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Implemented Model for ATH

From [6] I take the approximation of the curve in figure 1 as


where ATH(f) denotes the ATH in dB, and f is the frequency in Hz. The problem in digital audio coding, is that it is not known at what absolute level the sound will be played. One common solution is to set the lowest point on the curve in (6) to be equal to the sound pressure level of a sine with amplitude tex2html_wrap_inline968 LSB. In the coder, 16-bit samples with normalized amplitude to tex2html_wrap_inline968 are used. Thus, the smallest possible sine has amplitude tex2html_wrap_inline972 , and has a power of tex2html_wrap_inline974 . In experiments, though, that setting did not seem to ``keep'' high enough frequencies for transient sounds, so the model was chosen as ATH'(f) = ATH(f)-114.

Bosse Lincoln
Sat Mar 7 16:27:43 PST 1998