AudioControl SA-3052A, Руководство по эксплуатации

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SA-3052A Owner’s Manual
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Chapter 1 - Introduction
ANSI Filter Design
A real-time analyzer works by dividing the audio spectrum up into equal bandwidth
parts using a set of calibrated (usually) bandpass filters. Then the output of each filter is
displayed on some sort of level indicator: LED matrix, Video display, LCD, etc.
The American National Standards Institute (ANSI) oversees the establishment and
maintenance of various engineering standards in conjunction with the International Stan-
dards Organization (ISO) in Europe. These two standards organizations have established
standards for the performance of the bandpass filters used for acoustical measurement
purposes.
For one-third octave analyzers, there are two classes of filters allowed by ANSI.
These are Class II, and Class III. Class I is reserved for octave bandwidth analyzers.
Class III filters are the hardest to design and manufacture and are usually only found on
the most expensive (read unaffordable) analyzers. Class II filters, are easier (not easy, just
easier) to design and manufacture than Class III filters. Any real-time analyzer intended
for serious measurement work will use filters that at least meet Class II standards.
The filters used in the SA-3052A analyzer meet or exceed the standards specified by
ANSI for a Class II, Type E filter set. Simply, they are very, very good but still affordable.
Figures 1.1 and 1.2 show two different one-third octave filters. Figure 1.1 is repre -
sentative of those found in most analyzers. Figure 1.2 is an actual filter used in the
SA-3052A. Note the difference in the response away from the center frequency. The
inferior filter’s broad response characteristic translates to potential measurement errors at
frequencies removed from the band-center and undesirable interaction between adjacent
frequency bands.
Figure 1.1. A non-measurement quality one-third octave filter
Figure 1.2. A measurement quality one-third octave filter