9/29/09 AUD (Optional) 13-19
The operation and menus for this display are the same as
Linearity FFT; please refer above for operation instructions.
THD Display
The THD display, shown below, is accessed from the
Flatness FFT display by pressing the down arrow key d
.
The THD display provides harmonic distortion
measurements of an audiometer and its phones. The FFT
capabilities of the 824 are used to measure the fundamental
level, fundamental frequency and harmonics. THD data is
output in dB down from the fundamental level and in
percent. The display also shows the level and frequency of
the fundamental. An asterisk following a THD percentage
indicates that influences of system noise floor are present.
Results are reported in dB down difference and units of
percentile. The dB down difference is calculated by
subtracting the harmonic level from the fundamental level.
The percentage is equal to one hundred times ten raised to
THD+n percentile
Harmonic
percentiles
4th and higher percentiles
Fundamental frequency
THD+n dB down
Harmonic dB down
4th & higher harmonics
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