Biomedical Engineering Reference
In-Depth Information
4000
0.0
4.0
time (s)
8.0
Fig. 7.4.
A “composition” interpreted by the electronic syrinx. Each phrase is a
repetition of a syllable. In order to generate different syllables, the frequency of the
basic perturbation was changed, as well as the phase difference between the signals
emulating pressure and tension
(
t
) were used, and the phase differences between them were varied for the
different syllable types.
In order to generate different phase differences between
β
(
t
)and
(
t
),
a sinusoidal function generated by a function generator can be amplified
by means of different amplifiers such as the ones displayed in Fig. 7.5 to
produce
β
(
t
)and
(
t
). In this subsection we have focused on the generation
of signals corresponding to the labial oscillations in the syrinx, disregarding
the filtering that occurs in the tract. Notice that for some species, this can be
a good approximation to the real sound (as discussed in Chap. 3), although
not for all.
The first inset of Fig. 7.5 displays the amplifier used to generate the in-
struction
(
t
), emulating the gesture corresponding to changes in the tension
of the ventral syringeal muscle. By decreasing the variable resistance, the am-
plitude of the cyclic gesture was increased. This caused the synthetic sounds
to sweep a large range of frequencies. The potentiometer controls the constant
term in
(
t
), and therefore the average frequency of the vocalization.
−
+
−
+
−
−
Fig. 7.5.
These amplifiers can be used to generate two periodic functions with
a variable phase difference. An interesting way to drive this “electronic syrinx”
would be with a voltage measured by a pressure transducer connected to a cannula
inserted in an air sac, and a voltage obtained after rectifying and integrating a
voltage measured by microelectrodes inserted in the ventral muscles controlling the
frequency of the vocalization
