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Mridangam is characterized by a rich and varied tone. Some strokes evoke clear
pitched sounds while others evoke unpitched sounds. The following discussion is based upon
the pitched strokes because they more clearly show the tonal differences.
The size of the mridangam is one of the important factor for the sound it produces. The
pitch of the mridangam varies according to its size. The larger (Fig.1a) the mridangam,
the lower the pitch and the smaller (Fig.1b) the mridangam, the higher the pitch.
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Rim Stroke (right hand) - The rim stroke is a major stroke on the
mridangam. Although the nomenclature varies, this stroke is usually called "Na"
in the North and "Nam" in the South. On mridangam a predominant third harmonic
is the main characteristic (Fig. 2 a, b; below). However, the fundamental may be seen in
significant proportion in the mridangam while it is essentially absent in the tabla.
Furthermore the second harmonic tends to be evoked in the tabla while it is suppressed in
the mridangam.
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Open stroke (right hand) - The open stroke is also a major stroke for both drums. This is
called "Tun" in the North and "Dheem" in the South. Both strokes are
characterized by a very prominent fundamental. However there is a significant difference
in the second harmonic (Fig. 2 c,d).
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Open stroke (left hand) - The open stroke of the left hand is called "Ga" in the
North and "Thom" in the South. It shows a tremendous difference between the two
instruments (fig. 2 e,f). It has been found that the tabla has a very pronounced
fundamental and a long sustain. There are much fewer harmonics in this stroke. Conversely
the mridangam has a much more complex harmonic spectrum and a significantly reduced
sustain.
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In order to know the physical and structural relation of the type of skin used in making
the instrument and the sound produced, the cross sectional features of leather used in
different instruments were studied. In various skins horizontal fibres running
predominantly along the scales direction and the network structure flows perpendicular to
the scales direction.
In goat skins, there is no horizontal running of fibre bundles and the fibres is in loose
weaving. In sheep skin, the grain layer is comparatively larger than that of goat skin and
fine fibres predominantly running along the hair follicles direction. The cross sections
are plain and compact in cow calf leather. The fibres are glued together and from seperate
blocks in all directions.
The theory of circular membranes considers them as two dimensional stretched strings. The
fundamental frequency can be related as :
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fo1 = 0.382 T
R õ
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where,
fo1 = fundamental frequency
R = radius of the membranes
T = circumferential tension/unit length
(õ) = mass/unit area of the membrane
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The pitch of the membrane, as in a stretched string depends on the size and weight of the
membrane and the amount of tension it is under. The pitch lowers, as the size or weight is
increased and rises when the tension is increased. In the case of drums, the sound
produced by it depends on the resonator column and the properties of leather, the loudness
depends on the amplitude, energy and the intensity.
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