Larson Davis SoundAdvisor 831C Reference Manual page 152

FIGURE 18-9
FFT Live Display Elements
1.
Press the up button (
frequency range. The 831C allows zooming from
the configured number of lines up to a 1:1
correspondence between displayed lines and
FFT lines. When zoomed in on a 1:1 ratio, the
level indicator ("@ max") changes to show that
the displayed level is no longer the max value of
multiple overlapping levels, but the max value of
a single level at the cursor.
2.
Press the left or right button (
the Manual cursor. To enable Max-Tracking or
Harmonic cursors, press Menu (
choose Cursor Type. For additional detail, see
Editing the Cursor on page 147.
3.
When you highlight Hold and press Enter
the graph pauses for your examination, while the
measurement continues. Select Resume to un-
pause the graph.
4.
To edit the y-axis graph scale, press Menu (
and choose Adjust Graph. Units displayed for the y-
axis depends on the transducer; the default is
"decibel" for a mic, or "g" when you selected a
transducer other than a mic. You may customize the units during the measurement setup, as shown in 18.1
Preparing the Equipment.
//*
SoundAdvisor Model 831C
8
) to Zoom in on a
46
) to advance
/*/
), and
5
/*/
Live Data On the THD Tab
FIGURE 18-10
//*
Use the right softkey (
tab.
The Total Harmonic Distortion tab displays
fundamental, and harmonic amplitude, and the
percent distortion for each. The percentages for
THD+N (Total Harmonic Distortion + Noise) and
THD are methods of examining the energy
dispersion of the measured signal.
The percent distortion shows how much of the
signal energy is based in the fundamental
frequencies, and may be an indication of how
inefficient a signal may be.
Editing the Cursor
When viewing Live data you can select the cursor type. Choose Menu (
Type on the 831C, then select Manual, or Max-Tracking. Each can be displayed with or
without harmonics. Editing the cursor is also shown in Figure 18-9. Use the left and right
46
buttons ( ) to advance the Manual cursor and investigate tone details in the graph.
1.
,
4.
),
) to select the THD
Making the FFT Measurement
2.
3.
/*/
 Cursor
)
147