Coding of auditory signals by intensity (loudness) should not be used.
Additional Information:
The range of intensities between the level required to ensure audibility and the level at which signals become aversive can be relatively narrow; the usefulness of this dimension for coding is therefore limited. If such coding must be used, no more than two levels should be defined. The signals should differ from each other by a minimum of 6 dB(A). The lower intensity should be about 10 dB(A) above the ambient noise level, and the maximum signal-to-noise ratio should be 10 dB(A) for most applications of sound intensity coding. It is recommended that sound intensity should be limited to a maximum of 95 dB(A), but that signal levels of 115 dB(A) may be used if considered absolutely necessary to achieve required attention-getting reliability for alarms indicating extreme danger. Whether this coding would be effective would depend on the frequency spectrum of the ambient control room noise and the frequency of the signal.