Research and reconstruction of art andacoustic cultural heritage by means of
optical methods
Toshimitsu ASAKURA

Recent advances in science and technology have brought about a diverse range of
methods for the scientific research of cultural
heritage, and significant developments arebeing made with all of these methods. This
paper introduces the recent research trends
in the use of optical methods (a type of scientific research method) for the research andreconstruction of visual and audio artifacts.
Particular attention is given to visual artifacts
in the form of paintings and sculptures, andaudio artifacts in the form of wax cylinder
records. As further developments are madein information technology, it is expectedthat museums and art galleries will compile
multimedia databases from a wide range ofcultural heritage resources, and optical techniques are likely to play a crucial role in thisactivity.
Keywords: cultural heritage, museum,art research, reconstruction
and reservation, scientific optical method, art and acoustic information, drawing andpainting materials, wax cylinder, disk record, multimedia
database

1. Introduction
Cultural heritage is generally classified
into “tangible cultural heritage” such as
paintings, sculptures, craftworks and historical documents, and “intangible cultural heritage” such as Kabuki, Noh and music. Tangible cultural heritage includes archaeologicaldocuments, the research of which may also
include excavation work. Cultural heritageis thus a wide-ranging field, both in termsof its temporal and geographical scale andin terms of the many different types of tangible and intangible objects included within
its definition. Consequently, there are also
many different ways in which cultural heritage can be researched and reconstructed.

It is therefore difficult to present a comprehensive treatment of the research and reconstruction of all types of cultural heritage. This
paper therefore concentrates on tangible cultural heritage that contains visual information(such as paintings, photographs and moving pictures), and intangible cultural heritagethat contains audio information (such as spoken language and folk music). Archaeologicalcultural heritage will not be considered here.
Research into cultural heritage has longsince been performed by intuitive methods
based on human sensitivity and methods
based on historical documents, whereas theintroduction of scientific methods only began
in the late 18th century. Scientific methods
were originally used for the analysis of ancient Greek and Roman coins and the microscopic and microchemical analysis of items
such as paintings. In the early 19th century,
museums and art galleries in Europe and theUnited States started to establish their own
laboratories for scientific research. Of particular note is the establishment in 1931 of
the Louvre Science Laboratory for museums
in France. After that, the research of cultural heritage by scientific methods became
firmly established, and scientific laboratories became permanent fixtures in museums
and art galleries throughout Europe and the
U.S. However, these scientific laboratories
were invariably used for research associated with visual information such as painting,sculptures and craftworks and were hardly
involved in any research aimed at cultural
heritage relating to audio information, which
was only performed at a handful of museumsin Europe and the U.S.
Meanwhile, in Japan-despite the interest
shown by a few people into scientific methods-it was only from the 1950s that scientific methods were specifically introduced
into the study of cultural heritage. Today,
research laboratories that use scientific meth-ods to work on cultural heritage are also permanent fixtures at Japanese museums andart galleries. However, there still do not appear to be any places doing substantial workon cultural heritage relating to audio information.
Recent advances in information technology have revolutionized the research of cultural heritage relating to visual and audio information in museums and art galleries. This
has led to developments such as the compilation of databases from all kinds of visual andaudio resources, the use of image processing
for the measurement and research of artifacts, and new display methods. As a result,cultural heritage is now becoming accessible
to (and is receiving greater interest from) the
wider public rather than just a handful of researchers.
As a research representative funded by
the Ministry of Education, Science, Sportand Culture, Japan, I have studied the optical reconstruction of sound from Pi sudski
wax cylinder records (1984-5), and the reconstruction and analysis of audiovisual resources of communities in the China Sea andJapan Sea (1985-6). I was also involved ina study organized by the National Ethnology Museum, Osaka, into northern cultures
around Japan based on Pi sudski northernmaterials (1984-6). I am still involved in the
study of cultural assets associated with visualand audio information, and I have followed
the development of new techniques for thispurpose. In this paper, I will describe some of
the new techniques that are available for the
research and reconstruction of cultural heritage containing visual and audio information.

2. Cultural heritage containing visual information
The scientific study of cultural heritage
containing visual information-such as paintings, sculptures, craftworks and buildings-

Department of Electronics and Information Engineering, Faculty of Engineering, Hokkai-Gakuen University (1-1 Minami 26 Nishi 11, Chuo-ku, Sapporo 064-0926)
E-mail: asakura@eli.hokkai-s-u.ac.jp

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JSAP International No.6 (July 2002)

Fig. 1: A bust imaged by X-ray tomography CT

has mainly involved two approaches. One is
the study of form, color and materials, suchas measuring the age of artifacts and inferring their place of origin by materials analysis.
The use of electromagnetic waves (e.g., X-ray
and light) is particularly useful in this respect
because it allows high-quality measurements
to be made in a non-contact and non-destructive manner. As a result, it has no effecton precious cultural heritage, and will probably be increasingly used for research in the
future. This section focuses primarily on theuse of optical methods for the study of visual
artifacts.

2.1 Optical research methods(1) Neutron beams
Neutron beams are used in autoradiography and neutron radiography to study theconstruction of craftworks and the pigmentsin paintings by examining the absorption andcapture of neutron beams. Autoradiography
uses nuclear reactors and accelerators to produce a beam of neutrons which is directed ata painting to produce an image by means ofradiation. It allows the elements contained in
the pigments to be studied based on temporal changes such as the half-life of radioactive
isotopes in the image.

(2) Gamma rays
Gamma rays are used in gamma radiography and gamma ray CT, in which the absorption of gamma rays is used to study the
structure and materials of sculptures, craftworks and the like.

(3) X rays
X-radiography and X-ray tomography
CT use the absorption of X rays to study the
structure, materials, pigments and the otherconstituents of paintings, sculptures, craftworks, buildings and so on. Another technique is emissiography, which makes use of
the electrons generated when a material issubjected to X-ray
irradiation, and is
widely used for the
study of pigmentsin paintings andcraftworks. X-ray
t o m o g r a p h y C T,
which involves theuse of image processing, is becoming a highly sophisticated technique.
Figure 1 shows
images obtained by
X-ray tomography CT of the outer surface(left side view) and inner surface (right sideview) of a herm restored in Rheinisches Landesmuseum Bonn in Germany, which was
found in a shipwreck near Mahdia, Tunisia.1)(4) Ultraviolet light
Ultraviolet light is used in UV reflectography and ultraviolet fluorescence analysis,
which uses the optical (visible-light) luminescence produced when an object is illuminated with ultraviolet light. Both of these techniques are used to study pigments and dyes
in paintings.

(6) Infrared light
These techniques, such as IR reflectography, IR transmittography and infrared photography, principally use the absorption andreflection of infrared light to investigate andstudy the underlying sketches in paintings.
Also, thermography, which uses the thermal
emission of infrared light, is used to study
the structure of buildings. An infrared reflectography system is an infrared image sensor
consisting of a monochromator for illumination, an infrared Vidicon, and a silicon CCD
camera, and is sensitive to a wide range ofinfrared wavelengths from 300 to 1800 nm.
Accordingly, infrared reflectography is able
to see through the surface grime and upper
paint layers that cover the underlying sketches in a painting, thereby revealing hidden information.
Figure 2 shows an infrared reflectography of “Christus am Kreuz” painted in
1503 by Lucas Cranach (1472-1553), a wellknown German artist of the Renaissance period. Here, a carefully composed underdrawing can be seen.2)(5) Visible light
Techniques that exploit theabsorption and reflection of visible light include stereo microscopy and laser microscopy, which
are used to investigate the shape,materials and production methodsof paintings and craftworks. Also,
polarizing microscopes (which use
polarized light) can be used to investigate the mineral nature of
sculptures and buildings. Recently,
techniques that involve the use ofinterference phenomena of the laser light, such as holography, holographic interference techniques,
electronic speckle interferencetechniques and moiré topography (which uses optical moiré patterns) have been used to analyze
the deformation of paintings andto analyze and record the threedimensional shape of sculpturesand craftworks. It is likely that laser
measurement methods using theproperties of laser light will be employed increasingly for the study ofcultural heritage containing visual
information.

Fig. 2: An infrared reflectography of “Christus am Kreus” by Lucas
CranachJSAP International No.6 (July 2002)13

top of the undercoat. The
paint consists of pigments
and a color development
agent, which is an organic adhesive that forms apaint when combined withpigments. Pigments canbe either inorganic or organic, and may consist ofvarious different materials
including natural pigments
and artificial pigments-therange of artificial pigments
has grown rapidly since
the late 18th century. Finally a layer of varnish is
applied. This covers thesurface of the painting
with a transparent film
which provides the paintwith a feeling of luster andtransparency, and prevents
discoloration and fading of
the paint.
This multi-layered
structure is kept in a finebalance. An old masterFig. 3: Interference pattern over a head statue obtained by the holographic interference methodthat has existed for many
years may suffer from all
2.2 Research and reconstruction ofkinds of problems, such as deterioration ofcultural heritage by optical methvarious materials, warping of the paint layerods
due to deformation or deterioration of theOver the last half-century, these opticalsupport, peeling of the undercoat and paintmethods have become common techniques
associated with reduced adhesion, and disfor the study of cultural heritage and have dicoloration or color fading due to exposure toversified along with the widespread progress
the atmosphere. Such paintings have often
in science and technology. In the future it isbeen restored numerous times and somelikely that many more methods will be develtimes look completely different from theoped. The importance of these methods, andoriginal painting, making it necessary to thorthe way in which they relate to the researchoughly investigate the original picture. Fromand restoration of cultural heritage, are disan art historian’s viewpoint, the study of thecussed below taking paintings as an example.
techniques and materials used in art is a subPaintings are generally built up in a seject of great interest. It is thus important toquence of layers consisting of a supporting
undertake an accurate comparative investigamaterial, a filler, an undercoat, paint, andtion of the original image and the image afvarnish. The supporting material (also called
ter reconstruction.
the base material) performs the role of supScientific research into the problems of
porting the undercoat and paint that makeimportant paintings is essential, and it is esup the painting. The filler forms a layer bepecially important to use a non-contact andtween the supporting material and the unnon-destructive approach. For this reason
dercoat, and its purpose is to adjust the suroptical methods are particularly promising.
face of the supporting material before the
Examples of such methods include the use
undercoat is applied. The undercoat smoothsof transmission X-ray photography to study
out the surface of the supporting material,
painting techniques and discover hidden picand improves the coloration and bondingtures (double layered paintings), the study ofproperties of the paint, which is applied on
pigments by emissiography, the identifica-

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JSAP International No.6 (July 2002)

tion of materials by ultraviolet fluorescence
detection, and the observation of underlying
sketches by infrared light as described above.
Although the research and reconstruction of cultural heritage are important starting points, the next important issue is theirpreservation. Furthermore, although it is ofcourse essential that important cultural assets
are kept for a long time, it is also important
to exhibit them as the heritage of all people.
From this viewpoint of preservation and exhibition, holographic techniques-wherebya three-dimensional image is obtained in acomplete form-are essential scientific methods for the recording and exhibition of cultural assets. Holography is a technique whichuses the diffraction and interference of lightto record all the information of an object as
an interference pattern, and for reproducing
it three-dimensionally in its complete form.
Accordingly, paintings, sculptures, craftworks
and the like can be recorded in holograms
and faithfully reproduced three-dimensionally. It is therefore a kind of replication technique, since the reproduced images are thesame as the real artifacts. By exhibiting holograms of cultural assets instead of the realthing, it becomes easier to exchange cultural
heritage over the whole world.3)
Research into the use of holographic
techniques to record and exhibit cultural assets was initially conducted at establishmentsin the former Soviet Union, such as the Institute of Physics, Ukrainian Academy of Sciences, but today precious cultural assets arerecorded in holograms and used in exhibitions in countries all over the world, including
Europe and the United States.
Holographic techniques are also being
used for the reconstruction and preservationof cultural assets such as paintings and sculptures in all European countries, especially Italy. Holographic interference techniques andelectronic speckle interference techniques
are used for this purpose. Specific examples
include the detection of internal defects inpaintings, such as warping of the paint layer
associated with deformation of a painting’s support and peeling of the undercoat andpaint, the detection of deformation associated with temperature changes as a preliminary step to the reconstruction of sculptures
and the like, and the precise measurement oferosion in artifacts.
A group at Universita degli Studi de L’
Aquila in Italy has developed a system that

automatically measures the shape of an object’s surface based on both sandwich holographic interference methods and electronic
speckle interference methods, and have obtained numerous interesting results in theirstudies of erosion and cracks, such as cracks
in paintings and sculptures.
Figure 3 shows an interference patternsuperimposed on a painted wooden headstatue with cracks5,6) (16th century, part of
the L’Aquila Museum collection) imaged by
the sandwich holographic interference method.4) There is a visible shift in the position of
the interference pattern on either side of acrack in the upper part, which indicates that
there is a difference in height between thetwo sides. The study of cultural heritage by
this sort of holographic interference method
is particularly commonplace in European museums.

3. Cultural heritage containing audio information

be broken. We therefore need scientific techniques for the research and reconstructionof audio artifacts, especially wax cylinder records. In this section I will introduce the research into the optical reproduction of soundfrom wax cylinder records, and I will also describe a few related issues.

3.1 Wax cylinder records7,8)
The records that were widely usedaround 1900 were of two types: cylinders
and disks. Cylinder recording began in 1877
with the invention of the tin foil phonographby Thomas Edison, and was improved by the
introduction of wax cylinders. On the other
hand, the disk format was devised by Emile
Berliner in 1887, and is the prototype ofmodern records. In addition to the different
shapes, these formats also differed in termsof the way in which sounds were recordedon cylinders, the vertical depth of the soundgrooves corresponds to the strength of thesound signal, whereas in a disk recording thesound signal is represented by the amountof horizontal displacement of the soundgrooves.
Cylinder records are made of tin foil,
wax or plastic, but wax was the most widelyused material. This material principally con-

Cultural heritage that contains audio
information-such as spoken language andfolk music-includes recording media such as
old-fashioned music-boxes, records and cassette tapes. Recently the appearance of digital media such as CDs has made it possible torecord and reproduce sounds withhigh fidelity. However, the records
of interest in terms of cultural
heritage include music boxes, wax
cylinder records, disk records, andmore recently tape records. Of
these, music boxes are craftworks
that are important items of cultural heritage but are mechanically complete and do not degrademechanically over long periods oftime, and have been preserved in
Fig 4: Wax cylinders and casesa nearly perfect condition. Accordingly, there are no problems withreproducing the recorded sound informasisted of stearic acid, which was mixed withtion, which is generally music. On the othersodium hydroxide, paraffin and aluminum
hand, wax cylinder records and disk records
oxide, resulting in a mixture closer to soap
remain in great numbers principally in Europe
than wax. A standard wax cylinder measuresand the United States, and contain precious
55 mm in diameter and is 105 mm long, andsound information such as spoken language
has grooves cut into it in a helical fashionand folk music, making them an importantwith a pitch of about 100 lines per inch. Thispart of the heritage of cultural anthropology.
is rotated at 160 rpm, and is thus capable
Due to the relationship between the materiof recording about 2 minutes of the sound.
als used in wax cylinders and disks and theThese recordings were produced in the era
environments in which they are placed, waxof acoustic recording, where the sound was
cylinders and disks are usually in an advanced
collected from a horn and the energy in thisstate of degradation and are often found tosound was used to cut the surface of the cyl-

inder with a stylus. The grooves in an ordinary cylinder have 50 µm maximum depth,
although in early recordings the maximum
depth may be as little as 10 µm. The frequency characteristics of sounds reproduced by
wax cylinder phonographs cover the soundrange of 500 Hz-3.5 kHz, which reflects thefrequency characteristics of the horn. Figure
4 shows some wax cylinders (on the left) andtheir cases (on the right), and shows how
wax cylinders are rather deteriorated.
One of the properties of wax cylinder
phonographs was that they allowed recordings to be made easily. Since the Edisontype phonographs could be used to makerecordings simply by changing the stylus, it
seems that they were often used not simply
as sound reproduction equipment but also as
a useful recording tool for people with an interest in music and sound, in much the same
way as tape recorders are used today. Historically, wax cylinders disappeared in a shorttime, but since they were manufactured intheir millions there must be many still in existence today. Most of them were used to record music, but some of the wax cylinders recorded by individuals are of great interest to
linguists and anthropologists, or as records ofthe speech of famous people of the time.
However, wax cylinder records
are generally stored in adverse
conditions, and many are found tohave surface defects arising fromdenaturing of the wax, scratches,
scrapes, and adhered foreign matter, and they are often found tobe cracked or broken. It is thus
often impossible to reproduce thesounds using the original phonographs. Considering this, as apreliminary stage to the reproducing operation the surface of thewax cylinder is cleaned and broken parts are restored, and replicas are also
made in order to preserve the wax cylinders
for the future. In the restoring process, it iswashed with degrading enzymes to remove
crystallized substances, and broken parts are
glued back on under a stereo microscope. A
replica is then produced by making a moldwith dentists’ silicon impression material, into
which the epoxy resin used in electron microscopy is poured.
After the restoring work has been completed, the sound can be reproduced. If thewax cylinder is in good condition it can be

JSAP International No.6 (July 2002)15

it is much better to use an optical reproduction method using the laser in a non-contact
manner after the restoring
work has been completed. Optical reproduction methods ofthe sound are discussed below.

3.2 Laser beam reflection method7,8,10,11)
The laser beam reflection
method is the basic opticalsound reproduction method,
Fig. 5: A stylus-type wax cylinder machine made by the National Museumof Anthropology in Canada
and the principle behind thismethod is illustrated in Fig. 6.
reproduced using the original phonograph.
As mentioned already, the sound grooves on
However, since acoustic recording and rethe surface of a wax cylinder are recorded as
production were the only techniques availsignals of varying depth. Therefore, if a wax
able in Edison’s time, a heavy stylus pressure
cylinder is illuminated with a narrowly-foof 20 g is required, and if the reproduction
cused beam of light as a probe, the reflected
is conducted using the original phonographlight will have an angular modulation caused
there is a danger that the surface might beby the inclination of the sound groove, andscratched by the stylus. Considering this, speit is thus possible to reproduce the sound by
cial reproduction equipment for wax cylindetecting this angle. The beam reflected atders is being developed in museum laboratothe surface is converted into a sound signal
ries to replace the original phonograph.
by a position detector located in the detectFigure 5 shows a stylus-type sound reing plane. The detecting signal is proportionproduction machine for wax cylinders which
al to the inclination of the sound groove, i.e.
was produced at the National Museum of
the differentiated sound signal, so it can be
Anthropology in Canada.9) Machines of thisintegrated to obtain the depth of the soundsort generally use either a sensor for thegroove, thereby converting it into the soundmeasurement of surface roughness or an ausignal. Figure 7 shows a laser beam reflecdio vibration sensor, and in either case thetion-type sound reproduction system.
stylus pressure is made extremely small to
As a result of investigating the reprosuppress the effect on the surface, and the
duced sound obtained with this method,sound grooves are measured with high sensiit was found that further study is required
tivity to reproduce the sound signal. Howevto study various problems, including noise,er, when a wax cylinder is in poor condition,echoes and tracking errors. The beam reflect-

ed from the surface of the wax cylinder is superimposed with speckle noise, which resultsin characteristic noise being added to the reproduced sound. This noise can be reduced
by adjusting the spot size of the illuminating
beam used as a probe, but it is impossible tocompletely eliminate the speckle noise. However, the noise can be reduced by an electricfilter since the characteristics of this noise are
known. The echo that appears in the reproduced sound arises due to the simultaneous
illumination of adjacent grooves by the illuminating beam. It is therefore essential toadjust the spot size of the illuminating beam
so as to track a single sound groove reliably. Furthermore in the optical reproduction
method, since we are not tracking the soundgrooves directly with a stylus as in the stylus
method, it is prone to tracking errors due toundulations in the sound groove on the wax
cylinder or position errors of the driving partin the reproduction system. When tracking
errors occur during reproduction of soundfrom the wax cylinder, the volume of the reproduced sound drops sharply and it is notpossible to reproduce the sound from theentire wax cylinder stably. This problem canbe solved by employing a scheme whereby a
two-dimensional position detecting device isused to detect tracking errors separately fromthe sound detection, and corrections are
made by feeding the tracking error signal tothe driving device (see Fig. 6).
In addition to the above problems, in order to eliminate stray light, a scheme is employed whereby an optical focusing system
is inserted into the light path of the reflectedbeam and a pinhole is positioned at the fo-

Detecting plane

R
ed
ct
fle
e
R

Lateral translation

Variation in theposition of the lightspot reflected fromthe sound groove

ht
lig

x
One-dimensional
position-sensitive device

WaxcylinderLens

Rotationz
Beam waist
positionFig. 6: Principle of the laser beam reflection method

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JSAP International No.6 (July 2002)

He-Ne laser

Fig. 7: A laser beam reflection- type sound reproduction system

Fig. 8: A negative cylinder

cal plane to eliminate stray light, after which
detection is performed. Also, to eliminate thenoise originating from the speckle phenomenon, the use of incoherent light from an infrared light-emitting diode instead of a laser
light source is also being tried out. However,this approach suffers from problems with adjustment of the optical path because the infrared light is invisible to the naked eye.

3.3 Reproduction of sound fromnegative cylinders8,12,13)
It has recently come to light that the National Museum of Anthropology in Berlin is
in possession of large numbers of wax cylinders with recordings of the folk music ofvarious countries in the world, as well as cylindrical metal “masters” that have been duplicated from them. These metallic cylinders(see Fig. 8) are called negatives or Galvanos(in the following they are referred to as negative recording cylinders or negative cylinders).
It used to be possible to produce duplicate
wax cylinders by using a negative cylinder as
a master, but this duplication technology has
now been lost. In any case, the production
process would involve melting the original
wax cylinders, which would be irretrievably
lost. Reproduction of sounds directly from anegative cylinder is not easy either. It is essentially impossible to reproduce sounds witha stylus because the sound information is recorded on banks (ridges) on the inner surfaceof the cylinder. However, optical methods
that use laser light do not need to make mechanical contact with the recorded parts, andit should therefore be possible to reproduce
sounds from negative cylinders in the same
way as wax cylinders.
Figure 9 shows a prototype sound reproduction machine for negative cylinders.
The reproduction machine consists of twoparts: a drive unit on the left and a control

unit on the right. Figure 10 shows
optical head is fixed to an XYZ-stage, wherea schematic diagram of the overby its position on the inside of the negative
all machine configuration. The
cylinder can be adjusted in three dimensions
drive unit comprises an opticalby the stage micrometers, allowing the optihead, which incorporates an optical head to be positioned at the optimal local system that detects the signal,
cation. At the optical head, the light focused
and a drive section that rotatesby a lens is directed at the recording surface
and moves the negative cylinder.
of the negative cylinder at an inclined angle,
Figure 11 shows a schematic diaand the reflected light is received by a posigram of the constructed opticaltion-sensitive device PSD. The output signal
head. The optical head is inserted
from the optical head is guided to a control
into the negative cylinder, which
unit, and is split into two signals correspondis attached to a cylindrical holder,ing to the two coordinates of the PSD planeand detects the signal recorded in the banks
in a signal converter. One of the two signalsof the protruding sound track. The negais the sound signal, and the other is a tracktive cylinder is fixed with screws to the inteing signal. The sound reproduction is fromrior of a large cylindrical holder. The cylindrithe sound signal, and the tracking signal iscal holder is able to rotate, and isdriven by a DC motor M1 via a belt
and pulleys. A circular disk withradial slits is attached to one endof the holder, and a pulse signal
whose frequency is proportional
to the rotation speed of the holder
is obtained by detecting the slits
with a transmitting type photosensor. The holder and DC motor
are attached to an X-stage mobile
platform which is driven by a pulse
motor M2. On the other hand, theFig. 9: A reproduction machine for negative cylinders

Drive unit�������
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������ �� ��������
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������

�������������

�����������������

������������

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Control unit
Fig. 10: Diagram of the reproduction machine

JSAP International No.6 (July 2002)

17

Negative cylinder

PSD

Fig. 11: Schematic diagram of the optical head

used for automatic tracking.
In general, sound reproduction fromnegative cylinders produces better soundquality than from ordinary wax cylinders. Thisis thought to be because the negative cylinders were produced straight after the soundrecording had been made on wax cylinders,
whereas the wax cylinders that exist today
have been played back many times in phonographs with a large stylus pressure.

3.4 Disk records8,14)
Although disk records are made of materials that in themselves are less prone todeterioration, they also crack more easily andare often broken (see Fig. 12). It is expectedthat optical methods will be useful for reproducing the sound from disk records of thissort. As mentioned above, the sound grooves
in a disk record vary within the plane of therecord, and the sound information is recorded as a horizontal variation of the soundgrooves. This makes it impossible to employ
the laser beam reflection method used forwax cylinder records. Therefore, another reproduction method has been developed that
exploits the diffraction phenomenon of thelaser light by the sound grooves.
When the sound groove of a disk record
is illuminated with a laser beam and the reflected light due to diffraction is observed, it
can be seen that the horizontal variation of
the sound groove affects the reflected light.
If the spot size of the laser beam is simi-

lar to the width of
the sound groove,then it is possible
to regard roughly
Laser lightthe sound groove
within the illuminated region as being a line. If thissort of line regionis illuminated witha coherent laser beam, the diffracted lightreflected from it will also have a linear structure together with the central specular spot.
Furthermore, the linear structure of this diffracted light is perpendicular to the directionof the straight line of the illuminated soundgroove. Accordingly, as Fig. 13 shows, it ispossible to detect the local direction of thesound groove by considering the direction of
the line pattern in the diffracted light. In thisway, it is possible to reproduce sound fromdisk records by a laser diffraction method.
However, this method is only applicable tomonaural recordings, and it is much moredifficult to track the sound groove with thelaser beam than in the case of wax cylinders.

point of sound quality. Since it is now possible to employ electronic amplification means,
it is conceivable that stylus-type sound reproduction with a very small stylus pressure may
prove to be an effective method. Research inthis direction has been performed using optical fibers.
One such method is implemented by
the system shown in Fig. 14. Laser light isfocused by a microscope objective lens andguided into one end of an optical fiber. The
optical fiber is fixed at a fulcrum close to
the other end, and a stylus which tracks thesound groove is attached near the end of thefiber. Since the stylus tracks the variationsin the depth of the sound groove, the lightemerging from the end of the optical fiberchanges direction according to the variations
in depth. An optical focusing system is used
to focus this onto the detection plane of aposition-sensitive device. Accordingly, theoutput of the position-sensitive device differs from that in the case of the laser beamreflection method, and an electrical signal is
obtained according to the variations in depthof the sound groove, which can be amplified
electronically to reproduce the sound.
Another method does away with the stylus and uses the optical fiber itself as a stylus to follow the sound groove as illustrated
in Fig. 15. Here, the core of the optical fiberis used as a mechanical guide for the soundgroove. Using an optical fiber with a core diameter of 150 µm, it is possible to track thesound groove using the edges of the sound

3.5 Use of optical fibers for soundreproduction15)
Since stylus-type sound reproduction
methods wear down the sound grooves, theimprovement of stylus methods has received
little consideration. However, since a stylus is
the best way of tracking the sound groove,it is the most suitable method from the view-

Central directionof disk record

OutputDiffraction
pattern
Position-sensitive
deviceIncidentbeam�(Incident beam
angle)

��

(Direction angle ofdiffraction pattern)
Mean sound groove
Sound groove

Central directionof disk record
Illuminating spot

�Fig. 12: Disk records

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JSAP International No.6 (July 2002)

Line tangent to sound groove

Fig. 13: Principle of the laser diffraction method

Line tangent tomean sound groove

Detecting
plane
Lens

Stylus
Laser

Optical fiber
Rotation

fulcrum

Objective
lens
Sound
grooveWax cylinder record
Fig. 14: Stylus-type sound reproduction method using an optical fiber with a stylus

groove as guides. In this case, the core is separated from the bottom of the sound groove,and the light emerging from the optical fiber
illuminates the bottom of the sound groove
under a slightly diffusing illumination condition. The light reflected from the soundgroove propagates toward the detecting
plane and is incident on the position-sensitive
device. Accordingly, this method solves the
problems of tracking errors and the size ofthe illuminating light spot that have occurredin the laser beam reflection method. However, since it involves the use of a laser lightsource, it still suffers from the problem ofspeckle noise as in the laser beam reflection
method. Furthermore, since the optical fiber
is made of quartz, which is much harder than
the wax cylinder material, it results in slightwear at the edges of the sound groove during reproduction. Since the sound is recordedat the bottom of the sound groove, this is of
no direct consequence, but from the viewpoint of non-destructive sound reproduction
there is much scope for improvement.

4. Conclusion: Multimedia databases
Visual and audio cultural heritage is
generally kept in museums and art galleries, which inevitably have to deal with large
volumes of visual and audio information. In
practice, they have to deal with masses ofphotographs, slides, moving pictures such asvideos, and audio recordings such as spoken
language and folk music. They may also needto maintain photographic records of every artifact from every angle, and may use image
processing for the automatic measurement
and retrieval of specimens by size, shape
and/or color. Databases can be compiled bydigitizing this information, and integrated
systems are now under development that willbring all of these activities together.
Although museums and art galleries area type of research laboratory, at the sametime they are generally required to put on

Fiber core

Detecting
plane

Laser
exhibitions. In thiscase, it becomes
Objective
Optical fiber
lens
necessary not only
Rotation
to exhibit suitablespecimens, but also
Wax cylinder recordt o p ro v i d e v i d e odisplays and spoFig. 15: Contacting sound reproduction method using an optical fiber without a stylus
ken commentaries,
and to find ways ofvisualizing things that cannot be seen. New
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Technology for their valuable cooperation in
the research for this report.

JSAP International No.6 (July 2002)

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