Larson Davis 824 User Manual

12-10 824 Reference Manual 9/29/09
• The window must be in Hanning mode after an overall
reset. If not, “Available only in Hanning Window” is
shown.
• The fundamental must be above the 4
th
bin or 10 Hz
whichever is higher. In the case where the fundamental
frequency is near the 5
th
bin and it’s skirt extends into
some or all of the first four bins, the fundamental energy
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
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
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

Larson Davis 824 Specifications

General

Brand	Larson Davis
Model	824
Category	Measuring Instruments
Language	English