Published in Journal of ITC Sangeet Research Academy, Vol. 22 pp 13 – 22, December 2008
Developing a Tabla Playing Robot Prakash Persad*, Jorrel Bisnath* and Narvin Ramkissoon** *Mechatronics Group, University of Trinidad and Tobago Lots 74-98, O’Meara Industrial Park, Arima, Trinidad, W. I. Email:
[email protected] Email:
[email protected] Phone: 1-868-642-8888 ext 21060 **Industrial Plant Services Limited Caspian Drive, Point Lisas Industrial Estate, Couva, Trinidad & Tobago West Indies
This work describes the development of a biomimicking robot to play hand drums. The drum technique used by human players was analysed from which the design parameters were determined. A prototype was designed and programmed to play various rhythms. Keywords: Drumming Robot, Tabla, Biomimicking 1. INTRODUCTION
Robotics technology, once limited to industrial environments is now available for applications such as Honda’s ASIMO [1]. This type of integration has become commonplace, allowing for the acceptance of robotics in traditionally non-technological areas [11]. Music is one such area. It has been suggested that research in robotic-based music may be necessary to develop human-robot interactions, an important concern for the acceptance of robotics in non-industrial applications [4]. In music, the percussion instruments generally repeat a rhythm at a constant speed. As a rhythm is generated by a fixed sequence of movements
of the hands or fingers, it is thus ideally suited for robotic applications [3]. Most of the work reported on robotic drummers has been with single density drumheads, whose simplicity allows playing to be accomplished by simply striking the drum with a stick [2]. Such robots had to concentrate only on timing and speed as the instruments which were played were incapable of complex musical tones. The generation of more diverse musical sounds has only been accomplished by creating a device which would allow a controller to play multiple drums; each with a different tone [12]. No work has yet been reported on a robot which can play a more complex drum such as the tabla. Such a robot would have to use intricate finger strokes of both hands [8] in order to extract the full range of tonal sounds from the instrument [7]. 2.
PLAYING THE TABLA
The tabla consists of two hand drums, which are played simultaneously using both hands. The smaller drum, called the dayan is used for treble notes, while the larger drum, called the bayan
Published in Journal of ITC Sangeet Research Academy, Vol. 22 pp 13 – 22, December 2008
produces the deeper bass notes. The drumhead or puri of the tabla consists of three major parts, the maidan, the chat and the syahi as shown in Figure 1. The maidan is the only membrane which covers the entire face of the drum. It is usually made of high to medium grade leather. The chat is a circular membrane of low grade leather that runs around the outer edge of the drumhead, striking it produces a higher resonating sound. The syahi is the black spot at the centre of the tabla and is a mixture of gum, soot, and iron filings. The syahi is mainly responsible for creating the harmonics of the drum.
Figure 1. The parts
of the tabla Drumhead [8]
The tabla is a unique and complex instrument. It follows then that there is a unique and complicated method to playing it. Before playing the drums however, a basic understanding of the structure of Indian music is necessary. The fundamental unit of sound is the bol, the western equivalent of a beat. This may be the sound produced by striking the drum with one or more fingers. The various notes all have specific names, which are similar in sound to what is being played. On the Bayan, Ge and Ke are common notes, while the Dayan has Na, Tin, Tun, Ti and Ta. Examples of combinational notes include Dha (Na and Ge) and Dhin (Tin
and Ge). Since compositions were often taught from masters to students orally, the labelling of the notes in this manner allowed the music to be taught via song. The notes themselves were created by striking the two drumheads in a specific position or manner as described in Table 1.
Bol
Manner of playing
Na
Dayan: Index finger strikes chat. Third finger damps the fundamental by resting on head.
Tun
Dayan: Index finger strikes syahi; no damping.
Ke
Bayan: Damped stroke played with flat hand across all surfaces.
Ge
Bayan: Tip in middle finger strikes the far side of the syahi. Heel of hand, on maidan, can alter pitch.
Ti /Tin
Dayan: Damped stroke: middle and index fingers strike syahi in rapid succession, and remain on drum.
Ta
Dayan: Index finger strikes edge of chat. Third finger damps fundamental by resting on head. Similar to Na
Dha
Simultaneous striking of Na and Ge.
Dhin
Simultaneous striking of Tin and Ge
Table 1 Various
notes of the tabla [7, 8]
Using these notes, rhythms could then be developed. These rhythms also known as Taals are similar to western music in their rhythmic structure in that they are both grouped in measures e.g. 4/4, while not being limited to set count e.g. 3/2/3. Over the years however, a few main rhythms have been accepted as
Published in Journal of ITC Sangeet Research Academy, Vol. 22 pp 13 – 22, December 2008
conventional such as Bhajan Teka (an 8 beat rhythm), Rupak Taal (a 7 beat rhythm), Teen Taal (a 16 beat rhythm), Dadra Taal (a 6 beat rhythm) and Keharwa Taal (an 8 beat rhythm).
The middle finger is free to strike the black spot. The wrist and knuckle are kept straight when striking the drum, acting as one during the stroke.
The prototype was therefore designed to play the basic rhythms from the various notes just as a drummer would.
3. DESIGN OF A PROTOTYPE Figure 2. A
Several factors must be considered in the design of a bio-mimicking device. The first of which is an understanding of what is being modelled. In this case, it is a professional tabla player
3.1 Analysis of human drummer The basic posture can be seen from Figure 2. The player usually sits on the floor with legs crossed with a straight back. The shoulders are relaxed and level. The larger bass drum is usually played with the left hand. The player usually keeps this drum straight so that the drumhead is parallel to the floor. The forearm of the left hand is almost parallel with the skin of the drum, with heel of the hand being placed on the membrane just before the black spot. This hand always remains on the membrane when playing. The notes are played by striking the membrane on the other side of the spot. The smaller wooden drum is most often played with the right hand. It is normally tilted forward and to the left at an angle of approximately 30 degrees. The index finger is placed to strike either the outer skin or the inner membrane; with the ring and little finger are positioned 90 degrees counter-clockwise to the index finger.
trained tabla player.
3.2 Supports Tablas are manufactured at different sizes for different scales and pitches of the notes. As a result the robot should be capable of adjusting to the required height and fastened in that position. As shown in Figure 4, the supports which the hands are mounted upon are capable of being adjusted to different heights for different sizes of drums; the right hand and the left hand are isolated from the common support. The shoulders themselves are placed 13” apart and approximately 16” above the base. The shoulder of the robotic arm may be rotated 180 degrees around a vertical axis and is capable of adjusting the height of the arm within a 3” range and being fixed into any desired position, to allow for any small variations in the sizes of tablas. 3.3 Arms On observing a professional tabla player, it is noted that both hands are positioned at different places on the tabla to obtain the different notes. Hence the hands must be fixed in such a way so as to allow for this positioning on the different drums. This means that the design must cater for
Published in Journal of ITC Sangeet Research Academy, Vol. 22 pp 13 – 22, December 2008
adjustability in the horizontal plane as well as in the vertical plane. As can be seen in Figure 2, the treble drums are never played in a 90 degree position. The basic reason is for the comfort of the musician and the second is derived from the fact that proper playing technique requires that the wrist remain in line with the forearm. This limitation makes it difficult for a drummer to generate the required force to produce a powerful note. To overcome this, the musician tilts the drums forward (approximately 30 degrees to the horizontal plane). To allow this and other fine adjustments in the prototype, the arms were constructed to allow adjustability at areas synonymous to the human arm demonstrated by Figures 2 and 4.
steel tubing, rubber, polyethylene rod, wood, hosing and PVC of varying diameters, were each tested to determine which would best produce a tone comparable to that of a human. A test finger was fashioned out of each material and allowed to strike the drum. An expert player then decided which sound was the most similar to his own.
Figure 4. Prototype Robot
6”
Figure 3. The range of motion
9”
of robotic hands
The right hand was allowed a maximum reach of 9”, while the left was left at 6” (see Figure 3). This was done to allow for the difference in size of the two drums. Both arms could also be adjusted to play anywhere within their maximum reach to allow for varied positioning of the tabla. 3.4 Hands The tabla being an intricate instrument requires accurate fingering technique for proper execution of the sound. The human finger is quite complex in nature thus the texture and force requirements of the material must be considered for the material selection of the prototype’s finger. Materials, including mild
The free body diagram of the test finger is shown in Figure 5; F1 and F3 are due to actuation, F2 is the normal force of the pivot, F4 is the weight of the material, and F5 results from striking the drum. Using the speed which the fingers would be travelling at while playing, these forces were then calculated and used in the design of the finger and sizing of the actuator.
F1
F2
F3
F4
Figure 5. Free body diagram
F5
for test finger.
The most suitable materials were then screened by their individual properties, with the final choice being based on the structural soundness, weight, noise control and ease of fabrication characteristics.
Published in Journal of ITC Sangeet Research Academy, Vol. 22 pp 13 – 22, December 2008
On the Dayan, three fingers were used. As demonstrated in Figure 6, the first is positioned to strike the chat and play the note, Na. The next was placed to strike the syahi, producing the note, Ti. In addition to these two, the tenor side of the tabla needs to be damped to create the various overtones from the membranes. A third finger was therefore incorporated into the design to accomplish this.
4. PROGRAMMING AND TESTING OF PROTOTYPE
A programmable logic controller (PLC) was chosen as the controller, as it allows for a fast development time and has a programming syntax which is easier to troubleshoot than most other systems.
Relay Circuit
Controller
Figure 7. Illustration
Actuator Circuit
of Controller
Implementation
Figure 6. The prototype
created with the tabla.
The fingers for the bass drum are fabricated out of the same material. These fingers, however, are positioned differently on the drum as observed from the human hand. To create the note, Ka, two fingers had to be joined and bent to allow for a flat stroke on the syahi. Rubber again had to be used to cushion the blow and create the proper sound. The note, Ge required that the finger be bent in the opposite direction, as in playing the note, only the tip of the finger is allowed to strike the drum. The fingers and actuators were housed in each hand, with a case was placed over the entire assembly to make the set up more appealing and to reduce the amount of noise generated by the components.
A simple relay circuit was used as an intermediary as shown in Figure 7 to allow the PLC to control the actuation. An open looped control system was sufficient for initial operation. As with all music, timing is critical to rhythm. Slight variations in timing between different instruments destroy the harmony of an orchestra. In this regard, proper control of the prototype would rely on an accurate understanding of the timing influences. Ts Tc
Ta Te
Figure 8.
Controller timing diagram.
As shown in Figure 8, there are three major influences on the execution process. The scan time, Ts is the time taken for the controller to read the instructions. This time on average per execution was 0.12ms. The time taken for the
Published in Journal of ITC Sangeet Research Academy, Vol. 22 pp 13 – 22, December 2008
controller to act on the instructions, Tc was 10ms. The final influence was the time take for actuation, Ta. This time varied for each of the notes being played. The longest of these times was for the note Ge, which was 19ms. This information could now be integrated into the timing of the prototype. In order to keep the program stable, the recommended ratio of Ts + Tc + Ta : Te should be 1:10 The time that was eventually allocated for the execution, Te was 120ms. This period was chosen as a compromise between the ratio above and the time limitations of associated with the spacing of the beats in the pieces of music to be
Figure 9. Timing diagram
played. An example of the resulting timing of the prototype is shown in Figure 9. Diagrams similar to this were then created for the various beats which the prototype would have to perform. The timing diagrams could then be used to program some of the more common beats. On completion of programming, limited testing was done on the sound produced. While the prototype is still rudimentary, the sound quality was comparable to a professional. Analysis of sound generated confirmed this, as both had similar wave profiles. A preliminary survey also revealed that most non-experts could not differentiate between the prototype and a professional.
for an 8 beat rhythm (Bhajan Theka).
Published in Journal of ITC Sangeet Research Academy, Vol. 22 pp 13 – 22, December 2008
5. CONCLUSION The prototype machine has taken a totally different approach to reproducing the sound of a professional tabla player. In so doing, it has shown itself to be a viable system for accurately recreating the desired sound. While the number of notes which the prototype is capable of playing is still limited, it has shown that it can produce the required rhythms to an acceptable standard. In developing the prototype, several other applications also became apparent. At present, most people learn to play the tabla on a one on one basis, teachers are hard to come by and lessons are expensive. There are very few written works on playing the tabla and most of the time the various rhythms are learnt orally. A machine such as this may be used as a teaching aid or a personal tutor for learning the tabla. Applications may also include replaying musical archives in museums and similar institutions. REFERENCES 1. Honda 2005. Honda Debuts New ASIMO http://world.honda.com/news/2005/c051 213.html 2. Kapur, Ajay “A HISTORY OF ROBOTIC MUSICAL INSTRUMENTS” Proceedings of the 2005 International Computer Music Conference 2005. 3. Weinberg, G. and Driscoll, S. “RobotHuman Interaction with an Anthropomorphic Percussionist.” in International ACM Computer Human Interaction Conference 2006. Montreal, Canada. 4. Crick, C. and Munz, M. and Nad, T. and Scassellati, B. “Robotic drumming: synchronization in social tasks.” 15th
IEEE International Symposium on Robot and Human Interactive Communication 2006. Hatfield, United Kingdom. 5. Malu, S.S. and Siddharthan, A. “Acoustics of the Indian Drum” arXiv:math-ph/0001030 v1 20 Available at http://arxviv.org Jan 2000 6. Patel, Aniruddh D. and Iversen, John R. “Acoustic and Perceptual Comparison of Speech and Drum Sounds in the North Indian tabla Tradition: An Empirical Study of Sound Symbolism” Proceedings of the 15th International Congress of Phonetic Sciences, 3-9 August 2003, Barcelona. 7. Reddy, Ananth T. MD “TABLA PRIMER FOR THE OLDER STUDENT” originally published in the ATA Fourth Annual Conference magazine 1996. Available at http://www.chandrakantha.com/tablasite/ articles/tablaprimer.htm 8. Courtney, David R. “BASIC STROKES AND BOLS” adapted from Fundamentals of tabla: Complete Reference for tabla vol. 1. Available at http://www.chandrakantha.com/tablasite/ bsicbols.htm#Dha 9. *Ramkissoon, Narvin A. “DESIGN AND BUILD A ROBOT TO PLAY THE TABLA” (Final Year Undergraduate Thesis, department of Mechanical and Manufacturing Eng. University of the West Indies 2006) 10. Pathak, Ajeet - eminent tabla player. Available at http://www.nupurdanceacademy.com/10 89.html 11. Jennings, Craig. President Motoman, Inc. (January 2001). Automation Advances Expand Robot Applications. Modern Application News. Available at http://www.manufacturingcenter.com/ma
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n/articles/ArchiveWrapper.asp?article=m 0101mp.htm 12. Kapur, A., Singer, E., Benning, M. S., Tzanetakis,G., Trimpin, “INTEGRATING HYPERINSTRUMENTS, MUSICAL ROBOTS & MACHINE MUSICIANSHIP FOR NORTH INDIAN CLASSICAL MUSIC” Proceedings of the 2007 Conference on New Interfaces for Musical Expression (NIME07), New York, NY, USA.
AUTHOR RESUMÉS Prakash Persad is a Professor of Mechatronics and an acting Vice Provost at the University of Trinidad and Tobago. He is also a practicing pundit and tabla player. His research interests include; robotics, robotic applications and artificial intelligence. He has published in both the fields of engineering and religion. Narvin Ramkissoon is a Bsc. honours graduate of mechanical engineering from the University of the West Indies and an accomplished dholak player. He is currently a practicing mechanical engineer at Industrial Plant Services Limited in Trinidad and Tobago. Jorrel Bisnath is a Bsc honours graduate of mechanical engineering from the University of the West Indies. He is a research assistant at the University of Trinidad and Tobago in the field of mechatronics, and is currently involved with robotics research.
