How does a tabla work?

A tabla is really two drums played together. The small one on the right is the dayan (“right”). Its shell is carved from one block of hard wood such as sheesham (Indian rosewood) and hollowed out. The big one on the left is the bayan (“left”), a bowl of copper, brass or steel, or sometimes clay.

The head is called the pudi, and it is made of goatskin in layers. An extra ring of skin round the edge is the kinar (or chanti). The open skin inside it is the maidan. In the middle sits the black syahi: dozens of thin layers of a paste made from iron filings, soot, cooked rice or flour and gum, each one rubbed smooth before the next. On the bayan the syahi sits off to one side.

The head is laced onto the drum by a braided leather ring, the gajra. Leather straps, the baddhi, run from the gajra down to a ring at the bottom and back up, many times round. On the dayan, eight wooden blocks, the gatta, sit under the straps for tuning. Each drum rests on a cloth cushion ring (chutta or indri) so it can be tilted.

Hit a stretched skin and it shakes in several patterns at once, called modes. In each one some lines stay perfectly still: nodal lines. They can be straight lines across the middle (diameters) or circles. A mode is named (m, n): m nodal diameters and n nodal circles, counting the rim.

For a string or a flute, the modes are neatly 1, 2, 3, 4 times the lowest note: harmonics, which our ears hear as one clear pitch (see PianoClear). A round drumhead is different. Its modes come from the zeros of Bessel functions, and they land at 1 : 1.59 : 2.14 : 2.30 : 2.65 : 2.92. These overtones are inharmonic: they don't line up, so the ear can't find a pitch and hears a thud.

Tighter skin rings higher: the frequency grows with the square root of the tension, f = j/(2πa) · √(T/σ), where a is the radius and σ the mass of each square metre of skin. (More on standing waves in Waves and resonance.)

Most drums give a thud. The dayan gives a note you can sing, and it is tuned to the song's home note, Sa. In 1920 C. V. Raman, with Sivakali Kumar, showed why in the journal Nature, and in 1934 he explained it in full in the Proceedings of the Indian Academy of Sciences.

The secret is the syahi. It adds a lot of mass in the middle of the skin, and it is thickest at the centre. The heavy centre slows down the modes that move it most, and leaves others alone. With the right weight and taper, the first nine modes crowd into five groups at 1 : 2 : 3 : 4 : 5: a proper harmonic series, just like a string's.

Raman matched each harmonic to its modes: (0,1) gives the first; (1,1) the second; (2,1) and (0,2) the third; (3,1) and (1,2) the fourth; and (4,1), (2,2) and (0,3) the fifth. The maker builds the syahi layer by layer and listens, rubbing and adding until the tone rings true.

Tabla players speak their rhythms as syllables called bols, and each bol is a way of striking. The trick is where one finger strikes and where another rests.

Na (or ta): the index finger flicks the kinar while the ring finger rests lightly on the edge of the syahi. Tin: the same, but struck on the open maidan. Tun: strike the centre and lift away. Te: fingers slap flat onto the syahi and stay, a dry click.

Why do they sound so different? A resting finger stops the skin moving there. The round modes, which move the whole ring round the syahi, are damped and the fundamental fades. The modes with nodal lines just turn so a line runs under the finger, and keep ringing. So na and tin sound bright, and tun, struck at the centre where only the round modes move, is deep and full.

On the bayan, ge (or ghe) is an open boom and ke (or ka) is a flat-hand slap that kills it. Play both hands together and you get the big bols: dha = na + ge, and dhin = tin + ge.

The big bayan gives the tabla its bass. Unlike the dayan, it isn't held to one fixed note. Its syahi sits off-centre, towards the player. The wrist and heel of the left hand rest at its edge, the fingers reach over to strike the open skin beyond, and the heel can press.

Pressing pushes the skin down and stretches it, so the tension goes up. A tighter skin vibrates faster. For any stretched skin or string, the frequency grows with the square root of the tension: f ∝ √T. Double the tension and the pitch rises by √2, about 41%, or six semitones.

So a good player strikes ge and then slides the heel forward while it rings: ghe-e-e, a boom that swoops up like a voice. This glide is called gamak (or meend), and it lets the bayan “talk”. A flat slap, ke, stops it dead.

Before a concert, the tabla player tunes the dayan to the song's home note, Sa. If the singer's Sa is C♯, the dayan must ring at C♯ too.

For big changes the player hammers the wooden gatta blocks down. Each gatta sits in a V of strap, and pushing it towards the narrow end pulls the straps tighter, which stretches the head. Then the player taps the gajra, the braided rim, with a small hammer: tapping it down tightens the head and raises the pitch, tapping it up from below loosens it. They go all the way round, so the head is tuned evenly.

Pitch goes with the square root of tension, f ∝ √T. One semitone is a pitch step of about 5.9%, so it needs about 12% more tension. A tap on the gajra moves the pitch by only a few cents (hundredths of a semitone).

Once tuned, the tabla keeps time. Teentaal is a cycle of 16 beats in four parts (vibhags). You clap on beats 1, 5 and 13 (tali) and wave on beat 9 (khali), where the bayan goes quiet. Beat 1, the sam, is where everyone lands together.