Dayton Audio OmniMic V2 Precision Measurement System - Manual (Page 39)

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Reverb/ETC
Index
Reverberation is a measure of how quickly sound reflections die down in a room, and will depend on
the frequency range of the sound, the size and shape of the room, what is in the room, and how the
room surfaces are constructed. Determination of RT60 can be made using this tool.
ETC stands for "Energy-Time Curve", which is a similar display, but which shows individual reflection
spikes more clearly to help in locating where they are coming from. This display is also able to
calculate "Speech Transmission Index" (STI) for auditorium and hall acoustics evaluations.
A third display option "Log IR" shows the dB level of the Impulse responses (like the one at the
bottom of the Frequency Response tab page, but in a decibel format), a very similar result to the ETC
in most cases.
These tests must be done while the sound system is playing the "long sine sweep" tracks of the
OmniMic Test Track CD . Use of other sound signals will not provide meaningful results.
Reverb (RT60)
OmniMic provides a graph of the reverberation decay curve. A properly done reverberation decay
curve will drop 40 decibels (dB) or more, relatively smoothly, from left to right. Using the mouse
cursor on the graph and the mouse button, you can obtain a measure of the RT60 value -- the time
needed for a reverberant field to die down by 60 decibels.