Table of Contents
Advertisement
AM5(e) Classic Instruction Manual
8.
CCITT NOISE WEIGHTING FILTERS
FOR AM5e CLASSIC
This Section describes the filters that are supplied with the AM5e
Classic. Except for the 60 Hz filter, which is common to the AM5
and the AM5e Classic, the filters described comply with CCITT
Recommendations and are used for noise measurements
described in Section 6 (sub-sections 6.3 through 6.7). The front
panel area for FILTER is shown to the right. Default selections are
shown by shading.
NOTE: The default indication for PSHO does not apply to the default
MEASURE LEVEL FREQ selection. The PSHO default will come on when any MEASURE
noise function is selected, then go out when MEASURE LEVEL FREQ or L/F UNWTD are
selected. No noise weighting filter can be selected while LEVEL FREQ or L/F UNWTD are
selected.
A low-pass filter (L/F UNWTD can be selected by the MEASURE key for
level/frequency measurements only. The response of this filter rolls off frequencies
above 15 kHz (refer to 8.3).
A 995 Hz to 1025 Hz notch filter is automatically switched in when measuring noise
with (1004 Hz) tone, impulse noise with tone, or signal-to-noise ratio (NOISE W/T,
IMP NOISE W/T, S/N RATIO). This filter is not illustrated.
8.1
NOISE WEIGHTING FILTERS
Noise weighting filters are selected by each press of the left FILTER key (bottom to top,
left to right). Other than the lighted LED, there are no displays or parameters
associated with the FILTER selections.
Only one noise weighting filter can be selected at a time, but the 60 Hz filter (8.2) may
be selected in addition to the noise weighting filter to eliminate power interference.
The noise weighting selections are summarized below, and the curves for the filters are
shown in the referenced figures. The UNWTD and SWTD filters permit selection of
RMS or Quasi-Peak (Q-PEAK) detectors. The other filters use RMS detection.
FILTER
DESCRIPTION
SELECT
PSHO
Psophometric Bandpass
UNWTD
Sound Un-Weighted low- pass, high-
Q-PEAK
pass with Quasi-Peak detection.
SWTD
Sound-Weighted low-pass, high-
Q-PEAK
pass with Quasi-Peak detection.
UNWTD
Same filter as UNWTD Q-PEAK but
RMS
with RMS detection
SWTD
Same filter as SWTD Q-PEAK but
RMS
with RMS detection
2 kHZ
Bandpass 750 – 2300 Hz
FLAT
WIDE
20 Hz to 120 kHz (-120)
20 Hz to 160 kHz (-200)
November 19, 1997
(18–0047)
AM5e CLASSIC FILTERS
RECOMMEN-
DATION
CCITT P.53
CCITT J.16
CCITT J.16
CCITT J.16
CCITT J.15
CCITT O.71
Page 8-1
UNWTD
WIDE
RMS
2kHz
SWTD
Q PEAK
SWTD
0
1
UNWTD
RMS
Q PEAK
1 1
0 0
PSHO
60 Hz
1 1
0 0
1 1 1 1
0 0 0 0
1 1
0 0
FI LTER
CURVE
Figure 8-1
Figure 8-2
Figure 8-3
Figure 8-2
Figure 8-3
Figure 8-4
—
Figure 8-5
—
Figure 8-6
Advertisement
Table of Contents
