1.0 INTRODUCTION
The concept
of
the NAGRA-D was
to
build a truly professional format that
is
reliable, will last
for many years and lends itself well
to
archiving. The arguments regarding the format, choice
of
tape etc. are not covered here.
The NAGRA-D is a four channel--digital audio recorder having 24 bits-
per
sample recording
on 6.35mm metal oxide tape, on either 5" or 7" reels,
of
the tape type as used by the DASH
or PRODIGI formats.
It
accommodates the sampling frequencies
of
32 kHz, 44.1 kHz and 48
kHz rendering
it
suitable for all types
of
professional recording applications.
The
NAGRA-D
is
transparent
to
the AES bus giving connection possibilities to a wide range
of
external digital
equipment.
The sound
on
the NAGRA-D
is
recorded
on
helical track, by means
of
a rotary head (scanner)
containing 4 separate VHS heads
(2
for recording and 2 for playback), allowing read after
write (off tape monitoring) which can be heard through the two, level adjustable, headphone
outputs. The recorded tracks have a width of70 ttm and a pitch
of
80.7ttm. At the longitudinal
tape speed
of
99.25 mm/s, the scanner makes 62.5 revolutions
per
second (3750
r.p.m.)
for
a sampling frequency
of
48 kHz.
Three
longitudinal tracks (Control, Cue and Time code) are also recorded on the tape.
The
control track is used to synchronize the tape transport during playback. The
CUE
track can
record a mix
of
the four digital inputs, for search features,
or
alternatively it can record an
external cue microphone for commentary applications. This track can be monitored at high
speed,
in
either direction, allowing rapid sequence location audibly. (Please refer to the
instruction manual for the "footprint"
of
the format). The third longitudinal track is the
SMPTE/EBU time code track. The specifications
of
the format can be seen at the beginning
of
chapter
IV
"Time code"
The format
of
the NAGRA-D allows 4.608 x
10
6 bits per second to be recorded, meaning that
on
a 5" reel
of
tape 16.03 x
10
9 bits (16 giga bits). The combination
of
selected tape speed and
number
of
channels to
be
recorded gives tape durations to satisfy almost all applications.
Apart from the two AES digital inputs, four analog inputs are available for either line
or
microphone input sources. When
in
microphone operation each
of
the four inputs is switchable
between "T" powering, + 12V phantom and
+48V
phantom. The signal levels are adjusted
using the input potentiometers, and the levels are indicated on the four microprocessor
controlled meters. Microprocessor control
of
the entire machine gives almost limitless
possibilities, not only as far
as
the digital recording is concerned, but also for external control,
editing, fault diagnosis etc.
NOTE:
June 1994
The NAGRA-D has
no
user selections I switches inside all mode selections etc.
are made via
an
external PC
or
by the MENU mode.
I 1
