Casella CEL CEL-414 - Manual (Page 36)

4. Connect the sound level meter (and
filter) with the tape recorder
following Figures 14, 15 or 16 (as
relevant) for recording.
5. Set the sound level meter controls as
follows:
P-I-F-S F (Fast),
A-L-FA-FL or
A-C-FA-FL L (Linear), A, or C if no
filter is used,
FL (Linear plus filter) or
FA (A-weighted plus
filter) if a filter is used,
and set the filter to
1 kHz,
80-50-20 80 (High range)
(Hi-Med-Lo on
CEL-493/3 to Med).
6. If an external CEL filter set is used,
set its controls as follows:
RANGE High,
WEIGHTING Octave or 1 ⁄ 3 Oct as
required.
7. If not switched on, switch all the
equipment ON, and give it sufficient
time to stabilize at the specified
accuracy.
When used with sound level meters
at standard temperature and
pressure, CEL-284/2 and CEL-282
Calibrators generate a sound level of
114 dB at 1 kHz.
8. Use the FUNCTION buttons on the
sound level meter, select SPL
measurement mode.
9. Use the push buttons on any external
filter set to select either All Pass, or
the 1 kHz band.
10. Set the tape recorder to record mode.
11. For accurately repeatable recordings,
adjust the tape recorder record level
control until the 114 dB signal from
the calibrator gives a reading of
-6 dB on the tape recorder VU
meter. (On some recorders, it may
be necessary to estimate this
reading).
This setting gives tape saturation at
120 dB, so that if the recorder has a
dynamic recording range of 60 dB, in
theory it will be able to record
signals ranging in level from 60 to
120 dB. However, in practice the
lowest recording level will be limited
by the 80 dB minimum scale reading
set on the sound level meter.
12. When the signals to be recorded fall
within the 80 to 120 dB range,
proceed directly to step 15.
13. If the actual recording levels are found
to be, or anticipated to be higher
than 120 dB, adjust the RECORD
LEVEL so that the 114 dB calibration
signal gives a more negative reading
on the VU meter.
When the VU reading is estimated
(which it usually must be at these
levels) repeatability from one series
of recordings to another may suffer.
Therefore, either keep the RECORD
LEVEL control in the same position
for ALL recordings, or perform a
new calibration for EACH series of
measurements.
The dynamic range of the recorder is
limited, so that the higher that the
required maximum level to be
recorded becomes, the higher the
tape noise floor will also become.
Page 32 - General CEL Sound Level Meters Handbook