ABSTRACT
Air temperature, humidity, and atmospheric pressure change how sound is absorbed over distance. This atmospheric absorption has the strongest effect on high frequencies and so is often modeled as a low-pass filter as one component of the overall attenuation settings for a sound instance. This chapter explores using the atmospheric features of air temperature and humidity to provide a systematic way of setting a low-pass filter cutoff for sound propagation. The frequency response of atmospheric absorption is mostly flat out to a point where the frequencies begin to fall off. The falloff becomes nearly linear on a logarithmic scale, so it shares key traits with the Butterworth filter which is flat in the passband and also falls off linearly on a logarithmic plot. For fast moving objects, the filter cutoff may need to be interpolated with a slight delay over time or smoothing function to avoid sudden jumps in the filter cutoff.
