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The primordial step in understanding acoustic behavior of a species is to describe
the characteristics of a specific emission, with regard to what types of sounds make up
the repertoire and what are the acoustical parameters features related to such sounds.
Sound emissions by odontocetes can be classified into two broad categories of frequency-varying continuous tonal sounds referred to as whistles and pulsed sounds
including broadband clicks including and burst sounds (Evans 1967). Depending on
the main objectives of a research, bioacousticians rely on some technologies to make
measurements in each broad category. Some examples are given below.
5.3.1 Whistles
The first method consists of visual inspection of spectrograms with a particular
emphasis on establishing categories in the shape of the whistle contour. Despite of
being very subjective, this method can be useful to determine if a particular contour
is unique within the repertoire or whether is a minor variation to another contour. In
order to specify a particular category of contour in which a whistle belongs to, we
have been using six general broad categories based on the slope of the whistle fundamental frequency and the number of inflection points, defined as a point at which
the slope of the contour reverses in direction:
1. Constant frequency: the frequency does not really remain constant over its duration, but has a minimum amount of frequency change (Fig. 5.4a).
2. Upsweep or ascending: the frequency is modulated with the instantaneous frequency increasing over duration and do not have any marked inflection points
(Fig. 5.4b).
3. Downsweep or descending: – the frequency is modulated with the instantaneous
frequency decreasing over duration and do not have any marked inflection points
(Fig. 5.4c).
4. Concave or ascending-descending: the frequency modulated with the instantaneous frequency initially increasing with time, followed by an inflection point
and an ending with the frequency decreasing over duration (Fig. 5.4d).
5. Convex or descending-ascending: the frequency is modulated with the instantaneous frequency initially decreasing with time, followed by an inflection point
and an ending with the frequency increasing over duration (Fig. 5.4e).
6. Sinusoidal or multiple: the frequency is modulated with more than one repetition
of a hill or a valley and the contour appearing somewhat like a sinusoidal signal
with at least two inflection points (Fig. 5.4f).
A more quantitative method involves extract various parameters of the fundamental frequency directly from the spectrogram: beginning (starting) frequency,
ending frequency, minimum frequency, maximum frequency, delta frequency, peak
frequency, center frequency, duration, number of inflection points, number or presence of break in contour and number or presence of harmonics.
A. Andriolo et al.
The primordial step in understanding acoustic behavior of a species is to describe
the characteristics of a specific emission, with regard to what types of sounds make up
the repertoire and what are the acoustical parameters features related to such sounds.
Sound emissions by odontocetes can be classified into two broad categories of frequency-varying continuous tonal sounds referred to as whistles and pulsed sounds
including broadband clicks including and burst sounds (Evans 1967). Depending on
the main objectives of a research, bioacousticians rely on some technologies to make
measurements in each broad category. Some examples are given below.
5.3.1 Whistles
The first method consists of visual inspection of spectrograms with a particular
emphasis on establishing categories in the shape of the whistle contour. Despite of
being very subjective, this method can be useful to determine if a particular contour
is unique within the repertoire or whether is a minor variation to another contour. In
order to specify a particular category of contour in which a whistle belongs to, we
have been using six general broad categories based on the slope of the whistle fundamental frequency and the number of inflection points, defined as a point at which
the slope of the contour reverses in direction:
1. Constant frequency: the frequency does not really remain constant over its duration, but has a minimum amount of frequency change (Fig. 5.4a).
2. Upsweep or ascending: the frequency is modulated with the instantaneous frequency increasing over duration and do not have any marked inflection points
(Fig. 5.4b).
3. Downsweep or descending: – the frequency is modulated with the instantaneous
frequency decreasing over duration and do not have any marked inflection points
(Fig. 5.4c).
4. Concave or ascending-descending: the frequency modulated with the instantaneous frequency initially increasing with time, followed by an inflection point
and an ending with the frequency decreasing over duration (Fig. 5.4d).
5. Convex or descending-ascending: the frequency is modulated with the instantaneous frequency initially decreasing with time, followed by an inflection point
and an ending with the frequency increasing over duration (Fig. 5.4e).
6. Sinusoidal or multiple: the frequency is modulated with more than one repetition
of a hill or a valley and the contour appearing somewhat like a sinusoidal signal
with at least two inflection points (Fig. 5.4f).
A more quantitative method involves extract various parameters of the fundamental frequency directly from the spectrogram: beginning (starting) frequency,
ending frequency, minimum frequency, maximum frequency, delta frequency, peak
frequency, center frequency, duration, number of inflection points, number or presence of break in contour and number or presence of harmonics.
A. Andriolo et al.