SYNTHESIZING A JAVANESE GONG AGENG
Lydia Ayers Andrew Horner
The Hong Kong University of Science & Technology
Department of Computer Science
Clear Water Bay, Kowloon
Hong Kong
ABSTRACT
This paper considers the spectral properties of a
Javanese Gong Ageng, the large gong used in gamelan
music to mark the end of each gong cycle. The gong
tone has about a dozen significant partials. The
amplitude modulation of this gong is a characteristic
part of its spectral evolution, and includes some
synchronized frequency modulation when multiple
components occur at nearly the same frequency. We
have developed an additive synthesis Csound
implementation for synthesizing the Gong Ageng. The
model produces a tone that is very similar to the
original.
1. INTRODUCTION
The Gong Ageng is the large bronze gong that marks
the end of each gong cycle in Indonesian music. Gongs. as large as 135 centimeters (54
inches) have been created in the
past, but gongs larger than about
i ' 80 centimeters (32 inches) are...es... rarely made now. The percent of
copper mixed with other metals
in the alloy varies, and iron is
S occasionally used if bronze isn't
available. Indonesian gongs
come in many sizes, but the
Gong Ageng is the largest and
deepest (see Figure 1). The
instrument has a very deep,
a distinctly pitched rumble that
sounds like thunder or the
Oolling waves of the sea.' Slight
differences in the opposite
halves of a gong can create
beating in the sound. People
have poetic descriptive images
for different speeds of beats,
Figure 1. comparing slow beats with
Gong Ageng. waves of water and faster beats
with Bima's laughter. (Bima is one of the Pandava
brothers from the Mahabarata epic.) The gong is
considered one of the most important instruments in
Javanese music. Even one missed gong tone can cause
great confusion among members of the
ensemble (Suryabrata 1987).
Previous work on modeling pitched percussion
instruments has primarily focused on simulating Western
and Chinese bells (Ma 1981, Rossing and Zhou 1989,
Kuttner 1990, Rossing 1994, Zheng 1994, Horner, Ayers
and Law 1997, Hibber 2003) and orchestral gongs
originally from Turkey and China (Risset 1969,
Chowning 1973, Harvey 1981). Our previous work
explored the tones of the Woodstock gamelan, a
tubulong instrument rather than a set of gongs (Horner
and Ayers 1999). The Indonesian gongs are relatively
unexplored by comparison, and the Gong Ageng has a
lower and more focused pitch than its Chinese and
Turkish counterparts.
Section 2 of this paper outlines the spectral properties of
the Gong Ageng and Section 3 gives an additive
synthesis model of the instrument, which is implemented
in Csound (Vercoe 1992).
2. SPECTRAL PROPERTIES OF THE GONG
AGENG
We analyzed a Gong Ageng that is part of Kyai Parijata,
a Javanese gamelan from the 19th Century (Heins 1969)
that is still used in weekly performances at the Nusantara
Museum in Delft, the Netherlands. Geert Jan van
Oldenborgh recorded 16-bit 44.1 kHz sample tones of
the gamelan instruments (van Oldenborgh 2002). The
fundamental frequency of the Gong Ageng is 44.5 Hertz.
We performed a phase vocoder spectral analysis on the
Gong Ageng to estimate the amplitudes and frequencies
of the partials. The phase vocoder uses a bank of
bandpass filters centered on the harmonics of an
(analysis frequency' (Dolson 1986, Beauchamp 1993).
Figure 2 shows a plot of frequency vs. time for the lower
components. The dark flat lines indicate partials with
significant strength. The partials at 44.5, 89, 133 and
260 Hz are at the first, second, third and sixth harmonics
respectively. However, some of the partials are not at
strict integer multiples of the fundamental. For example,
because the inharmonic partial at 74 Hz falls between
the first and second harmonics, the phase vocoder
program does not have a separate bin for it, and puts it
mostly into the bin of the second harmonic. Another
inharmonic partial at 120 Hz falls mostly into the bin of
the third harmonic. The five partials with the most
significant amplitudes are the second, first, sixth, third
and fifth, respectively. The fourth harmonic does not
seem to be significant. Some of the partials are fairly
close in frequency (e.g., components at 275 and 282 Hz).
We decided to combine the harmonic and inharmonic
partials that appear in the same harmonic bin into a
single harmonic partial. The combined partials were
originally close enough to beat together, and we have
