Room Acoustic Parameters

IRIS calculates room acoustic parameters in octave bands defined in ISO 3382-1:2009 (Performance spaces) [1] and ISO 3382-2:2008 (Reverberation time in ordinary rooms) [2].

Tip

Although IRIS displays only single octave band results on screen, you may export single or 1/3 octave band values to a spreadsheet.

Filter Details

  • IRIS uses a window-then-filter approach, as recommended by ISO 3382-1.
  • IRIS uses 6th order IIR filters (for octave band and one third octave band filtering).

List of Parameters

Parameter Description Standard
Decay Range (dB) The dynamic range of the decay curve (the backwards integrated impulse response. This is effectively the signal-to-noise ratio of the impulse response.  
EDT (s) Early decay time in seconds, evaluated from a best-fit regression line of the decay curve from 0 to 10 dB below the initial level, and extrapolated to 60 dB. ISO 3382-1
T20 (s) Reverberation time in seconds, evaluated from a best-fit regression line of the decay curve from 5 to 25 dB below the initial level, and extrapolated to 60 dB. ISO 3382-1,2
T30 (s) Reverberation time in seconds, evaluated from a best-fit regression line of the decay curve from 5 to 35 dB below the initial level, and extrapolated to 60 dB. ISO 3382-1,2
ζT20 (‰) Per mille deviation from perfect linearity of the decay curve from 5 to 25 dB below the initial level. ISO 3382-2
ζT30 (‰) Per mille deviation from perfect linearity of the decay curve from 5 to 35 dB below the initial level. ISO 3382-2
Curvature (%) A measure of non-linearity of the decay curve based on T20 and T30 ISO 3382-2
G (dB) Sound strength in decibels ISO 3382-1
G [0, 80) (dB) Early sound strength in decibels (from 0 to 80 ms)  
G [80, ∞) (dB) Late sound strength in decibels (from 80 ms to infinity)  
LF Early lateral energy fraction ISO 3382-1
LFC Early lateral energy fraction (cosine) ISO 3382-1
GLL Late lateral sound strength in decibels ISO 3382-1
C80 (dB) Clarity of music (80 ms integration time) in decibels ISO 3382-1
C50 (dB) Clarity of speech (50 ms integration time) in decibels ISO 3382-1
D50 Definition of speech (50 ms integration time) ISO 3382-1
Ts (ms) Centre time in milliseconds ISO 3382-1
STEarly (dB) Early stage support in decibels ISO 3382-1
STLate (dB) Late stage support in decibels ISO 3382-1

Spatial Parameters

When a 3D receiver is used, IRIS can determine the various lateral parameters (LF, LFC, GLL) directly. These parameters will be left blank for measurements with a mono receiver.

IRIS automatically aims a virtual lateral figure-of-8 microphone in post-processing. It detects the direct sound using the first 2 ms of the recorded impulse response and points the null of the virtual lateral microphone in this direction. This assumes the TetraMic is an upright position. The null direction is displayed on the PARAMETERS page alongside the lateral measures:

_images/lfparams.png

Note

Lateral fraction measurements with a TetraMic based IRIS system were evaluated using simulated sound fields in an anechoic chamber and found to be accurate to within one just-noticeable-difference of the true result. Details of the experiment were published in this paper.

[1]International Standard ISO 3382-1 Ed. 1, Acoustics – Measurement of room acoustic parameters – Part 1: Performance spaces (2009).
[2]International Standard ISO 3382-2 Ed. 1, Acoustics – Measurement of room acoustic parameters – Part 2: Reverberation time in ordinary rooms (2008).