Here's my letter from Justin Shirley-Smith:
In answer to your questions.
The earliest digital tape in the Queen audio archive is dated 20th
September 1983. This is an F1 format cassette-tape of rough mixes from
The Works sessions which is stereo only.
The earliest digital multi-track tape in the Queen audio archive is
dated 18th September 1987. This is a DASH format tape which has 24
tracks. This tape contains transfers of various Brian songs from analog
tapes done at the time Brian first bought the machines - just prior to
The Miracle sessions.
Obviously, any type of tape damage (water, fire, heat, breakage etc)
could result in loss of information if serious enough, but he most
important thing to avoid is proximity to anything magnetic, such as a
loud speaker. A magnetic field will erase information from analog or
digital tapes because they are both magnetic media. This is the first
thing you learn in a recording studio for obvious reasons. Since
computer hard disks (+ floppy discs, jazz and zip etc) are also
magnetic media, they too are best kept away from magnetic fields.
In the beginning of automated mixing, the fader move data was recorded
on one track per pass alternately, using up two tracks of the
multi-track tape. In the Queen Audio archive this only happened on
Musicland tapes. Starting from The Works (recorded at The Record Plant
LA), one track of the multi-track tape was used to record time-code.
This technology comes from the movie industry and is used for
synchronising things together, such as music to picture and, in the
audio world, facilitated the first 48 track playback by synch'ing one
24 track tape to another 24 track tape. From memory, I think the first
48 track Queen songs are Hard Life and Hammer To Fall. The time code
was also used to allow a mix computer to recognise which part of the
tape was playing, and therefore which fader moves to perform. The fader
mix data was stored separately on computer disks of various kinds.
Automated mixing still works in the same way, by chasing time-code.