The commonly used A-weighting frequency response is used to allow for the frequency response of the human ear – it would not necessarily be appropriate when considering the impact of noise on other animals.
Although noise is quantified in terms of dB(A), its content can have an additional and profound effect on both the subjective loudness and the degree of annoyance/nuisance that can be attributed to the noise.
Currently, these effects are referred to as 'intrusive or dominant characteristics' and include tonality, impulsiveness, modulation and low frequency. These characteristics are defined in the Noise Measurement Procedures Manual for the purpose of adjusting measured dB(A) levels to allow for the increased loudness and/or annoyance caused by such characteristics.
This adjustment scheme is not perfect. Very complex sounds, such as animal grows or sounds that include many discrete tones, may not be adequately evaluated.
The information content of a noise can profoundly influence its degree of annoyance. A neighbour slightly annoyed by a farmer's irrigation pump will be relieved when the pump fails in the middle of the night. The farmer, on the other hand, will be immediately concerned if he hears the pump noise suddenly stop.