AudioControl SA-3051, Руководство по эксплуатации

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SA-3051/SA-3052 Operation Manual
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 indi -
cator: LED matrix, Video display, LCD, etc.
The American National Standards Institute (ANSI) oversees the establishment and maintenance of vari-
ous engineering standards in conjunction with the International Standards 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-3051/SA-3052 analyzer meet or exceed the standards specified by ANSI for a
Class II, Type E filter set.
Figures 1.1 and 1.2 show two different one-third octave filters. Figure 1.1 is representative of those found
in most lower-cost analyzers. Figure 1.2 is an actual filter used in the SA-3051/SA-3052. Note the dif -
ference 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
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