunately, an easy rule of thumb is to use the fifth (pancham). This works so often that one seldom has to give it a second thought. Unfortunately, there a a few rags whose performance may be ruined by the presence of the 5th.
Here is an easy way to determine what the secondary drone should be.
This last situation deserves some explanation. One should never use tivra Ma as a secondary drone; the reason for this is simple. Since the interval between Sa and tivra Ma is the same interval as tivra Ma to the higher Sa, it leaves the entire performance ungrounded. The listener tends to get confused as to which is the Sa and which is the tivra Ma. It therefore, leaves the modality of the entire piece in question. A good visual analogy of this situation is the classic "two face / vase illusion"; this is the picture where you can look at it one way and see a vase, or you can look at it another way and see the profile of two faces pointing at each other.
Although tivra Ma is not acceptable as a secondary drone, it is acceptable as a tertiary drone. For instance if one were playing Marwa and there was already a drone of Sa, and Dha, then it would be quite acceptable to add a tivra Ma. The presence of the Dha against the Sa would keep the performance sufficiently grounded so that there would be no confusion from the addition of tivra Ma.
This page has gone over the drones of Indian music in some detail. At first, the drone may appear to be trivial, but it really is not. The drone is necessary to define the modality of the piece. Sometimes this is very simple. Other times, it requires a rather sophisticated understanding of the structure of the rag.
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