OPTICOM OPERA - V 3.5 User Manual page 105

C H A P T E R 5 : W I D E B A N D A U D I O Q U A L I T Y T E S T I N G
Figure 5.17: Select Signal window of the NMR diagram type
Figure 5.18: The NMR diagram
Masked Threshold
A signal that is clearly audible can be completely inaudible in the presence of
another signal, the masker. This effect is called masking and the masked signal
is called maskee. There are two situations that have to be distinguished -
simultaneous masking and temporal masking. In case of simultaneous masking
the masker and the maskee are present at the same time and are quasi-
stationary. In case of temporal masking the masker and the maskee are present
at different times [ITUR1387]. Both situations are taken into consideration in the
masked threshold diagram.
As Figure 5.19 shows, choose between the masked threshold, the reference
spectrum and the noise spectrum (spectrum reference – spectrum test) of the
right and left channel. The horizontal axis of the diagram is a Bark scale, the
vertical axis is scaled in dB[SPL] (see Figure 5.20).
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