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lidate any previous free-field warble tone calibration, and this must
be repeated when warble tone testing is required.
4.1.2. Level Setting
The calibration tone from the speech recording should be played
and the external amplifier volume control used to give a reading
of 90dBSPL for a 70dBHL instrument setting. Once set, no further
adjustment should be made to the external amplifier or graphic
equalizer controls (if used for equalisation).
If more than one set of test recordings is to be used then the
following procedure can be used to allow for minor differences
in calibration levels:
• Set up as above for the most commonly used test recording.
• Measure the actual listening point level for when playing the
calibration tone of each alternative set of test recordings.
• For each alternative set of test recordings produce a correction
table (the difference between the actual listening point level
measured and 90dBSPL).
• Apply this correction to the output level of the audiometer while
conducting a test to compensate for the minor difference in
calibration level.
4.2. Calibrating the Competing Noise Channel
Refer directly to Section 5.2 of this appendix if a warble tone cali-
bration is not to be carried out. If warble tones are to be calibrated
(or if the warble tone calibration method is used to equalise the
speech frequency response) then the competing noise channel may
be calibrated after the warble procedure as the instrument will
already be in the appropriate display mode for this operation.