HP 8901B Operation And Calibration Manual page 280

Model 8901B Operation
Filter Characteristics
The individual filter characteristics are given below. The 3
dB
bandwidth is specified in the filter's
designation and is typically accurate to f3%.
High-Pass Filters:
50 Hz High Pass: Two-pole Butterworth, 1% flat to <200 Hz
300 Hz High
P a s s :
Two-pole Butterworth, 1% flat to <1 kHz
Low-Pass Filters:
3 kHz Low Pass: Five-pole Butterworth, 1% flat
to
> 1 kHz
15 kHz Low Pass: Five-pole Chebyshev, 1% flat to
>10 kHz
>20
kHz Low Pass: Nine-pole Bessel, 1% flat
to
>10 kHz. (When used with square
wave modulation, this filter typically overshoots <1%. This filter's 3
dB
point is typically
110 kHz.)
Filter Selection Does Not Affect Some Measurements
External Audio level, distortion, and SINAD measurements are unaffected by the audio filters.
Recommended Filter Selection
Because of the high sensitivity of the QM measurement to low-frequency audio (microphonics, hum,
etc.), use of the 50 Hz or 300 Hz low-pass filter is recommended. (Neither is switched in automatically.)
Audio Filters
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