Application
note # 12 
Sample
Champion

Reverberation Time computation by using the reversetime integrated
Impulse Response
Reverberation
time measurements can be made by using the MLS method and a
peculiar analysis technique, commonly called Schroeder Integration.
This way of measuring sound decay was introduced firstly by
M.R. Schroeder in two historical articles:
 Schroeder
M.R. New Method of Measuring Reverberation Time
J. Acoust. Soc. Am.1965
 Schroeder
M.R. IntegratedImpulse method measuring sound decay
without using impulses J. Acoust. Soc. Am. Vol. 66(2)
1979
The reverse time integration transforms the normal Room Impulse
Response (fig. 1) into a decay plot (fig. 2) where it is possible
to evaluate the decay time and consequently the reverberation
time (60 dB decay).
Figure
1  Room Impulse Response
Figure
2  Schroeder Plot from data in figure 1
The
decay plot can be noise compensated, for obtaining a curve more
close to a line (the noise decaying is exponential but the Y
axis scale is in dB). The Room Acoustics plugin can optionally
apply the noise compensation to the Schreoder Plot (see Application
Note #11 for some guidelines about using the noise compensation
option).
Figure
3 shows the computation of RT30 by using the Room Acoustics
plugin of Sample Champion. RT30 is the reverberation time of
the room (the time required for a sound decaying of 60 dB) evaluated
over a 30 dB decay range in the Schroeder Plot (from 5 to 35
dB), using linear regression techniques.
Figure
3  RT30 computed from Schroeder Plot in figure 2
The
value (written in the right lower corner of the graphic screen)
is 2051.85 ms (r=0.9909). A value of r close to 1 indicates
a good superposition of the regression line with the decay plot.
The Impulse Response can be band filtered for obtaining the
reverberation value in a specific band, by using the Room Acoustics
plugin. See Application Note #11
about the computation of other acoustical parameters from a
Room Impulse Response.
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