Click here to purchase the entire book in PDF format. High-frequency content As we saw in Section 3.2.3, air has a tendency to absorb high-frequency information. Over short distances, this absorption is minimal, and therefore not detectable by humans. However, over long distances, the absorption becomes significant enough for us to hear the difference. Of course, we are again assuming that we are familiar with the sound source. If you don't know the normal frequency balance of the sound, then you won't know that the high end has been rolled off due to distance.