Frequency Weighting (A, B and C-weighting)

The sensitivity of the human ear varies with frequency and with the sound level. In other words:

For the same physical energy, the intensity of a sound (loudness) is perceived differently by the human ear if the frequency is different.
For the same frequency, when the physical energy of a sound evolves linearly, the perceived intensity of this sound (loudness) does not evolve linearly.

For these reasons, the notion of Frequency Weighting has been introduced and standardized. The most common examples are A, B, and C-weighting.

The IEC61672 standard defines weighting functions (formulas) to calculate the A, B and C weighting at any frequency. For a given frequency f in Hz, the A, B and C linear weights are calculated using these equations:

These are the formulas used in Ansys Sound: Analysis and Specification when the weight at a given frequency is required. In the context of weighting time signals (temporal sound pressure level) using weighting filters, Ansys Sound: Analysis and Specification uses filters that are compliant with the filter shapes specified in the IEC 61672 standard for A, B and C-weightings.