DIGITIZATION FOR PRESERVATION OF ANALOGUE
RECORDINGS
The research intends to focus on access to and long-term preservation
of analogue sound recordings. There are several compelling reasons for
which the digitization of analogue sound recordings must be initiated.
Although many analogue recordings have a long shelf life, they do degrade
upon playback. Some media, such as magnetic tape, are deteriorating rapidly.
Many rare and important recordings are being discarded, and the appropriate
playback equipment is becoming scarce. For example, there is only one
currently manufactured system that can play wax cylinders. Much research
is needed to ensure the proper digitization and preservation of these
very important cultural heritage materials.
Because of the sheer volume of analogue sound recordings in existence,
there is an urgent need to begin contemplating the proper method for digitization.
The British Library has catalogued over 2.5 million sound recordings (even
with a conservative estimate of digitization time at 30 minutes per recording,
the total digitization time required would be 1.25 million hours, 52,000
days, or 142 years). The Library of Congress has 2.5 million recordings
of various kinds that do not overlap significantly with those of the British
Library. Music libraries worldwide hold tens of thousands of recordings
(e.g., the music library at the University of Illinois at Urbana Champaign
holds 115,000 recordings). As of July 2003, OCLC WorldCat contained 1.7
million catalogue entries primarily for commercial sound recordings.
Two different methods will be considered for the digitization of phonograph
records: one mechanical and the other optical. In the traditional mechanical
means of sound reproduction using a stylus, one of the major challenges
consists in choosing the appropriate analogue-to-digital (A/D) conversion
system (turntable, tonearm, cartridge, preamp, interconnect cables, A/D
converter, etc.) to achieve archival-quality results. The wide range of
opinions on this subject, especially among the “golden ears,”
constitutes a major obstacle for many digitization projects. Most audio
digitization projects undertaken thus far have concentrated on access
rather than on preservation. If recordings are digitized for the purpose
of long-term preservation, extreme care must be taken so that the process
need not be repeated in the near future. The sound quality of various
combinations of components in the digitization process will be evaluated
through psychological experiments designed to determine, for example,
whether there are perceptual differences or preferences.
A radical alternative means of digitization is to optically scan the phonographs
for preservation and subsequently convert the scanned image to audio for
access. There are tremendous advantages to preserving phonograph recordings
as 2D or 3D images. This would make it possible to experiment freely with
methods of converting to audio—with a view to determining the best
method—without touching the recordings themselves.
Early this year, two physicists, Vitaliy Fadeyev and Carl Haber, from
Lawrence Berkeley National Laboratory
(LBNL) in California, in a ground-breaking experiment, successfully produced
high-quality sounds by optically scanning 78rpm records with video microscopes
and then converting the images to audio (Fadeyev and Haber 2003). Previously,
scientists used laser beams to track record grooves. This is the first
time that a 2D-scanned image was used to produce quality audio. The incredible
achievement was possible because of recent developments in high-resolution
video inspection systems used in medicine and metrology. These devices
possess sub-micron resolution, which is necessary for resolving the details
found in record grooves. This technology has tremendous potential for
audio preservation.
The initial LBNL experiment was performed on a few 78rpm recordings. Further
experiments will be conducted with the infrastructure to improve and extend
this technique for digitizing wax cylinders and stereo LPs. Since, in
most 78rpm records, the grooves are cut laterally, parallel to the surface
of the record, a 2D scan can be used to extract audio information. The
acquisition of the video microscope for the infrastructure will enable
the applicant to find a method for obtaining audio from 3D images, since
wax cylinders store information vertically, perpendicular to the record
surface, and stereo LPs use both lateral and vertical indentation to store
two channels of audio. Another important research goal using the microscope
to optically scan the discs is to reduce the amount of time required to
perform the scan. Fadeyev and Haber report that their scan took 50 minutes
for 1 second of audio (3000 times the real time). They do note, however,
that their scan was not optimized for time. Despite these challenges,
there are several significant advantages to this approach that warrant
further investigation. Optical scanning is possible even if the disc is
mechanically unplayable because it is too fragile, too valuable, or broken.
The effects of wear caused by stylus may be overcome by scanning the region
away from the inner surface of the groove where the stylus normally tracks.
Traditional sound restoration uses filters in the time or frequency domain.
With imaging, the quality of sound can be improved by removing artifacts
in the spatial domain where the noise originates. In general, imaging
captures more data than laser beams or mechanical stylus, thus allowing
more flexibility during the restoration process. The image files can be
stored as preservation copies and used as the basis for improved restoration
techniques in the future. The plan is to acquire a newer version of the
microscope that was used at LBNL, OGP Quest 450, which has improved resolution
and speed. It will be equipped with a rotation indexer for wax cylinder
scanning and with a DRS laser to facilitate the 3D scanning.
The result of the image-to-audio conversion will be quantitatively and
qualitatively compared with the best results obtained using mechanical
stylus. Furthermore, much effort will be invested in developing software
for audio restoration, which attempts to remove pops, clicks, and other
noise from older recordings. Other challenges include determining the
equalization curve used during the recording of 78 rpm discs, since it
was not until later that recording industry agreed on using the same equalization
curve, called RIAA, when producing the records. The speed of recording
was also not standardized thus the problem is correctly determining the
playback speed. It is hoped that these can be solved using digital signal
processing techniques.
This project will proceed in parallel with the digitization of McGill
music library’s 78rpm Jazz recording collection (funded by a three-year
FQRSC research grant) and digitization of a unique collection of Handel
LP recordings (funded by McGill’s Richard M. Tomlinson Digital Library
Innovation Awards). See MAPP. |
