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Air Absorption

As sound travels through the air it loses energy, primarily at high frequencies. The greater the distance between the source and listener the greater the attenuation.

Model

Air absorption is implemented as a 1st order IIR filter1 with coefficients \(b0 = e ^ {\frac{-d \cdot f_s} {7782 \times c}}\) and \(a1 = b0 - 1\), where \(d\) is the distance the sound has traveled through the air, \(f_s\) is the sampling frequency and \(c\) is the speed of sound in air. This allows the distance to be interpolated at runtime and the filter parameters updated.

Air absorption 1st order IIR filter
Figure 1: Air absorption 1st order IIR filter.

  1. Grimm G, et al. "Implementation and perceptual evaluation of a simulation method for coupled rooms in higher order ambisonics," Proc. of the EAA Joint Symposium on Auralization and Ambisonics, Berlin, Germany. 27-32, 2014. ↩