Masking shifts thresholds upward and may alter just-noticeable sound changes at all levels.

Evidence

Often when listening to music or speech we cannot listen in the quiet. Additional tones or noises influence just-noticeable sound changes. Such influences must occur because the threshold in quiet is shifted upwards to become a masked threshold. The important question is whether additional sound that produces partial masking influences just-noticeable sound changes only in the neighbourhood of the masked threshold or also at higher levels. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1103

Categorization

• QUESTION: Whether partial masking alters just-noticeable sound changes above the masked threshold is left as an open research question worth following across the later chapters.