NOTE: THIS DOCUMENT IS OBSOLETE, PLEASE CHECK THE NEW VERSION: "Mathematics of the Discrete Fourier Transform (DFT), with Audio Applications --- Second Edition", by Julius O. Smith III, W3K Publishing, 2007, ISBN 978-0-9745607-4-8. - Copyright © 2017-09-28 by Julius O. Smith III - Center for Computer Research in Music and Acoustics (CCRMA), Stanford University
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Audio Decay Time ()
In audio, a decay by is too small to be considered a practical ''decay time.'' In architectural acoustics (which includes the design of concert halls), a more commonly used measure of decay is '''', which is defined as the time to decay by dB.5.5 That is, is obtained by solving the equation
Using the definition of the exponential , we find
Thus, is about seven time constants. See where is marked on Fig. 5.5 compared with .