18 Chapter 1
resolution measured in the width of a critical band, it follows that it must have fi nite
time resolution. This also follows from the fact that the membrane is resonant, taking
time to start and stop vibrating in response to a stimulus. There are many examples
of this. Figure 1.12 shows the impulse response. Figure 1.13 shows that the perceived
loudness of a tone burst increases with duration up to about 200 ms due to the fi nite
response time.
The ear has evolved to offer intelligibility in reverberant environments, which it does by
averaging all received energy over a period of about 30 ms. Refl ected sound that arrives
within this time is integrated to produce a louder sensation, whereas refl ected sound
that arrives after that time can be temporally discriminated and perceived as an echo.
Figure 1.12 : Impulse response of the ear showing slow attack and decay as a
consequence of resonant behavior.Figure 1.13 : Perceived level of tone burst rises with duration as resonance builds up.