FONIX® 8000 - Frye Electronics

General Operation 39
2.3.2.3 Composite filter
There are two main types of composite filters (also known as “speech weighting”):
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 frequencies
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 rapidly
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.
Figure 2.3.2.3—Comparison of the ICRA shape and the ANSI shape
2.3.2.4 Composite type
There are two types of the traditional Composite signal available on the FONIX
8000 Test System. They are known as “Standard” and “Chirp.” The two signals
differ in the manner that their phase is generated, and this difference has an
impact on the crest factor of the signals. The crest factor of a waveform is the
ratio of its highest amplitude to its RMS amplitude. Human speech is often
referred to as having a 12 dB crest factor.