E Alignment Procedures
The electrlcal tests and allgnments of a tape
recorder
consist
basicly
ln achleving an overall fre-
quency
response
withln
tolerances and the best compromlse between the
amount
of
pre-emphasis
and
effective signal-to-noise ratio. For the best compromise it is necessary
to use a
pre-emphasis
ln
recording
and an
equal but opposite de-emphasis ln
reproductlon
in order to achleve a
flat
overall
response.
It ls therefore, in
no
way sufflcient to achleve a
flat
overall
response which
could stlll
lead to wide
dlscrepancies in
frequency response it
-
as is very
common
-
the tape
is
not
played
back
on
the
machine
that it
was recorded on.
The
frequency response of the
playback
channel has been
specified by internatlonal standards,
The
frequency response
of the
record
channel, however, ls
not
standardised. It should be
ananged
ln such a
way
as
to
give
a
flat overall response with the type of tape in use.
The
most usual stardards
for
the
frequency
response of the
playback
channel
are
the
CCIR
recom-
mendations No,135
(London
1953)
and No.209
(Warsaw)
whichhavebeenadoptedbymany
natlonal
standard
committees.
Apart
from the
CCIR specifications there is
the
NAB standard which
is widely used in the U.S.A. The STUDER
l-37
normally
uses the CCIR characteristics but it can
be supplied
with NAB equalisatlon upon request.
In
special
cases where the
amplltude
dlstrlbutlon in the
various
audio
frequency ranges
ls dlffer-
ent
from that normally encountered, it might be
desirable
to employ
an
equallsatlon
characterlstlc
which dlffers
from
the usual standards.
The testing or
alignment
of the
recorder
must al.ways begln wlth the
settlng
up of the
playback
channel accordlng
to the
standard 1n use. Subsequently,
the record
channel should be adjusted so
as
to obtain
a
flat
overall response with the
particular
brand of tape in use.
The
playback
channel is normally tested
and
allgned by
means of
test tapes. In order to make them
slmple to use,the necessary technlcal lnformatlon such as
frequency, level etc.
is
glven
by
re-
corded
announcements.
The duration of the various recordlngs Is usually made to correspond to
the tlme
normally
taken
for the varlous
adjustments.
To maintain thelr value
as secondary stand-
ards
these
test
tapes should be handled
and
stored wlth
great
care.
The most important
part
of the test or reference tape is the azlmuth allgnment bard. A
good
high
frequency
response
ls only
posslble
when the
gaps
of the
record
and
replay
heads are
exactly
parallel
to each other. But
as
tapes
are
more often than not
played
back on a dlfferent machlne to
the one they were
recorded
on, lt ls
necessary for
purposes
of
programme
interchange,
for the
gaps
of
all
the heads on
all
machines to be
set at
the same
angle.
The international standard
speclflcation ls that:
THE GAP SHOULD BE AT
RIGHT
ANGLES TO
THE D]RECTION OF TAPE TRAVEL.
Exept for the lnstructlons
for
head allgnment ard the
measurements
of the
mechanical
propertles
under
E .3,
all
the following test and calllbratlon instructlons
refer
to one channel. They should,
of course, be
repeated for
all channels.
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