Professional Documents
Culture Documents
March 2006
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ISBN 1-932326-25-1
ISBN 978-1-932326-25-3
CLIR Publication No. 137
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iii
Contents
Foreword ........................................................................................................................iv
Preface .............................................................................................................................v
Introduction........................................................................................................... 1
The Preservation Challenge:
Changing Technologies for Recorded Sound ....................................... 1
Addressing the Challenge of Preserving Our Audio Heritage .......... 3
Foreword
For more than 115 years audio recordings have documented our culture and
enabled us to share artistic expressions and entertainment. Among all the me-
dia employed to record human creativity, sound recordings have undergone
particularly radical changes in the last 25 years. The “digital revolution” has
introduced new audio formats to consumers and library collections. Institu-
tional archives are now making a transition from preserving audio collections
on tape reels to creating digital files. Libraries and archives face both oppor-
tunities and challenges. New distribution systems have provided archives
with a broader universe from which to acquire collections, but, at the same
time, new formats have created new demands on our preservation resources.
In the National Recording Preservation Act of 2000, the U.S. Congress rec-
ognized the significance of sound recordings in our lives and the need to sus-
tain them for future generations. That law created in the Library of Congress
the National Recording Registry of historically, culturally, and aesthetically sig-
nificant recordings; the National Recording Preservation Foundation; and the
National Recording Preservation Board, a body of recording industry and li-
brary professionals who advise the Library of Congress on preservation issues.
Congress’s commitment to assuring the future of professional audio pres-
ervation was further demonstrated in the law’s directive to the Recording
Board to conduct a study of “the current state of sound recording archiving,
preservation and restoration activities.” The study was to include, according
to the legislation, an examination of “the establishment of clear standards for
copying old sound recordings.” This publication, the third in the series for the
preservation study and the first to address technical issues relating to audio
preservation, provides some useful indicators of progress in audio preservation
standards by reviewing current practices in copying analog discs and tapes.
While libraries develop ways to maintain and serve their digital collec-
tions, they still face challenges in maintaining audio collections in older for-
mats. Analog discs and tapes continue to require attention and pose particu-
lar challenges. For historical audio recordings to be accessible to researchers
in the future, specialized equipment must be maintained for playback. Many
of these analog recordings are deteriorating and must be reformatted while
they are still playable.
Authoritative manuals on how to create preservation copies of analog
audio recordings do not yet exist. There are, however, many highly skilled
preservation engineers working throughout the United States. To begin
to fulfill the Congressional mandate to establish standards for audio
preservation, the Library hosted a roundtable discussion in 2004 and
invited some of these talented engineers to share their methods for copying
recordings. The roundtable revealed agreement on most practices and on a
number of areas in which further research is needed. I am extremely grateful
to these professionals for donating their time and sharing their expertise.
As this report indicates, much more work remains if we are to preserve the
knowledge and expertise of these individuals in order to inform preservation
professionals in the future. The National Recording Preservation Board
is committed to documenting best practices for sustenance of our audio
heritage and sharing that work with the preservation community.
James H. Billington
Librarian of Congress
v
Preface
The ability to record and play back the sounds that surround us—human
voices, musical performances, the sounds of nature—has existed for little more
than 125 years. Yet the body of recorded sound that has been produced since
its inception in 1877 already constitutes one of the greatest creative, historical,
and scientific legacies of the United States. Given the importance of recorded
sound to our economic well-being, cultural enrichment, and ability to stay in-
formed by means of radio, television, and the World Wide Web, it is alarming
to realize that nearly all recorded sound is in peril of disappearing or becom-
ing inaccessible within a few generations.
Our audio heritage is fragile because it depends on technologies and me-
dia that are constantly improving and are thus constantly replaced and unsup-
ported by newer generations of hardware and software. Our continued ability
to hear recorded sound will depend, first and foremost, on technologies that
capture audio signal on obsolete formats—such as wire recordings, cylinders,
instantaneous lacquer discs—and migrate or reformat them onto current tech-
nologies. To ensure that the recorded sounds of the past century are available
for study and pleasure by future generations, we must not only preserve the
media on which they were recorded but also guarantee that we have the hard-
ware to play back the recordings, an understanding of the media, and the ex-
pertise to extract the best-possible sounds from antique recordings of all types.
That said, the formidable technical challenges are merely the proximate cause
of the fragility of these recordings. The ultimate challenge to providing access
now and in the future is political and organizational: As a society, we must
find the will and the resources to define this problem as a priority and to ad-
dress the problems that technology poses.
Recognizing the importance of our audio heritage to the nation, the U.S.
Congress created the National Recording Preservation Board (NRPB) in the
National Recording Preservation Act of 2000. Operating under the aegis of the
Library of Congress (LC), the NRPB is leading a national effort to address the
preservation of and access to the recorded sound held by libraries, archives,
historical societies, studio vaults, and private collectors as well as by others
who create, care for, and care about audio. In the legislation that created the
NRPB, Congress directed the Board and the Library to report on the current
state of recorded sound preservation and to develop a national plan to pre-
serve and broaden access to recorded sound. The Library asked the Council on
Library and Information Resources (CLIR) to commission background inves-
tigations and to convene experts to inform their study. This publication is the
third of a series that has been produced in response to the LC’s request. The
first two publications reported on the accessibility of out-of-print recordings
and copyright of recorded sound.*
This report is the first of two documents that will investigate procedures
to reformat sound on analog carriers to digital media or files. It summarizes
discussions and recommendations emerging from a meeting of leading audio
preservation engineers held January 29–30, 2004, to assess the present state of
standards and best practices for capturing sound from analog discs and tapes.
* Survey of Reissues of U. S. Recordings, by Tim Brooks (August 2005) and Copyright Issues
Relevant to Digital Preservation and Dissemination of Pre-1972 Commercial Sound Recordings by
Libraries and Archives, by June M. Besek (December 2005).
vi
PART ONE
Paul Kingsbury
INTRODUCTION
The Preservation Challenge:
Changing Technologies for Recorded Sound
The recording and playback of sound began with Thomas Edison’s
invention of the phonograph in 1877. In the wake of that landmark
innovation, history has seen the emergence of one innovative record-
ing technology after another. Each new technology has rapidly sup-
planted its predecessor. Thus, 10 years after the arrival of Edison’s
phonograph, Emile Berliner patented his disc gramophone. And
within a few decades, Edison’s cylinder recordings were largely
replaced by Berliner’s more-convenient flat audio discs, recorded
at approximately 78 revolutions per minute (rpm) and usually com-
posed of hard but brittle shellac. Following World War II, the shellac
78 gave way to the almost-simultaneous introduction of the flex-
ible vinyl 45-rpm single and 33-1/3–rpm long-playing (LP) record in
1948–1949 and to magnetic recording tape. Magnetic tape, developed
in Germany and brought to the United States after World War II,
came into widespread use in commercial recording sessions by the
late 1940s.
By the mid-1960s, when record companies began to offer for sale
prerecorded, continuous-loop, eight-track tapes, consumers began
participating in the audio tape revolution in earnest. Smaller, more-
convenient cassette tapes—both blank and prerecorded—reached
the market by the end of the 1960s. The next major breakthrough in
consumer playback came with the arrival of the first widely avail-
able digital carrier, the compact disc (CD), which was introduced in
1982. Since then, the parade of new playback and recording formats
has continued. As digital audio has gained precedence, new digital
carriers—digital versatile discs (DVDs) and MP3 players, among oth-
ers—are already jostling the CD for preeminence.
2 Capturing Analog Sound for Digital Preservation
1 Holland, Bill. 1997. Upgrading Labels’ Vaults No Easy Archival Task. Billboard
(July 19): 99.
Report of a Roundtable Discussion of Best Practices for Transferring Analog Discs and Tapes 3
digital. The following text summarizes these major points. For more
details, readers are invited to turn to part two, which contains the
original workflow documents along with extensive annotations
made by meeting participants.
Audio Tape
Audio tape is a German invention, perfected during World War II
when electrical giant AEG joined forces with the chemical firm I. G.
Farben to create recording tape covered with magnetized iron oxides.
Tape recording machines manufactured by the Brush and Ampex
companies made their way into some recording studios as early as
1947. The earliest audio tapes were paper based, followed not long
after by tapes with a cellulose acetate base, which were in wide use
from the 1940s into the early 1960s. Since that time, magnetic record-
ing tapes have been produced primarily on polyester tape (some-
times known by the trade name Mylar) in the United States; polyvi-
nyl chloride is also sometimes used in Europe.
Audio Tape
Choosing the playback speed. Once an original analog tape is in
condition to play, the correct playback speed must be determined.
The audio preservation engineer should have playback machines
capable of playing at all known speeds with all known tape head
configurations, plus a variable pitch control. When in doubt about a
tape’s speed, the engineer should start at 7-1/2 inches per second and
listen.
Expert listening is the first step in determining playback speed.
Roundtable members shared a few basic guidelines for determining
correct speed. For example, piano recordings are usually tuned to a
standard middle A (440 Hz). Music or language specialists may be
able to determine correct pitch on the basis of their knowledge of the
program content. In addition, the discussants recommended listen-
ing for low-level ambient, electrical-power-line hum (50 Hz for Euro-
pean recordings; 60 Hz for North American). Checking background
electrical hum with test equipment may help determine the correct
playback speed. Audio preservation engineers should be aware that
recording speed can vary throughout the recording; this is particu-
larly true of field recordings.
Preparing the tape for transfer. Roundtable members recom-
mended that engineers undertake the following steps when transfer-
ring sound from analog tape:
• Always adjust the azimuth of the tape head to the original source tape
being transferred to accommodate the possibility that the source
tape was originally recorded off azimuth. In addition to using an
oscilloscope to adjust for optimal high frequency and phase coher-
10 Capturing Analog Sound for Digital Preservation
Creating Metadata
Metadata is data about data. A digital recording can be accompa-
nied by several kinds of metadata, including descriptive (e.g., track
listings), administrative, and technical (e.g., a description of audio
hardware used in digital transfer, hardware settings, and data com-
pression used). Roundtable discussions of metadata were confined
almost exclusively to administrative and technical metadata, with
the understanding that metadata for preservation warrants a sepa-
rate and more detailed discussion.
The roundtable group strongly recommended that, whenever
possible, transfer engineers should note all documentation (e.g., box no-
tations) that accompanies the analog source tape. During the preservation
transfer process, transfer engineers should note anomalies in tape
(splice problems/repairs, speed variations, blocking/shedding, etc.)
as metadata to accompany the digital preservation copy. Such meta-
data could be embedded, eye legible, or both.
Slate announcements, i.e., brief, spoken, prefatory announce-
ments commonly used in identifying analog preservation copies,
need not be used in digital preservation copies if the engineer is already
embedding identifying metadata as part of the transfer process. Including
such announcements would be a needless redundancy.
Report of a Roundtable Discussion of Best Practices for Transferring Analog Discs and Tapes 13
Recommendations
In the final segment of the two-day roundtable meetings, partici-
pants made a series of broad recommendations for improving the
practice of analog audio transfer for preservation. The recommenda-
tions were grouped into categories. The salient and most widely sup-
ported recommendations appear below. Each paragraph includes the
recommendation’s priority, as voted by the roundtable participants.
The group was also asked to assign priority for action on these
recommendations. The sidebar on page 14 lists the 15 recommenda-
tions that members believed were most important, presented in order
of priority
Resources/Tools Needed
• Develop a one-page flowchart that offers a series of yes/no ques-
tions to help audio preservation archivists identify the composi-
tion of various types of audio discs and audio tapes. Such a chart
could be invaluable to staff of archives that outsource their audio
preservation transfers. Knowing the composition of the recording
at hand could significantly influence risk-assessment decisions for
the recordings to be transferred (Priority #7).
• Develop a reference chart of problematic media issues, including
tape brands, years of manufacture, etc. (Priority #8).
• Investigate the relevance of technology-transfer methods from
such fields as chemistry and materials science to audio preserva-
tion, particularly in identifying the composition of audio discs and
tapes and the nondestructive playback of discs (Priority #15).
Reference Materials
• Develop a Web site that identifies the core competencies for
audio preservation engineers. This information could be distrib-
uted in video format (Priority #1; see related item below, Core
Competencies).
• Develop a Web-based clearinghouse for information on how
archives can develop a program of digital preservation transfer,
including, for example, information on potential sources of grants
for audio preservation; a resource list of experts on audio preser-
vation and transfer; lists of equipment for audio preservation and
14 Capturing Analog Sound for Digital Preservation
Standards
• Develop guidelines for archives on how to judge when to use
automated transfer of analog audio to digital preservation copies.
This is a complex risk-assessment task. Those doing automated
transfers need guidelines and sources of expertise (Priority #4).
• Develop a collation of the existing relevant audio engineering
standards from organizations such as AES, ARSC, IASA, and
NARAS. Roundtable members recommended reviewing all inter-
national standards (Priority #9).
Conclusion
As new audio technologies evolve and supplant older ones, we
risk losing decades of spoken-word and musical recordings that
are valuable not only as commercial products but also as cultural
touchstones that document who we are, what we feel, and how we
experience our world. At present, there are both audio engineers and
equipment capable of transferring even the oldest analog recordings
safely to digital. But this will not be true for long. As one roundtable
participant noted, “The pool of expertise is shrinking every day.” If
key technical knowledge is not passed along soon, thousands of re-
cordings may not be accessible to America’s listeners 20 or 30 years
from now.
Roundtable members agreed that sharing their expertise with
colleagues in audio archiving and audio engineering, both now and
in the future, is of vital importance. Participants noted that some
of the leading associations in the audio field—such as AES, ARSC,
IASA, and NARAS—have unilateral efforts afoot that may lead to
some progress in developing standards for digital preservation. They
agreed that more communication across these groups—through the
Web and group meetings—should be encouraged to facilitate the
sharing of information and recommendations.
17
PART TWO
1. Pretransfer issues
1.1. Inspecting, preparing, and cleaning the
source materials
1.1.1. Determining the composition (polyester [e.g., Mylar],
acetate, paper) and the thickness
Optimal practice: Inspect the tape visually; this is usually adequate.
Consider nondestructive testing methods. Tape boxes and labels can
aid identification but are not always reliable. The optimal inspection
technique is nonintrusive; however, the use of destructive techniques
can sometimes be justified.
Occasionally, a single tape reel held in an archive or a collec-
tion may hold tapes of differing compositions. These tapes may be
spliced or simply wound together. Such reels ought to be set aside
and examined individually.
Thickness is important because it can help determine how a tape
responds to stress and how it should be handled. In addition, tape
thickness is an indication of tape length, which may be helpful in
predicting program length.
Recommendation: Produce a flowchart or logic tool to identify
the composition of the tape.
1.1.2.1. Brittleness
Brittleness affects acetate and paper tape.
Optimal practice: Visually inspect the tape, then slowly wind
and play it. If a scrap piece is available, test it by bending. Identify
brittleness to implement appropriate handling techniques.
1.1.2.3.1. Cupping
Cupping is a deformation in which the tape, when viewed end-on,
appears curled instead of flat. Cupping is most common in acetate
tape that has been stored in damp conditions.
Optimal practice: Let the tape sit as a B-wind for three to six
months if possible. If that amount of time is not available, the tape
may still benefit from a shorter period in the B-wind configuration.
If a dub must be made immediately, either (1) adjust the tension of
the playback machine or (2) use pressure pads. A tape that is severely
cupped could expand and come off the reel. For this reason, it is im-
portant to wind slowly and to monitor the take-up wind.
A B-wind involves packing the tape with the oxide on the out-
side and the backing on the inside. (Other wind descriptions that
preservationists should be aware of are A-wind, flat wind, library
wind, fast wind, tail-in wind, and tail-out wind.)
1.1.2.3.3. Leader
There are two types of leader: plastic and paper. Plastic leaders can
accumulate electrostatic charges that, if discharged during playback,
could disrupt the signal.
Lack of consensus: Sprays are available to help remove elec-
trostatic charges. Participants disagreed on whether such spraying
could contaminate the tape. One engineer noted that to his knowl-
edge, use of such sprays was not an accepted practice. He further
stated that he was unaware of any research confirming their effects.
Thus, the value of sprays cannot be supported or refuted at this
point.
Optimal practice: When repairing splices as part of routine con-
servation activity, replace plastic leaders with paper leaders. Proper
control of room humidity can also reduce electrostatic buildup.
2 For more information on problems faced when playing back open reel
tapes, see D. Michael Shields, Dennis D. Rooney, and Seth B. Winner. 2003.
Considerations in the Playback of Archival Analog Magnetic Recordings with
Wide Recorded Tracks. ARSC Journal, 34(1): 48–53.
20 Capturing Analog Sound for Digital Preservation
1.1.3.2. Mold
Optimal practice: Vacuum with a HEPA filter. Follow with Pellon
cleaning on both sides of tape—backing and oxide.
Note: This procedure is a potential health hazard, and appropri-
ate protection is advised. Cleaning should be done in an environ-
ment where it will not place other media at risk for contamination.
1.1.3.3. Stickiness
Two distinct conditions may cause tapes to become sticky and emit
a telltale squealing noise during playback. One condition is sticky
shed, also known as binder breakdown. It affects polyester tape and is
an indication of binder hydrolysis. The second is lubricant loss, which
primarily affects acetate tapes.
The most common practice for making sticky polyester tapes
playable is extended baking at low heat in a scientific or convection
oven. Other treatment methods include using environmental cham-
bers and desiccants. Alternative methods should be explored.
Report of a Roundtable Discussion of Best Practices for Transferring Analog Discs and Tapes 21
2. Transfer
2.1. Guidelines or methods for setting playback curves
Most tapes conform to standard playback curves, either NAB or
CCIR. The CCIR curve is typical in Europe, and the NAB curve is
used in the Americas. The playback-machine curve should match the
source.
To determine the proper playback curve, the engineer should
take note of documentation included on the tape or with the tape box
and use EQ-alignment reference tones provided at the beginning of
the tape.
If there are no EQ reference tones on the tape, the engineer
should mount a standard alignment tape conforming to the pre-
sumed general EQ curve and align the playback deck’s EQ to that
tape. The source tape should then be mounted, and the azimuth
should be adjusted to match that tape. Determining the proper play-
back curve of a tape with no documentation or tones can be difficult.
If the EQ tones are included on the source tape, the playback
equalization should be set to play back the tones as nearly as possi-
ble to the same level. If there is a large discrepancy in this result, the
operator should suspect that the overall EQ curve is different from
that in the player. Switching to another type of EQ curve may allow
the tones to be adjusted to the same level.
they wondered whether “overs” are ever acceptable. One view holds
that they are not. Some believe that decisions concerning whether it
is easier to remove these with software filtering or to raise low-level
signals must be made in conjunction with the rest of the music and
available processing capabilities.
4. Pretransfer issues
4.1. Inspecting, preparing, and cleaning the
source materials
4.1.1. Determining the composition (shellac, lacquer/
acetate, aluminum, vinyl, metal parts)
Identify disc composition before cleaning or outsourcing for transfer
in order to specify cleaning methods and to anticipate problems. Ex-
perienced engineers can readily identify disc composition.
Recommendation: Research on the various formulations of shel-
lac discs is needed. Advanced materials science could be helpful in
this area.
4.1.2.5. Warps
Some warped discs can be played at a much lower speed than origi-
nally intended; in other cases, additional tracking force can be ap-
plied. The deciding factor is the severity of the warping. Take note
of speed for metadata and note if any EQ is applied. Do not apply
playback EQ curves during low-speed transfers.
A vacuum turntable works with vinyl but not shellac. It is also
an expensive, highly specialized piece of equipment.
5. Transfer
5.1. Methods or techniques for setting
playback EQ curves
If the type of recording EQ curve for a disc recording is not known
or cannot be assumed with a high degree of assurance, or if no re-
cording EQ was used (as with the early acoustic recordings), it is
generally recommended that the disc be transferred “flat” with no
playback EQ curve compensation. If necessary, these recordings
can be adjusted post-transfer. The EQ used should be noted in the
documentation. Not all phono preamplifiers allow for the EQ to be
switched off, and switching off the EQ is not easy to do with most
phono preamps. The Recording Industry Association of America
(RIAA) playback curve is often designed into the constant-velocity
to constant-amplitude compensation that is intended to be used with
magnetic (dynamic) phono cartridges. If one uses a flat amplifier in-
stead of the RIAA magnetic preamp circuit, the result is a very tinny
sound from a magnetic cartridge. Although this can be useful for
preservation, it is not recommended for standard playback. A sepa-
rate preamp velocity-compensation equalizer is required to convert
the magnetic cartridge response to constant amplitude that does not
have RIAA compensation added as well. This circuit is rarely found
in any commercial preamps.
7. Other Issues
7.1. Choosing sampling rate and bit depth
Recommendation from George Massenburg: 96 kHz, 24 bit, linear
PCM files are the minimum standard for digital audio preservation
files.
Reasoning: The emerging standard is the DVD, on which audio
is 96 kHz. Storage space is becoming cheaper all the time. IASA has
embraced 96 kHz as its specification, and we want to be interoper-
able with Europe. At least one roundtable member recommended
sampling at 88.2kHz in order to best produce a 44.1kHz file. It was
pointed out that good digital converters can now down sample 96
kHz to 44.1 kHz much better than they used to, with negligible loss
of audio fidelity. And the point was made that 44.1 kHz would be
used only for access copies, not for preservation copies. A minuscule
loss of audio quality in such copies would be acceptable to most at-
tending the roundtable.
Although there was some discussion that preservation of lower-
fidelity media (e.g., oral histories on cassette) might not currently
benefit from 96kHz/24 bit, 96kHz/24 bit is nevertheless recom-
mended for all media and all content whenever possible. One cannot
foresee how the transferred audio may eventually be repurposed
and how future restoration technologies might be used.
One engineer noted that as of early 2004, the AES had a proposal
on the table recommending setting a new digital preservation stan-
dard at 192 kHz/24 bits.
7.2. Compromises
To accommodate limited budgets or other resources, preservation
reformatting often involves compromises between best practices and
acceptable results. Roundtable participants suggested that guidelines
be created to assist in making decisions that result in compromises to
the quality of the product.
• Define and spell out compromises and trade-offs.
• Provide guidance to all institutions, regardless of size and budget,
on how to deal with any needed compromises between best prac-
tices and acceptable results.
Report of a Roundtable Discussion of Best Practices for Transferring Analog Discs and Tapes 33
APPENDIX 1
George Massenburg
1.1.3 Linearity
1.1.6 Noise
• level (weighting)
Recommend: 110dBFS A-weighted or better
• quality and nature of artifacts
Refer to FFT evaluation of performance, observe relatively few spikes
2. Processing
2.1 Baseline procedures
APPENDIX 2
Meeting Participants
Bill Klinger
Association for Recorded
Sound Collections