Masking

Figure 1: Sound propagates into the ear canal (outer ear) before transmitting the vibration to the eardrum and ossicles of the middle ear (malleus, incus and stapes). The oval window (touching the other tip of the stapes) then receives and sends the oscillations to the cochlea (inner ear) [4].

Figure 2: Unrolled basilar membrane, with the frequency values (in Hertz) aligned with the corresponding distances from the oval window. Notice how the range of frequencies covered by an identical small segment of basilar membrane near the oval window (e.g., from 6000 to 8000 Hz) is much bigger than it is near the helicotrema (e.g., from 150 to 200 Hz) [7].

Figure 3: This diagram shows the relation between the basilar membrane excitation pattern for a sine wave signal (S) and a narrow-band noise masker (B) at different frequency and level relations between the two. It demonstrates that lower-frequency maskers have more of a masking effect than do higher-frequency maskers. The overlap between the two excitation patterns is shown by the hashed region. Notice that a masking noise at a lower frequency masks the signal more at higher levels than does a masker at a higher frequency than the signal.