Frye FONIX 7000 User Manual
Page 47
General Operation
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Figure 2.3.2.2—Example of IM distortion
2.3.2.3 Composite filter
There are two main types of composite filters (also known as “speech weight-
ing”): ICRA and ANSI. They differ in the speech spectrum they use.
The ANSI filter, taken from the ANSI S3.42 standard, rolls off the high frequen-
cies at a rate of 6 dB per octave, starting with a 3 dB drop at 900 Hz. The ICRA
filter uses the ICRA speech spectrum developed by the International Collegium
of Rehabilitative Audiology. The ICRA spectrum is based on the Long Term
Average Speech Spectrum (LTASS) and rolls off the high frequencies more rap-
idly than the ANSI spectrum. Figure 2.3.2.3 shows a comparison of the spectra.
In general, we recommend using the ANSI speech weighting for Composite and
Digital Speech measurements.