Outdoor Acoustic Propogation

Dear Colleagues,

Many speech researchers, such as phoneticians, phoniatrists, speech technologists, etc., are used to high-quality recordings in specially built recording studios, e.g., anechoic chambers, where reverbations (sound bouncing off walls or other items) are brought to a minimum. Many studies devoted to the singing voice have been performed under such “ideal” circumstances, and detailed studies of the singing voice, both in terms of its acoustics and underlying physiological basis (e.g., using MRI or high-speed photography), serve the purpose of relating the singing voice to its intended arena, e.g., concerts halls (for classical singing), adapation to microphones (popular/rock singing) or outdoor settings, for singing modes such as yodelling, cattle calls (many parts of the world, e.g., kulning in Sweden).

Previous studies have shown that acoustics differ between singing styles intended for indoor and outdoor setting—kulning exhibits clear and visible harmonics at far higher frequencies than classical head voice singing, for example. It has also been shown that physiological production mechanisms differ between different modes of singing, likely created in order to obtain and create sounds that can be carried far in a habitat with specific and special sound propagation characteritics, such as foliage, tree trunks, various types of ground, as well as other outdoor phenomena (lacking in indoor settings), such as wind shear, humidity, low/high clouds, and so on. As an aside, the same problems pose a problem to the exploding field of animal vocalizations research, where most of the data collection is not only carried out on “unwilling” subjects but also very often occurs in natural settings, where there is a lot of background noices that contaminate the signal which is the focus of the study.

The conclusion to draw here is that while it is fairly easy to record data with high ecological validity—just put the singer/animal in their natural, outdoor setting and start recording—the acoustic characteristics of any outdoor setting present many problems to the researcher that need to be considered. Other factors that need to be considered include the height from the ground of the sound source, which differs between, e.g., Swedish cattle calls, kulning, produced at around 150 cm above the ground and carrying more than 2 kilometers, and lion roars, produced at around 80 cm above the ground, but which can carry up to 8 kilometers in the habitat where they are produced.

This Special Issue of Applied Science invites researchers to submit papers that focus on but are not limited to the following topics:

–   Outdoor recordings in different habitats;

–   Studies of singing techniques, in indoor and outdoor settings;

–   Comparison of singing techniques, acoustically;

–   Studies of, and comparisons between, the physiological production mechanisms in different singing styles, with different intended setting (concert halls, forested outdoor areas, etc.);

–   Studies of animal vocalizations in different habitats, e.g., high up in trees (monkeys), on the ground (lions, savannah mammals and many more).

Dr. Robert Eklund
Guest Editor

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• Sound propagation
• Attenuation
• Propagation
• Reverbations
• Echo location
• Wind shear
• Acoustic analysis*
• Phonetic analysis (vowels, tones/notes)
• Technical recording equipment (microphones, parabols, sonars)
• Acoustic analysis software
• Physiological studies of voice (MRI, EGG, high-speed photography)
• Singing styles