SP395 SoundPro Audio Integrator Form7492 Operation Manual
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APPENDIX C – ANSI Balanced Noise-Criterion Curves
Simple SPL measurements do not represent the background noise our ears hear. Because our ears
are less sensitive to low frequency noise than to high frequency noise, noise levels at higher
frequencies must be given more weight than levels at lower frequencies. The result is a set of
curves called Noise Criterion or NC curves. The curves are arbitrarily numbered for easy
reference. The Noise Criteria (NC) rating of a room is the number of the lowest curve that is not
exceeded by any of the noise in the room. To determine an NC rating, the noise levels at 8
different octave band frequencies are measured and compared to the Noise Criteria curves.
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