Critical Bands

A tone at a certain frequency will create a disturbance on the basilar membrane (BM) which will spread over a certain length on either side of the point of maximum displacement.

The nerve endings in the BM are excited over this narrow region, called the critical band, which correspond to a range of frequencies above and below the frequency of the incoming sound.

The critical band (bandwidth) varies with frequency:

• it is about 90 Hz wide for a sound frequency of 200 Hz, increasing to a width of about 900 Hz for a 5000 Hz sound.
• this corresponds to a region on the BM of essentially 1.2 mm (covering a range of about 1300 receptor cells).