Larson Davis System 824, Справочное руководство

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12-6 824 Reference Manual 11/8/00
The FFT measurement can be tailored with a number of vari-
ables. To enter the menu where these are selected, press the
check key
.
You can now use the arrow and check keys to change the
FFT gain (-20 to +50 in 10 dB steps), bandwidth (200, 500,
1K, 2K, 5K, 10K, and 20K hertz), and window (Hanning,
rectangular or flat top).
To read a level in dB (re. 20 micropascals), place the cursor
on the frequency of interest and read the frequency and
value on the left hand side of the screen. In this mode, levels
must also be corrected by using coupler/earphone RETSPLs
and microphone or other such corrections to arrive at dB HL
value.
Noise measurements can also be performed in the FFT
mode, especially the narrowband noise frequency cut-offs
and the white noise flatness.
THD (Total Harmonic Distortion)
To access the THD screen, press the VIEW key
, select
FFT with the up/down arrows
and press the right
arrow
key.
This will display the sub-menu of the FFT screen.