There is a critical bandwidth beyond which adding noise power no longer increases masking

Evidence

Fletcher, however, did not find that the threshold of the signal increased by 10 dB per 10-fold increase in bandwidth! Rather, his experiment showed a very striking finding: For relatively narrow noise bandwidths, signal thresholds did increase as predicted by the power calculation. However, for all of the frequencies he tested, there was always a bandwidth beyond which increases in the masker bandwidth did not lead to further increases in masking. Fletcher dubbed this bandwidth the critical band. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 473

Categorization

• DEFINE: Introduces Fletcher’s concept of the critical band, a foundational idea in psychoacoustics.
• XREF: The critical band concept connects to cochlear frequency analysis and auditory filter models treated later in this book and in auditory neuroscience.