Larson Davis System 824, Справочное руководство

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11-10 824 Reference Manual 11/2/00
sum calculation will include only the 3
rd
and/or 4
th
bins
but not the 1
st
or 2
nd
bin. In any case the noise energy sum
calculation will never include the first four bins.
• The fundamental must be higher than any of the first four
bins. There must not be excessive DC or near DC levels.
• THD+n must be at least 10 dB below the fundamental
level. There must be an identifiable tone.
• The fundamental frequency will be displayed whether
there is an identifiable tone or not.
• 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 mini-
mum 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
Pressing the Check
c
key while in the “THD” display puts
you in the check menu. The check menu is shown below:
The check menu offers the following options:
• View FFT - Takes you back to the FFT display
The bandwidth for each line is the
bandwidth setting divided by the
lines setting. • Bandwidth - Allows you to reduce the frequency band-
width from 20kHz to 200Hz. This setting provides the
following options:
200Hz, 500Hz, 1kHz, 2kHz, 5kHz, 10kHz, 20kHz