note # 12
Reverberation Time computation by using the reverse-time integrated
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:
M.R. New Method of Measuring Reverberation Time
J. Acoust. Soc. Am.1965
M.R. Integrated-Impulse method measuring sound decay
without using impulses J. Acoust. Soc. Am. Vol. 66(2)
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).
1 - Room Impulse Response
2 - Schroeder Plot from data in figure 1
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
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.
3 - RT30 computed from Schroeder Plot in figure 2
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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