NOTE: this function is now available from the IoSR Matlab Toolbox as iosr.acoustics.irStats.
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Calculate RT, DRR, Cte, and EDT for impulse response file
RT = IR_STATS(FILENAME) returns the reverberation time (to -60 dB)
using a method based on ISO 3382-1:2009. The function uses reverse
cumulative trapezoidal integration to estimate the decay curve, and a
linear least-square fit to estimate the slope between 0 dB and -60 dB.
Estimates are taken in octave bands and the overall figure is an
average of the 500 Hz and 1 kHz bands.
FILENAME should be the full path to an audio file or the name of an
audio file on the Matlab search path. The file can be of any format
supported by the AUDIOREAD function, and have any number of channels;
estimates (and plots) will be returned for each channel.
The function returns a 1xN vector of RTs, where N is the number of
channels in the audio file.
The function determines the direct sound as the peak of the squared
impulse response.
[RT,DRR] = IR_STATS(FILENAME) returns the direct-to-reverberant-ratio
DRR for the impulse; DRR is the same size as RT. This is calculated
in the following way:

DRR = 10 * log10( X(T0-C:T0+C)^2 / X(T0+C+1:end)^2 )

where X is the approximated integral of the impulse, T0 is the time of
the direct impulse, and C=2.5ms [1].

[RT,DRR,CTE] = IR_STATS(FILENAME) returns the early-to-late index CTE
for the impulse; CTE is the same size as RT. This is calculated in
the following way:

CTE = 10 * log10( X(T0-C:T0+TE)^2 / X(T0+TE+1:end)^2 )

where TE is 50 ms.

[RT,DRR,CTE,CFS] = IR_STATS(FILENAME) returns the octave-band centre
frequencies CFS used in the calculation of RT.

[RT,DRR,CTE,CFS,EDT] = IR_STATS(FILENAME) returns the early decay
time EDT, which is the same size as RT. The slope of the decay curve
is determined from the fit between 0 and -10 dB. The decay time is
calculated from the slope as the time required for a 60 dB decay.

... = IR_STATS(...,'PARAMETER',VALUE) allows numerous
parameters to be specified. These parameters are:

'graph' : {false} | true
Controls whether decay curves are plotted. Specifically, graphs
are plotted of the impulse response, decay curves, and linear
least-square fit for each octave band and channel of the audio
file. If the EDT output is specified, the EDT fit will also be
plotted.
'te' : {0.05} | scalar
Specifies the early time limit (in seconds).
'spec' : {'mean'} | 'full'
Determines the nature of RT and EDT outputs. With spec='mean'
(default) the reported RT and EDT are the mean of the 500 Hz
and 1 kHz bands. With spec='full', the function returns the
RT and EDT as calculated for each octave band returned in
CFS; RT and EDT have size [M N] where M=length(CFS).
'y_fit' : {[0 60]} | two-element vector
Specifies the decibel range over which the decay curve should
be evaluated. For example, 'y_fit' may be [-5 -25] or [-5 -35]
corresponding to the RT20 and RT30 respectively.
'correction' : {0.0025} | scalar
Specifies the correction parameter C (in seconds) given above
for DRR and CTE calculations. Values of up to 10 ms have been
suggested in the literature.

Octave-band filters are calculated according to ANSI S1.1-1986 and IEC
standards. Note that the OCTDSGN function recommends centre frequencies
fc in the range fs/200 < fc < fs/5.

The author would like to thank Feifei Xiong for his input on the
correction parameter.

References

[1] Zahorik, P., 2002: 'Direct-to-reverberant energy ratio
sensitivity', The Journal of the Acoustical Society of America,
112, 2110-2117.

See also AUDIOREAD, OCTDSGN.