Influence calculated from calibrated measurement

If this setting is selected and the measurement is performed using MLS, the background noise in the actual measurement is automatically taken into account when computing the MTF, MTI and speech transmission indices [D. Rife, “Modulation Transfer Function Measurement with Maximum-Length Sequences”, (JAES), vol. 40, No. 10, pp 779-790, 1992 October]. Modulation effects of both reverberation and background noise are taken into account in a single measurement. For the results to be accurate, the speech and noise levels at the measurement microphone must be representative, and no noise-reducing averaging must be employed. The speech spectrum and level can be obtained by using a calibrated source.

In addition to selecting MLS as output signal, it is important that pre-emphasis is turned on. Set this from Measurement->Settings... as shown below.

We see from the figure above that MLS is selected and emphasis Pre, output only is selected. As emphasis filter STI/RASTI is selected. This will give correct results for STI and RASTI. Select the filter options STIrMale to get correct results for STIrMal and select STIrFemale to get correct results for STIrFem.

Note: If truncation of the impulse response is set in the Advanced Calculation Options, it is not used when Correction using background noise in measurement is selected because the whole impulse response must be included to get correct result.

Note: In this case the computation of other room acoustics parameters (including EDT and D50 in the speech parameter option) must be treated with outmost care, since the directivity of the speech source is different from a normal room acoustics measurement loudspeaker, and the pre-filtering that is supposed to be applied changes the impulse response.