Methods - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 233

Fig. 9.10 A spectrogram represents the distribution of frequencies with time and according to the
value of amplitude ( in colors )
spectrogram with a finer time analysis resolution but correspondingly a coarse
frequency resolution (Fig. 9.9 ). Generally the selection of a record of 512 points
is a reasonable compromise to have a satisfactory resolution in time and frequency,
but the choice of resolution depends on the goal of the spectral analysis (Fig. 9.10 ).
Otherwise it is possible to process two spectrograms, one at high-frequency
resolution and the second at high time resolution. Several types of software offer
a spectrographic analysis with different graphical resolution and editing routines
and the possibility to banding the sound data into equally spaced fractional octave
bands (1-, 1/3-, 1/12-, 1/24-).
9.6 Field Recording Procedures
Today technological improvements in the field of digital sound offer a great
potentiality in term of recording apparatus. After the period of magnetic tape
recording now we are in the era of digital recording (Rumsey and McCormick
2009 ). The broad variety of commercial digital devices available is sufficient to
guarantee the quality of the recordings (Mennill and Fristrup 2012 ), as is especially
true for the airborne sound microphones that for a modest price can guarantee the
same accuracy with frequency when compared with more expensive devices.
The collection of sound from an aquatic medium remains expensive. For this
application are required hydrophones at high sensitivity and special apparatus to
place such instruments at different depths in bodies of water. Similarly, the devices
required to collect information from soil where geophones and piezoelectric sensors
coupled with signal amplifiers and filters are required appear quite sophisticated.
Recording in the field can be done using a single microphone (mono/stereo), a
set of coupled oriented microphones (mono/stereo), or an array of microphones
(mono/stereo) Fig. 9.11 .