The basilar membrane yields only about 640 just-noticeable frequency steps end to end.

Evidence

The total length of the basilar membrane is 32 mm, indicated in the second linear scale. The third scale gives the number of just-noticeable steps measured by frequency modulation that can be achieved in proceeding from helicotrema to the oval window. All together, 640 steps based on just-noticeable frequency modulation can be added one after the other. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 933

Categorization

• QUESTION: Curious whether 640 JND steps is frequency-modulation specific or generalizes across loudness and other dimensions measured the same way.