Beyond threshold, masker and signal levels rise one-for-one in decibels

Evidence

Intensity effects. Increasing the masker dB SPL level increased the signal level necessary for detection. Figure 3–6 shows that once masking occurred (that is, once the masker was sufficiently powerful to mask the signal), a 10 dB increase in masker led to a 10 dB increase in masking. For example, at 1000 Hz, the 20 dB SPL masker was associated with a 40 dB SPL threshold, and the 30 dB SPL masker caused threshold to be 50 dB SPL. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 454