The acoustic structure of
animal sounds may be influenced by a number of
factors, such as the context or the motivational state
of the caller. Due to the mechanisms of sound
production, however, all sounds invariable transmit
information about physical properties of the caller.
In mammals, sound is produced by airflow generated in
the lungs that drives oscillations of the vocal tract
folds located in the larynx. The source signal then
passes the vocal tract, which acts as a
bandpass-filter allowing a narrow range of frequencies
to pass (‘formants’). Whereas the
fundamental frequency is determined by the length and
tension of the vocal folds, theory predicts that the
location and spacing of the formants (‘formant
dispersion’) is related to vocal tract length.
Recent studies suggested that formant dispersion but
not fundamental frequency serves as a reliable
predictor of body size and weight. To test this
assumption, we examined grunts recorded from captive
Hamadryas baboons (Papio hamadryas) living at the
German Primate Centre, Göttingen. We used linear
predictive coding to extract the formants, and a
spectrogram-based analysis to measure the fundamental
frequency and a range of other variables related to
the amplitude distribution in the spectrum. Our
results show that – across and within age and
sex classes – the fundamental frequency is more
closely related to most physical measurements
(including vocal tract length) than formant
dispersion. Our findings indicate that depending on
the call type, the fundamental frequency can serve as
a reliable indicator of physical characteristics of
the caller.
Dana Pfefferle
Sounds and size - identification of acoustic
variables that reflect body size in Hamadryas
baboons (Papio hamdryas)
The acoustic structure of
animal sounds may be influenced by a number of
factors, such as the context or the motivational state
of the caller. Due to the mechanisms of sound
production, however, all sounds invariable transmit
information about physical properties of the caller.
In mammals, sound is produced by airflow generated in
the lungs that drives oscillations of the vocal tract
folds located in the larynx. The source signal then
passes the vocal tract, which acts as a
bandpass-filter allowing a narrow range of frequencies
to pass (‘formants’). Whereas the
fundamental frequency is determined by the length and
tension of the vocal folds, theory predicts that the
location and spacing of the formants (‘formant
dispersion’) is related to vocal tract length.
Recent studies suggested that formant dispersion but
not fundamental frequency serves as a reliable
predictor of body size and weight. To test this
assumption, we examined grunts recorded from captive
Hamadryas baboons (Papio hamadryas) living at the
German Primate Centre, Göttingen. We used linear
predictive coding to extract the formants, and a
spectrogram-based analysis to measure the fundamental
frequency and a range of other variables related to
the amplitude distribution in the spectrum. Our
results show that – across and within age and
sex classes – the fundamental frequency is more
closely related to most physical measurements
(including vocal tract length) than formant
dispersion. Our findings indicate that depending on
the call type, the fundamental frequency can serve as
a reliable indicator of physical characteristics of
the caller.
The acoustic structure of
animal sounds may be influenced by a number of
factors, such as the context or the motivational state
of the caller. Due to the mechanisms of sound
production, however, all sounds invariable transmit
information about physical properties of the caller.
In mammals, sound is produced by airflow generated in
the lungs that drives oscillations of the vocal tract
folds located in the larynx. The source signal then
passes the vocal tract, which acts as a
bandpass-filter allowing a narrow range of frequencies
to pass (‘formants’). Whereas the
fundamental frequency is determined by the length and
tension of the vocal folds, theory predicts that the
location and spacing of the formants (‘formant
dispersion’) is related to vocal tract length.
Recent studies suggested that formant dispersion but
not fundamental frequency serves as a reliable
predictor of body size and weight. To test this
assumption, we examined grunts recorded from captive
Hamadryas baboons (Papio hamadryas) living at the
German Primate Centre, Göttingen. We used linear
predictive coding to extract the formants, and a
spectrogram-based analysis to measure the fundamental
frequency and a range of other variables related to
the amplitude distribution in the spectrum. Our
results show that – across and within age and
sex classes – the fundamental frequency is more
closely related to most physical measurements
(including vocal tract length) than formant
dispersion. Our findings indicate that depending on
the call type, the fundamental frequency can serve as
a reliable indicator of physical characteristics of
the caller.