audibilityofanecho

In this first step we created an impulse response by simply adding impulses to a vector which contains direct sound plus one (broadband) reflection with a certain delay and level relative to the direct sound.

Here the interesting aim is on one hand to vary the reflection delay time and level, in order to see the influence of these effects on the perceived sound, and on the other hand to convolve this impulse reponse to a speech and drums sounds.

As one can guess easily, the impulse sound is affected very quickly by the reflection path. Even a delay time of about 0.005 is detectable (with a reflection level of 0.5 which corresponds to -6 dB), and this has the same state if we take a lower reflection level.

But both for the speech or the music the delay time and the reflection level are really important.

Speech

As one could hear with the sounds on the right side of the page, an echo is detected from a low value of the reflection level (0.5 or -6 dB) if the delay time is fixed at 80ms. According to the Figure 5.12, this result is normal since even a reflected sound of 10 dB less than the direct sound is detected. Again the study agrees with our measurement since for a delay time of 40ms, the echo is detected only if the reflection level is above 1 (same level than the dırect sound).

Adding a reflected sound which is not high enough to be perceived as an echo changes a bit the original sound. It seems that this latter is perceived as a more metallic sound.

Music

At first one could guess that since drums beats are made of several "long" impulse responses following one another (transient sounds), the reflected sound will be easily heard in comparison to the speech which is something continue.

The experiment shows that for the same delay time (40ms) the detection of the reflected sound is made above a reflection level of 0.4 (around -7 dB), and for a delay time of 80ms the reflection level should be around 0.3 (around -9 dB). This small difference between 40ms and 80ms may be due to the slow decay of each drum beat.