upper band limit of half the incoming sample rate, and the
22 kHz-QPK selection is the same as in the analog domain.
.
AVERAGE - The ‘Average’ selection allows the same
band-limiting filters as UN-WTD. Instead of displaying each
reading as it is obtained, the average of the eight most recent
readings is displayed. This is used to reduce digit bobble,
especially when testing distortion in the presence of noise and
flutter from analog tape recorders.
.
WTD – The ‘weighted’ selection allows selection of a variety of
weighting filters with a selectable lower band limit. The lower
center soft key selects the lower band limit (<10 Hz or 400 Hz).
The lower right soft key selects among the following weighting
filters:
.
IEC-A – A-weighting filter per IEC 179, true RMS detector
.
CCIR-1k – Weighting per CCIR-468, true RMS detector
.
CCIR-2k – Weighting per CCIR-468, but with 0 dB gain
point at 2 kHz rather that 1 kHz, true RMS detector
.
CCIR-QPK – Weighting per CCIR-468, quasi-peak detector
.
CCIR-ARM (analog only) – Weighting filter shape per
CCIR-468, but with 0 dB gain point at 2 kHz rather that 1
kHz, average-responding detector per Dolby Bulletin 19/4
.
AUX1 (analog only) – Weighted with optional weighting
filter installed in slot 1. If there is no filter in slot 1, the
display will read ‘NO AUX1’ and no filter is selected.
.
AUX2 (analog only) – Weighted with optional weighting
filter installed in slot 2. If there is no filter in slot 2, the
display will read ‘NO AUX2’ and no filter is selected.
Selection of the proper band-limiting filters is of critical importance in
THD+N measurements. The dominant signal is often wideband
noise when measuring high-quality audio devices, so the specified
band-limiting filter must be used if measurements are to correspond to
manufacturer’s specifications.
The 80 kHz lowpass filter is the most commonly used, since it
eliminates wideband noise while passing the 2nd and 3rd harmonics of
frequencies within the audio band.
& The shapes of the
weighting filters are
shown on page 6.
4 Functions
THD+N (Total Harmonic Distortion plus Noise) Function Descriptions
4-10 ATS-1 Dual Domain User's Manual
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