Sound absorption of an interior space is tested by measuring the rate of sound level reduction after a noise source that has been used to fill the room with sound is abruptly stopped. The measurement result is called Reverberation Time or RT-60, equivalent to the number of seconds that would be needed for the sound level to decay by 60 dB.
The Virtual Instrument shown above analyzes the test results in specific frequency bands to identify room response characteristics. The left chart shows how a usable portion of the curve is manually selected to eliminate record portions that are not part of the linear decay. The right chart shows how the manually selected start and end points maximize the dB range (span) and minimize the error (mse) of the linear approximation fit to the data.