13-8 824 Reference Manual 9/29/09
corrected by using coupler/earphone RETSPLs and
microphone or other such corrections to arrive at the dB HL
value.
Several different linearity
measurements can also be performed
as described in "Linearity RTA
Display" on page 13-10, "Linearity
FFT Display" on page 13-14and
"Flatness FFT Display" on page 13-
18.
Linearity evaluation can easily be performed by placing the
cursor on the audiometric presentation frequency, then
varying the hearing level output and monitoring the
measured level on the 824.
Similarly, cross talk measurements are performed with the
non-test earphone being measured, then comparing the test
earphone level to that measurement.
Any Level -a, -b and -c Displays
The Any Level Displays -a, -b and -c are accessed from the
SLM+RTA Live display by pressing the down arrow key
d
The Any Level -a display, shown below, displays Flat
weighted broadband SPL values for Fast and Slow
simultaneously.
The Any Level -b display, shown below, displays the Fast
SPL for A, C and Flat frequency weightings simultaneously.
Frequency is also available on the
FFT mode displays using a more
stable FFT frequency calculator.
Both the -a and -b displays show the output of the frequency
counter, showing Frequency and Period. The frequency
counter is a hardware count based on zero crossing;
significant amplitude is needed to ensure an accurate
reading.
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