9/29/09 AUD (Optional) 13-21
• If a harmonic is less than 10 dB above the noise floor, the
level of the harmonic is marked with an asterisk. The
noise floor is calculated as the maximum of the
minimum in the two adjacent valleys.
• If one of the harmonic’s side-bands is higher than the
harmonic then the harmonic is marked with an asterisk.
THD Check Menu Press the check key c to open the THD check menu. This
menu contains the following items.
• View FFT -View the current FFT spectrum.
• 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.
• Bandwidth -Setting to select the FFT bandwidth,
choices are include 200, 500, 1k, 2k, 5k, 10k and 20k
Hertz. The default is 10kHz. If the THD of signals with
fundamental frequencies above 2500Hz is to be measure,
choose a Bandwidth of 20kHz so that the 2nd through
4th harmonics are captured.
Pulse/FM Display
The Pulse/FM displays provide measurements to qualify the
pulsed amplitude and frequency modulation (FM) response
of an audiometer.
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