Delay Lines and Effects
67
-20
-15
-10
-5
0
5
10
15
20
0.1
1
10
magnitude [dB]
frequency [kHz]
100
130
160
190
220
250
0
5
10
15
20
25
30
0.1
1
10
group delay [samples]
frequency [kHz]
250
220
190
160
130
100
Figure 10: Magnitude and Group Delay responses of the block responsible for
head shadowing and ITD (F
s
= 44100Hz). Azimuth ranging from ear to ear+
150
.
where and are azimuth and elevation, respectively (see fig. 10 of the ap-
pendix C). The echo should also be attenuated as the source goes from frontal
to lateral position.
Finally, the pinna provides multiple reflections that can be obtained by
means of a tapped delay line. In the frequency domain, these short echoes trans-
late into notches whose position is elevation dependent and that are frequently
considered as the main cue for the perception of elevation [48]. A formula for
the time delay of these echoes is given in [19].
The structural model of the pinna - head - torso system is depicted in Fig. 11
with all its three functional blocks, repeated twice for the two ears. The only
difference in the two halves of the system is in the azimuth parameter that is
for the right ear and - for the left ear.
monoaural
input
left output
channel
RIGHT
LEFT
right output
channel
head shadow and ITD
shoulder echo
shoulder echo
head shadow and ITD
pinna reflections
pinna reflections
,
-,
,
-,
-
Figure 11: Structural model of the pinna - head - torso system