Jade 1.0 Technical Note
Using a Single Level Calibrator
If you only have a single level calibrator, it is sometimes possible
to perform a "pseudo" dual level calibration. This is
only possible if the sound level meter produces a DC voltage that
depends on the displayed dB value rather than on the actual dB
Note: Although a pseudo-dual level calibration will probably produce
better results than a single level calibration, it is not as accurate
as a true dual level calibration. You are strongly recommended
to use true dual level calibrations.
Performing a Pseudo-Dual Calibration
To use pseudo-dual level calibrations, do the following:
- Attach the calibrator to the meter. Set the meter to an appropriate
range and turn on both the calibrator and the meter. You do not
need to connect the meter to the computer.
- Using the calibration adjustment on the meter, alter the adjustment
control until the meter displays a dB value at least 1 dB below
the nominal calibration value. If the calibration adjustment does
not have sufficient range to achieve this, you will not be able
to do a pseudo-dual level calibration. Ideally, you should find
a value at least 2 or 3 dB below the nominal calibration value.
Make a note of this lower value. This will be the first calibration
level for your pseudo-dual level calibration.
- As a result of step 2, the meter is now uncalibrated. You
should therefore use the calibration adjustment to readjust the
meter so that it displays the nominal value of the calibrator.
- Create a dual level calibrator in the calibrator library.
The first level is the level obtained in step 2. The second level
is the nominal value of the calibrator.
Tip: It is a good idea to use the Note text box to record
the fact that this calibrator is a single level calibrator used
as pseudo-dual level calibrator.
You can now use the pseudo-dual level calibrator to calibrate
the meter as normal:
- For the first calibration level, you use the calibrator on
its only level (ignore the message telling you to set it to the
pseudo first level) but you do adjust the meter to display this
pseudo first level. This means that from an acoustical point of
view the meter is now incorrectly calibrated. However, provided
the meter outputs a voltage dependent solely on the displayed
value, Jade Capture registers a valid first calibration level
voltage from the DC output.
- For the second calibration level, you again use the calibrator
on its only level (this time matching the message). You must also
adjust the meter to display this true level, ensuring a correct
acoustical calibration for any subsequent data capture.
To summarize, you can only use pseudo-dual level calibration if
the following conditions are met:
- The voltage on the meter's DC output reflects the displayed
value rather than the actual sound level.
- The meter can be adjusted using the calibration adjustment
to read a value at least 1 dB and preferably at least 2 or 3 dB
below the nominal calibration value.
- When you edit a meter in the meter library, editing any details
(except the meter's name and note) invalidates the last calibration
for the meter. You must therefore calibrate the meter before using
it again for data capture.
Copyright © Ptolemy Services 1997
Most recent revision 8 September 1997