Methods - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 221

Fig. 9.1 Example of sinusoidal curves of different hertz (Hz): 4 and 14 Hz

9.2.1.2 Pitch

Pitch is our subjective interpretation of frequency.

9.2.1.3 Period

Period ( T ) is the time necessary to complete a cycle of a wave for a given point:
T ¼ 1 / f . For example, for f ¼ 550 T ¼ 1/550 s ¼ 1.81 ms (milliseconds).

9.2.1.4 Wavelength

Wavelength ( ) is the spatial period of a sinusoidal wave and is measured in a

homogeneous medium as the distance between two points with the same phase
(crest to crest), or at the intercept with zero: it results from the relationship between
speed and frequency

λ

λ ¼ c / f or λ ¼ cT where c is the speed of the sound and T is the

period (Fig. 9.2 ).

9.2.1.5 Sound Speed

Sound speed ( c ) is the distance that sound covers in a given unit of time. Sound
propagates at different speeds according to the media and is proportional to the
square root of the ratio of the elastic modulus (stiffness) [ k ] of the medium to its
density [

p , which can be calculated as c

K

/T.
The ambient conditions modify sound propagation. In dry (0 % humidity) air at
20 C at sea level, the speed of sound is approximately 343 m/s (1,230 km/h;
767 mph). This number is derived by the formula c air ¼

ρ

]. c

¼ =ρ ¼ λ f or c ¼ λ

(331.3 + 0.606 ϑ ) m/s

is the temperature in degrees Celsius ( C).

where ϑ