HP 8901B Operation And Calibration Manual page 283

Model
8901B
Operation
COMMENTS
Audio Range Effect on Distortion Measurements
The selected Audio Range has no effect on audio distortion or SINAD measurements.
When the audio range selected is too high for the level of the audio signal, the signal-to-noise ratio
will be low (no error is generated). (The output of MODULATION OUTPUT/AUDIO INPUT tracks
the displayed values.) When the audio range is too low for the audio signal level, Error
04
is generated.
(The output of the MODULATION OUTPUT/AUDIO INPUT
will
probably be clipped.) Depending
on the audio filtering and detector in use, Error
04 may
not be generated at exactly the nominal values
listed in the tables above.
Disabling Error 04 Inhibits Audio Autoranging
When Error
04 is
disabled (refer to Error Message Disable Control on page 3-233), the Modulation
Analyzer automatically ranges to a less sensitive range when the signal level requires, but it does not
range back when the audio level is reduced. This feature is used most often when modulation varies
widely with time (such as off-the-air demodulation of a broadcast signal).
Audio Range 3-185