Monotic in-phase masking-level difference is frequency-independent from 250 to 4000 Hz

Evidence

The second example deals with the effect of signal frequency. It describes, in other coordinates, results that are found in threshold measurements, in which a monaural sinusoidal signal is added either in phase or 90° out-ofphase to a continuous masker of the same frequency. The masker is presented binauraUy and is always identical in each ear. The frequency is varied from 63 to 4000 Hz. Figure 15.11 shows the transformed data at LM = 50 dB (left) and 70 dB (right). Results for the condition with in-phase addition of the signal are shown by the line labelled “fJ.L”, which gives the value of fJ.L = 20 log (1 + PT I PM) shown on the outer ordinates in dB and on a logarithmic scale. As a first approximation, the value of fJ.L is independent of frequency between 250 and 4000 Hz but rises slightly towards lower frequencies. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1699