Digital Sound & Music: Concepts, Applications, & Science, Chapter 4, last updated 6/25/2013
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discernable. Typically, reverberation time is defined as the time it takes for the sound to decay
in level by 60 dB from its direct signal.
Figure 4.17 Sound reflections and reverberation
Single, strong reflections that reach the ear a significant amount of time about 100 ms
after the direct signal can be perceived as an echo essentially a separate recurrence of the
original sound. Even reflections as little as 50 ms apart can cause an audible echo, depending on
the type of sound and room acoustics. While echo is often employed artistically in music
recordings, echoes tend to be detrimental and distracting in a live setting and are usually avoided
or require remediation in performance and listening spaces.
Diffusion is another property that interacts with reflections and reverberation. Diffusion
relates to the ability to distribute sound energy more evenly in a listening space. While a flat,
even surface reflects sounds strongly in a predictable direction, uneven surfaces or convex
curved surfaces diffuse sound more randomly and evenly. Like absorption, diffusion is often
used to treat a space acoustically to help break up harsh reflections that interfere with the natural
sound. Unlike absorption, however, which attempts to eliminate the unwanted sound waves by
reducing the sound energy, diffusion attempts to redirect the sound waves in a more natural
manner. A room with lots of absorption has less overall reverberation, while diffusion maintains
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