9/29/09 AUD (Optional) 13-17
+30dB, the gain will be changed to 0dB whenever the
instrument becomes overloaded or the level is within 8dB of
the overload level for 1.5 seconds. The instrument will beep
once when the gain is changed automatically to 0dB and
twice when it is automatically changed to +30dB.
Linearity FFT Check Menu Press the check key c to open the Linearity FFT check
menu, shown below.
The Linearity FFT check menu contains the following items:
• Set Reference -Set the reference level to the current
level, i.e. zero the display.
• Reference Lvl -Reference level setting that may be
entered manually.
• Gain -Changes the gain setting of the instrument.
Generally use 0dB gain for levels at 70dB SPL and
above, and 30dB gain for levels less than 70dB SPL. The
Auto Gain Control (AGC) function of the linearity
displays step between 0 and 30 dB gain, if the gain
setting is something other than 0 or 30 the AGC function
is inhibited.
• Weighting -This setting selects either A, C or Flat
frequency weighting as a filter prior to FFT filtering.
• Trigger Level -The Trigger Level setting defines the
level below which the automatic frequency lock becomes
active.
Note: The Linearity FFT display when using A or C
weighting should not be used to measure frequency response
and is not good to use for absolute amplitude measurement.
Always zero the display at your reference point and use the
relative level to see changes in amplitude relative to that
reference. Note also that the FFT's A and C weighting filters
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