Abstract
This study considered the Sabah traditional bamboo musical instrument, sompoton. The fast Fourier transform (FFT) of sompoton was determined via a Pico oscilloscope. All three sompotons displayed almost similar fundamental frequencies. The individual tubes 1, 2, 3, 4, 5, 6, and 8 (except tube 7) of sompoton I, II, and III produced the fundamental frequency (in hertz) as 924, 758, 655, 589, 449, 407, 537, as 954, 779, 655, 614, 469, 387, 552, and as 944, 820, 655, 635, 407, 407, and 552, respectively. The averaged frequency obtained from the three sompotons (with the diatonic frequency and note in bracket) was 940.6 (932.3-A5# tube 1), 785.6 (783.9-G5 tube 2), 655 (659.2-E5 tube 3), 612.6 (622.2-D5# tube 4), 547 (554.3-C5# tube 8), 441.6 (440-A4 tube 5), and 400.3 (392-G4 tube 6). The tunings were remarkably similar in the tonal relationships. The pitch of the drone tube (tube 6) repeated an octave higher at tube 2, the intervals of perfect 4th higher at tube 8, and the intervals of perfect 5th higher at tube 4 were always found. The standard deviations of the fundamental pitch from the three sompotons for tube 1, 2, 3, 4, 5, 6, and 8 were 15.3, 31.5, 0.0, 9.2, 31.6, 11.5, and 8.7, respectively.
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Sompoton: Sabah Bamboo Mouth Organ
Sinin Hamdan,a Md Rezaur Rahman,a,* Khairul Anwar Mohamad Said,a Ana Sakura Zainal Abidin,a and Ahmad Fauzi Musib b
This study considered the Sabah traditional bamboo musical instrument, sompoton. The fast Fourier transform (FFT) of sompoton was determined via a Pico oscilloscope. All three sompotons displayed almost similar fundamental frequencies. The individual tubes 1, 2, 3, 4, 5, 6, and 8 (except tube 7) of sompoton I, II, and III produced the fundamental frequency (in hertz) as 924, 758, 655, 589, 449, 407, 537, as 954, 779, 655, 614, 469, 387, 552, and as 944, 820, 655, 635, 407, 407, and 552, respectively. The averaged frequency obtained from the three sompotons (with the diatonic frequency and note in bracket) was 940.6 (932.3-A5# tube 1), 785.6 (783.9-G5 tube 2), 655 (659.2-E5 tube 3), 612.6 (622.2-D5# tube 4), 547 (554.3-C5# tube 8), 441.6 (440-A4 tube 5), and 400.3 (392-G4 tube 6). The tunings were remarkably similar in the tonal relationships. The pitch of the drone tube (tube 6) repeated an octave higher at tube 2, the intervals of perfect 4th higher at tube 8, and the intervals of perfect 5th higher at tube 4 were always found. The standard deviations of the fundamental pitch from the three sompotons for tube 1, 2, 3, 4, 5, 6, and 8 were 15.3, 31.5, 0.0, 9.2, 31.6, 11.5, and 8.7, respectively.
DOI: 10.15376/biores.17.3.5335-5348
Keywords: Pitch; Fast Fourier transform (FFT); Fundamental frequency; Diatonic frequency; Tonal relationship
Contact information: a: Faculty of Engineering, Universiti Malaysia Sarawak, Kota Samarahan 94300 Sarawak, Malaysia; b: Department of Music, Universiti Putra Malaysia, Selangor 43400 Malaysia;
* Corresponding author: rmrezaur@unimas.my
INTRODUCTION
The sompoton is a mouth organ instrument found in Sabah, Malaysia. Though it is considered complicated, it is the most popular solo instrument. It is made from a gourd with bamboo tubes (Marasan 2003) and played especially in Sabah only (Frame 1982; Pugh-Kitingan 1992; Pugh-Kitingan 2000). The instrument consists of eight bamboo tubes (seven with a single free vibrating reed of palm bark set near the base of the tube) fitted together with a type of beeswax inside a hollowed gourd, which serves as the wind chest. Figure 1 shows the individual tubes, each with its own name such as tinangga (1), tuntutuk (2), rondom (3), baranat (4), monongkol (5), Gobou (6), lombohon (7), and suruk (8) (Marasan 2003). The lombohon does not produce sound and serves to balance the tube structure arrangement.
The tops of tubes 1, 2, 3, and 4 are covered with the second, third, fourth, and fifth fingers of the right hand to control the sounds. Tube 1 has holes at the top and bottom of the tube, while tube 5 has a hole at the bottom only, which is covered when the sound is needed (Fig. 2a). Tube 8 has a hole at the bottom, which is covered when the sound is needed (Fig. 2b). The normal method of holding the instrument is as follows, the gourd and lower part of the tubes are held in the left hand, which allows the thumb to control the holes at the bottom of tubes 1 and 5 while at the same time the second finger controls the hole at the bottom of tube 8. The second, third, fourth, and fifth fingers of the right hand are placed with their tips over the tops of tubes 1, 2, 3, and 4, which leaves the right-hand thumb free to control the hole located towards the top of tube 1. It should be noted that tube 1 has three methods of controlling the hole of the tube, that is, using the thumbs of both the right and left hands and the second finger of the right hand. Notes are selected by closing the holes at the bottom of the tubes 1 and 5 using the left-hand thumb (Fig. 2a) and closing the hole at the bottom of tube 8 with the left-hand second finger (Fig. 2b). Tube 6 with the lowest pitch sounds continuously as a drone. The tuning is a simple pentatonic scale, that is in A and gives the notes (low to high) E, F#, A, B, C#, E, F# (Missin 2016).
Fig. 1. The individual tubes: tinangga (1), tuntutuk (2), rondom (3), baranat (4), monongkol (5), Gobou (6), lombohon (7), and suruk (8) inserted in the gourd windchest
Fig. 2. (a) Tube 1 with the hole at the top and the base of the tube and tube 5 with the hole at the base only (b): Tube 8 with the hole at the base of the tube
The gourd used is classified botanically as Lagenaria sinceraria, or “bottle gourd” (Williams 1961). The suitable bamboo for the tubes is Schizostachyum pilosum locally known as lampaki. The stalks are cut into different lengths and dried. The bamboo tubes are bound together (four on one side) with a dried fern (Athyrium filix-femina (L.) Roth) and further secured by placing beeswax around and between the bases of the tubes. The fern stalk is cut, the skin peeled, and the strands from the inner side of the stalk taken and dried. These strands are split into fine strings and used as a string to tie the bamboo tubes together into a two layered raft. The beeswax is derived from a bee (Trigona bee, the largest genera of stingless bees and is used to seal the gaps between the bamboo tubes and the gourd. The reeds are cut directly from small palm (Arenga pinnata) lamellae. The bark of the palm tree is cut, and its skin peeled to make the vibrator. The vibrator does not have a fixed standard dimension to produce certain sound frequency and it depends on the expertise of the master crafter. The reeds are glued onto one end of the bamboo tube. Table 1 shows the materials for sompoton fabrication.
Table 1. Materials for Sompoton Fabrication 
The reed (vibrator) does not have a fixed standard dimension to produce certain sound frequency and it depends on the expertise of the master crafter. The maker’s intuition permits him to create a specific ‘signature’ through sound that is unique to a given sompoton. Figure 3 shows section A and B that is scraped to obtain lower and higher pitches, respectively (Saidal 2018). Figures 4 (a) and (b) show tubes 1, 2, 3, and 4 (left to right) and (b): Tubes 5, 6, 7, and 8 (right to left, with tube no. 7 reed less), respectively.
Fig. 3. The reed showing section A and B that is scraped to obtain lower and higher pitches, respectively (Saidal 2018)
The tuning is in a simple pentatonic scale that gives the notes (from low to high). The aim of the research was to identify the notes of the individual tube and determine the key to the instrument. This research stands out and is novel because not much research had been conducted to determine whether the finding is in accordance with previous studies that is in A major (Missin 2016), A# minor (Saidal 2018) and in C major (Wei and Dayou 2009). Wei and Dayou (2009) only studied the frequency characteristic of sound from sompoton musical instrument, whereas this study presented the musical key together with the 7 notes from the individual tubes.
Fig. 4. (a) Tubes 1, 2, 3, and 4 (left to right, length, L = 13cm) and (b) Tubes 5, (L = 19cm), 6 (L = 29cm), 7 (L = 29cm), and 8 (L = 26cm) (right to left) with tube no. 7 reed less. All tubes have similar diameter, D=11mm
MATERIALS AND METHODS
Figure 5 shows the 3 sompotons I, II, and III supplied by Kokoriu Enterprise, Kota Kinabalu, Sabah, Malaysia. The pitch of the individual tubes was determined via a Pico oscilloscope recording for both the time and frequency spectrum, which identified the fundamentals and overtones of the individual tubes using fast Fourier transform (FFT) analysis. Figure 6 shows the schematic diagram of the experimental setups in the laboratory at 25 °C and 60% relative humidity. The frequency of sound from each tube was determined by closing six tubes so that only the tube of interest produced sound. The frequency of each tube was collected in triplicate.
Fig. 5. Sompotons I, II, and III
Fig. 6. Schematic diagram of the experimental setups
The microphone was held above the top surface along the axis of symmetry at a distance of approximately 20 cm. In this study, the audio signal derived from the striking by an expert player was recorded. The audio signal was recorded in mono, at a 24-bit resolution and a 48 kHz sampling rate. The audio signal was recorded with the aid of a digital audio interface in a wave format. To ensure the recorded audio signal was at the optimum level, audio signal calibration of the recording system was completed. A test tone of a 1.0 kHz sine wave was used to calibrate the recording system. In this study, the ‘unity’ calibration level was at +4 dBu or -10 dBV and was read by the recording device as ‘0 VU’.
In this regard, the European broadcasting union (EBU) recommended the digital equivalent of 0 VU; i.e., the test tone generated for the recording device of the experimentation was recorded at -18 dBFS (Digital) or +4 dBu (Analog), which was equivalent to 0 VU. During this thorough calibration procedure, no device was unknowingly boosted, or its amplitude unknowingly attenuated in the signal chain at the time the recording was completed. The recording apparatus was an Audio-Technica AT4050 microphone (Audio-Technica Corp., Tokyo, Japan), XLR cable (balance), with the microphone position on an axis (less than 20 cm), and the microphone setting with low cut (flat) 0 dB. PicoScope computer software (Pico Technology, 3000 series, Eaton Socon, United Kingdom) was used to view and analyze the time signals from the PicoScope oscilloscopes (Pico Technology, 3000 series, Eaton Socon, United Kingdom) and data loggers for real time signal acquisition. The PicoScope software enables analysis using FFT, a spectrum analyzer, voltage-based triggers, and the ability to save/load waveforms to a disk. The amplifier (Behringer Powerplay Pro XL, Behringer, China) ensured that the sound capture was loud enough to be detected by the signal converter.
RESULTS AND DISCUSSION
Figure 7 shows a typical signal from the Pico oscilloscope recording both the voltage versus time (millisecond) signal (top) and intensity (dBu) versus frequency (kHz) spectrum (bottom) for tube 8 of sompoton I. The peaks in the spectrum are the fundamental (F0) and overtones (Fn) frequencies produced by the tube and these frequencies are summarize in Tables 2 to 4. From the three instruments examined, the tunings were remarkably similar in the tonal relationships between the seven pitches (from 7 tubes) as shown in Tables 2, 3 and 4.
Fig. 7. A typical signal from the Pico oscilloscope recording both the voltage (Volt) versus time (millisecond) signal (top) and intensity (dBu) versus frequency (kHz) spectrum (bottom).
Table 2. Fundamental (F0) and Overtones (Fn) Frequency (Hz) for Tubes 1 to 8 Obtained from Sompoton I
Table 3. Fundamental (F0) and Overtones (Fn) Frequency (Hz) for Tubes 1 to 8 Obtained from Sompoton II
Table 4. The Fundamental (F0) and Overtones (Fn) Frequency (Hz) for Tubes 1 to 8 Obtained from Sompoton III
Tables 5 and 6 show the average frequency (from 3 sompotons I, II, and III for tubes 1 to 8, except tube 7) and the corresponding standard deviations. The fundamental pitch of drone tube (with the diatonic frequency and note in the bracket) at 400.3 Hz (392 Hz-G4 from tube 6) is always repeated an octave higher at 785.6 Hz (783.9 Hz-G5 from tube 2), the intervals of the perfect 4th higher at 547 Hz (554.3 Hz-C5# from tube 8), and the intervals of the perfect 5th higher at 612.2 Hz (622.5 Hz-D5# from tube 4). Although the pitch relationships remained constant, the instruments varied slightly in pitch level due to the inaccuracy in fabricating the reed. The standard deviations of the fundamental pitch from the three sompotons for tubes 1 to 8 (except tube 7) are 15.3, 31.5, 0.0, 9.2, 31.6, 11.5, and 8.7, respectively. The deviation in the frequency was due to the disparity of the free vibrating reed at the end of the tube.
Table 5. Average Fundamental (F0) and Overtones (Fn) Frequency (Hz) for Tubes 1 to 8 Obtained from 3 Sompotons I, II, and III
Table 6. Standard Deviations of the Fundamental (F0) and Overtones (Fn) Pitch for Tubes 1 to 8 Obtained from 3 Sompotons I, II, and III
From Tables 2, 3 and 4, the Figs. 8, 9 and 10 were plotted to show the changes in frequencies from the first (F0) to the thirteenth (F12) harmonics for tubes 1 to 8 obtained from sompotons I, II, and III. The Fo denotes the first harmonics frequency for each tube. From Table 5, Fig. 11 was plotted to show the change in frequencies from the first harmonics to the thirteenth harmonics for tubes 1 to 8 obtained from the average values of 3 tubes from sompotons I, II and III. The pitch of the tube was not based on the open-end pipe principle (one end is closed), although Fig. 11 shows that the harmonic frequency is proportional to the harmonic number. It also does not follow the closed-end principle because the first four tubes have similar lengths but produce different frequencies. The different pitch is purely caused by the reed tuned by the master crafter.
Fig. 8. The change in frequencies from the first harmonics to the thirteenth harmonics for tubes 1 to 8 obtained from sompoton I