Mark Pomeroy wrote:
> The Royal Academy archives contains a number of audio recordings. These are
> all on standard compact cassettes, a format I have never been entirely
> comfortable with; indeed many are showing their age. This year it should be
> possible to copy these recordings on to a medium of my choice.
You are right to be concerned about them as a long-term preservation medium.
They are likely to have problems with binding (where the magnetic material
becomes detached from the film which forms the tape) and print-through,
where signals from one part of the tape become imprinted through to tape
adjacent in the spool. This latter effect is audible as faint echoes with a delay
equivalent to the time it takes the spool in the cassette to make one revolution.
It won't happen if the tapes are regularly respooled.
The audio signal itself can also be prone to decay to a greater or lesser
extent depending on the quality of the original magnetic carrier and the
intensity of the signals in the recorder used to make the tape.
>
> The primary purpose is to ensure ongoing preservation. However, the
> Academy's collections are to be increasingly accessible on-line. I am very
> keen that my audio holdings should be in a format that facilitates their
> inclusion in an on-line resource.
>
> DAT, CD-ROM, WORM, DVD, MINI-DVD, hard disk? What? How?
Preservation and accessibility are two separate problems and you should
deal with them separately. You will be creating electronic records once
you do this and you should treat them as such, at least as far as
preservation and access goes. The separation makes your life easier,
not more difficult.
For preservation, you are concerned about two things:
(1) The data format
(2) The physical carrier
You want (1) to be standard and well-defined so that you are not dependent
on one manufacturer for dealing with the information in future. You also
want to ensure that the data format offers quality no worse than that
which the original recording medium offered. You want (2) to be something
with a predictable lifetime that offers best value in terms of overall
management overhead (trading off cheap media which need frequent replacement
against expensive ones which need replacing less frequently, for instance.)
You may also need to consider the quality of the digitisation process.
This comparable to deciding what resolution you are going to scan an image
at; audio has two basic parameters, the sample size and the sampling frequency.
22Khz sampling frequency with 16-bit samples is more than adequate for
cassette tapes. For certain types of recording (e.g. speech) you can afford
to use lower sample sizes and/or sampling frequencies, but it does depend on
what the speech was recorded for.
DAT is a great recording medium but doesn't have predictable long-term
storage properties. It is best avoided for preservation purposes. WORM optical
is a niche market and expensive. Unless you already have facilities for dealing
with it I can't see why you would want to use it, although it doesn't
have any specific preservation problems. CD-R would be OK, but you need to
choose between making CD audio disks (in which case sampling, etc. is
fixed, as it also is with DAT) or CD data disks containing encoded digital audio files.
Recordable DVD is not yet a stable technology, so I would be wary of it.
I haven't heard of mini-dvd. Hard disks will just need backing up on something
else, although they make manipulating your collection very straightforward.
Avoid any compression technique such as MP3 or those used on mini-disks (perhaps
that's what you meant by mini-dvd ?) They are fine for delivery but not
for archival copies.
For delivery via an online resource, you may be using streaming real
audio, MP3, WAV files with a variety of audio codecs, or whatever happens to be
popular and available to the public at the time. These things change rapidly
and it's always very easy to convert your archival copies to whatever is needed
for delivery, often on-the-fly. (cf storing scanned images as TIFF files but
serving them up on a web site as JPEG files.)
Hope this helps
Kevin Ashley
Digital Preservation
ULCC
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