Proceeding of International Conference On Research, Implementation And Education Of Mathematics And Sciences 2014, Yogyakarta State University, 18-20 May 2014

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ANALYSISAND SYNTHESIS OF SOUND OF GONGAGENG OF KAGUNGAN DALEM GONGSO KANJENG KYAI GUNTUR SARI

Ahmad Fauji, Agus Purwanto
Vibration and Wave Laboratory , Physics Departement, Faculty of Mathematics and Science, Yogyakarta State University

Abstract

The purpose of this research was to analyze the sound of the Gong Ageng of Kagungan Dalem Gongso Kanjeng Kyai Guntur Sari. Based on the result of the analysis it was then synthesized a new signal to comprehend whether the analysis results were appropriate or not .
The research was conducted by recording the sound of the gong by using Sound Forge software. The data of recording result were analyzed using FFT in order to obtain the sound signal components. The process of sound synthesis was conducted by using additive synthesis method supported by Matlab (R2012a) sofware.
The results of this study showed that there were some basic factors which determined sound signal, which were fundamental frequency, harmonic frequencies, amplitudes, amplitude ratios and phase differences. The sound signal as the result of reconstruction from the data had been close enough to natural sound produced by the gong.
The results of this study showed that the phenomenon of "ngombak" on the gong ageng was a beat between two frequencies that have a relatively high amplitude. Beside that, this study also showed that there were some fundamental factors that made up a sound signal that were the fundamental frequency, harmonic frequencies, amplitudes, amplitude ratios and phase differences. The sound signal reconstructed from the data above was good enough to approach the natural sound generated by the gong.

Keywords : signals , ngombak, FFT , frequency , amplitude , and damping factors.

INTRODUCTION

Gamelan is a legacy left by ancestors of the world, especially for Indonesia. She was created hundreds of years ago from cultures of noble society. In manufacturing,the gamelan was done manually by the hand of a master. It was designed as an instrument to be used together. To determine the quality of her voice, a master relied on feelings and hearing acuity. So gamelan from one master is different to the other masters and the consequently there are not standard frequency on gamelan. When one piece of the gamelan is damaged it can not necessarily be replaced with a new device, as on western musical instruments.
The tone system of gamelan doesn‟t follow tone system of western music, gamelan has own tone system. For Javanese gamelan there are 2 different tone systems, that are laras slendro and laras pelog. Laras slendro has five tones which consists of barang (1), gulu (2), dada (3), lima (5), and nem (6), while laras pelog has seven tones which consists of barang alit (7=1), gulu (2), dada (3), pelog (4), lima (5), nem (6) and barang (7). Parts of Javanese gamelan in

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Ahmad Fauji, Agus Purwanto / Analysis And Synthesis…	ISBN 978 – 979 – 99314 – 8 – 1

general are as follows :

(a) Kendang (b) Gong (c) Kethuk
(d) Gambang

(e) Kempul (f) Siter
(g) Bonang (h) Gender

(j) Balungan (k) Kenong (i) Seruling
(l) Rebab.

(Prasetiyo, 2009:F-242)

The example of gamelan which uses laras pelog is Kagungan Dalem Gongso Kanjeng Kyai Guntur Sari. This gamelan is used only during the celebration of Sekaten at Yogyakarta Palace. Some of the constituent instruments are as follows :

(a) Gong ageng (b) Kempul
(c) Bende (d) Kethuk

(e) Kenong (f) Kepyang
(g) Saron demung (h) Saron ricik

(i) Bonang barung
(j) Bonang panembung (k) Bonang panerus
(l) Gender barung

Kagungan Dalem Gongso Kanjeng Kyai Guntur Sari has two gong ageng, that are gong ageng 1 and gong ageng 2. As in the case with the other gongs, gong ageng of Kagungan Dalem Gongso Kanjeng Kyai Guntur Sari also showed ngombak phenomenon. This phenomenon is typical of gong instruments.

RESEARCH METHOD

A. Time and Research Location.
This study was conducted from January 2013 to January 2014. Process of research was carried out at the Laboratory of Vibrations and Waves, Physics Department, Faculty of Mathematics and Science, Yogyakarta State University.

B. Research Object.
The object of this study was a recorded sound signal of gong ageng of Kagungan Dalem Gongso Kyai Guntur Sari Kanjeng obtained using Sound Forge 10.0 through a condensing microphone. The recording process started when the gong began sounding until it was fully damped.

C. Research Procedure.
The sampling process was done by hitting the gong one by one. The method of the hitting greatly affects the produced sound. The wrong technique will worsen the sample quality. To minimize error, gong hitting was performed by abdi dalem Kraton Yogyakarta.
The signals of gongs were analyzed by using Fast Fourier Transform (FFT) algorithm. FFT would produce Fourier coefficient, then the coefficient will determine the audio information of the gong. This audio information included fundamental frequency, harmonic frequencies, amplitudes, amplitude ratios and phase differences.
The process of sound synthesis was conducted by using additive synthesis method in Matlab (R2012a). Basically, this method made used some sinusoidal signal with the audio information. These signals “summarized” into a new signal.

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Proceeding of International Conference On Research, Implementation And Education Of Mathematics And Sciences 2014, Yogyakarta State University, 18-20 May 2014

D. Analysis
The FFT program was used to determine the value of the Fourier coefficients of the synthesized signal. Then the value of the Fourier coefficients was plotted against the frequency and the spectrum of the signal synthesis was obtained. This step was also conducted to the original signal. Having obtained the spectrum of the two signals, both frequencies would be compared to see the similarities.

RESULTAND DISCUSSION

1. Analysis of Sound of Gong Ageng

Gong Ageng of Kagungan Dalem Kanjeng Kyai Guntur Sari was the most unique instrument compared to the other gamelan instruments. One of the unique characteristics of this instrument was that when we made sound from it, a 'ngombak' phenomena would appear. Gong Ageng also had many frequency components. For example, gong ageng 1 had 19 frequency components while gong ageng 2 had 25 frequency components.
Frequency component was an indicator to show high or low tone. Meanwhile, the amplitude ratios would form the character of the instrument. The value of each frequency and amplitude ratio of each gong ageng 1 and gong ageng 2 were shown in Table 1 and 2:

Table 1. Amplitude ratio of original signal and synthesised signal of gong ageng 1
gong ageng 1
	
Original signal
	Synthesised signal

frequency
	
amplitude
	Amplitude ratios
	
frequency
	
amplitude
	Amplitude ratios
	
43.5855
	290.4801
	1
	43.7325
	527.4521
	1
	
56.0805
	36.65965
	0.126204
	56.0805
	58.75904
	0.083376
	
74.823
	125.1573
	0.430863
	75.0435
	63.56079
	0.101252
	
87.024
	518.1308
	1.783705
	87.3915
	877.6771
	1.475133
	
88.935
	2180.313
	7.505895
	89.5965
	1427.338
	1.557832
	
118.1145
	28.31888
	0.09749
	117.8205
	13.38962
	0.071566
	
123.921
	9.057939
	0.031183
	124.4355
	30.39211
	0.031546
	
130.389
	80.83877
	0.278294
	130.6095
	19.1658
	0.255322
	
132.3735
	27.38403
	0.094272
	132.8145
	54.74992
	0.25263
	
137.3715
	10.29893
	0.035455
	137.2245
	9.862239
	0.026247
	
167.433
	5.359279
	0.01845
	168.0945
	0.367681
	0.013309
	
175.812
	20.61247
	0.07096
	176.4735
	25.18157
	0.006505
	
210.945
	0.530349
	0.001826
	211.3125
	3.398372
	0.00733
	
219.324
	20.33095
	0.069991
	219.618
	11.6423
	0.01592
	
263.3505
	7.85345
	0.027036
	263.7915
	8.727534
	0.009102
	
289.2225
	4.055232
	0.01396
	289.8105
	3.824754
	0.009708
	
313.551
	3.385409
	0.011655
	314.2125
	1.568037
	0.007434
	
438.207
	1.793958
	0.006176
	438.942
	0.598541
	0.000504
	
473.4135
	1.459042
	0.005023
	473.7075
	0.574326
	0.001469

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Ahmad Fauji, Agus Purwanto / Analysis And Synthesis…	ISBN 978 – 979 – 99314 – 8 – 1

Table 2. Amplitude ratio of original signal and synthesised signal of gong ageng 2

gong ageng 2
	
original sinyal
	synthesised signal

frekuency
	
amplitude
	Amplitude ratios
	
frekuency
	
amplitude
	Amplitude ratios
	
44.1735
	5962.726
	1
	44.541
	10463.37
	1
	
46.3785
	198.217
	0.033243
	47.334
	394.4747
	0.045556
	
86.436
	1751.044
	0.293665
	87.0975
	2860.079
	0.31604
	
88.4205
	7516.638
	1.260604
	89.082
	11579.35
	1.133936
	
112.749
	92.33667
	0.015486
	113.1165
	152.0908
	0.015966
	
116.277
	266.1557
	0.044637
	116.718
	554.5294
	0.044927
	
122.9655
	328.7499
	0.055134
	123.5535
	412.2839
	0.028246
	
125.7585
	82.62618
	0.013857
	125.979
	131.8121
	0.02124
	
130.7565
	121.3184
	0.020346
	131.1975
	151.8596
	0.011546
	
132.8145
	111.0788
	0.018629
	133.182
	107.3699
	0.047408
	
136.857
	11.44797
	0.00192
	135.975
	29.88022
	0.00398
	
172.7985
	41.44363
	0.00695
	173.2395
	31.16096
	0.024869
	
175.0035
	218.2164
	0.036597
	175.2975
	203.469
	0.041182
	
177.135
	82.3277
	0.013807
	177.7965
	39.32614
	0.029877
	
219.177
	27.29256
	0.004577
	219.3975
	20.11249
	0.009358
	
243.138
	59.57948
	0.009992
	243.432
	83.94558
	0.004835
	
247.254
	53.8905
	0.009038
	247.401
	57.36946
	0.006856
	
263.3505
	7.85345
	0.001317
	263.865
	8.743175
	0.00151
	
278.7855
	153.0832
	0.025673
	279.153
	96.38983
	0.059328
	
287.3115
	31.44165
	0.005273
	287.8995
	25.03892
	0.01133
	
311.64
	12.72116
	0.002133
	311.934
	15.52344
	0.006634
	
392.343
	9.417998
	0.001579
	393.0045
	12.16339
	0.004984
	
408.807
	18.41672
	0.003089
	409.0275
	18.07803
	0.006274
	
419.4645
	13.06921
	0.002192
	419.832
	5.234486
	0.005602
	
458.346
	6.886629
	0.001155
	458.64
	5.554219
	0.003447

The tables show that gong ageng 1 and gong ageng 2 have similiar fundamental frequencies, i.e. 43.5855 and 44.1735. The first table show that the harmonic frequencies for the gong ageng 1 were 43.5855, 87.024, 130.389, 175.812, 219.324 dan 263.3505 Hz. While in the second table, the gong ageng 2 had values 44.1735, 88.4205, 132.8145, 177.135 Hz.
Gong ageng 1 and gong ageng 2 would produce „ngombak‟ phenomena if hitted. This happened because both frequency produced beat phenomena. The value of frequencies were 87.024 and 88.935 Hz for gong ageng 1 and frequencies for gong ageng 2 were 86.436 and 88.4205 Hz.

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Proceeding of International Conference On Research, Implementation And Education Of Mathematics And Sciences 2014, Yogyakarta State University, 18-20 May 2014

2. Synthesis of Sound of Gong Ageng

Having obtained the audio information of each gong, then we checked wheter the audio information was correct or not. One of the method to check was signal synthesis. First the new signal was should be synthesized. Then, the spectrum should be obtained. After that we compared the authentic signal with the synthetic signal.
In this experiment, the spectrum of original signal and synthesis signal were shown in the figure below.

Figure 1. Spectrum of original signal and synthesis signal of gong ageng 1

Figure 2. Spectrum of original signal and synthesis signal of gong ageng 2

The figure showed that the spectrum of synthetic signal was similiar to the authentic one. That facts showed that the frequency component and amplitude ratio were matching.

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Ahmad Fauji, Agus Purwanto / Analysis And Synthesis…	ISBN 978 – 979 – 99314 – 8 – 1

CONCLUSIONAND SUGGESTION

The harmonic frequencies appeared in the gong ageng 1 and gong ageng 2. The harmonic frequencies of each gong was 43.5855, 87.024, 130.389, 175.812, 219.324, 263.3505 and 44.1735, 88.4205, 132.8145, 177.135 Hz. The “ngombak” phenomena in both gong ageng was caused by similiar (close enough) frequencies with relatively high amplitude

REFERENCES

	Kahrs, Mark & Karlheinz Bradenburg. (2002). Applications of Digital Signal Processing to Audio and Acoustics. NewYork: Kluwer Academic Publishers.
	Nugraha, Ary., Sumarna & Agus Purwanto.(2006). Analisis Frekuensi dan pola Dasar Frekuensi Gender Laras Slendro.Prosiding, Seminar Nasional MIPA.Yogyakarta: FMIPA UNY.
	Prasetiyo, Agus Eko., Agus Purwanto, &Sumarna. (2009). Pola Rasio Amplitudo Komponen Harmonik Gender Barung Laras Slendro. Prosiding, Seminar Nasional Penelitian, Pendidikan, dan penerapan MIPA. Yogyakarta: FMIPA UNY.
	Surjodiningrat, W., P. J. Sudarjono, & Adhi Susanto. (1969). Penjelidikan dalam Pengukuran Nada Gamelan Djawa Terkemuka di Jogjakarta dan Surakarta. Jogjakarta: Laboratorium Akustik FT UGM.
	Tan, Li. (2008). Digital Signal Processing Fundamentals and Applications. San Francisco: Elsevier.

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