If necessary, adjustments should be made using the amplifier controls or
an additional graphic equalizer to achieve this response.
As an alternative to using an external speech source, the warble-tone
calibration method and controls (see Section A2.5) may be used to
achieve this response. Note that this will invalidate any previous free-field
warble tone calibration, and this must be repeated when warble tone
testing is required.
A2.4.1.2 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
A2.4.2 Calibrating the Competing Noise Channel
Refer directly to Section A2.5.2 if a warble tone calibration 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.
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