There are two types of acoustic unit in
Luscinia:
Elements are the smallest acoustic unit; they are
defined as a temporally continuous region of sound. At each
time slice, an element may contain more than one region in
the frequency domain (for example, in a harmonic signal).
On the other hand, it is possible that two elements might
overlap in time. In practice, what this means is that an
element is recorded by Luscinia as an area within the
spectrogram: for each time slice, Luscinia records the
time, and the minimum and maximum frequencies of each
frequency band that is considered part of the signal. When
you measure an element in Luscinia, the element is
indicated as a green region that overlies the spectrograph.
The shape of that green region accurately represents what
Luscinia has recorded about the location of the element.
Elements are also identified by numbers placed just above
the top of the spectrograph.
Syllables are sequences of elements. Many
animal signals (especially bird songs) contain
hierarchically structured sequences of elements, and
syllables are a way of capturing that organization. A
syllable is simply defined by its start and end time:
Luscinia searches for all elements that fall within that
region in time. Luscinia also recognizes hierarchies within
syllables: for example chaffinches (Fringilla
coelebs) sings songs in which a few elements are
organized into syllables. Each syllable is then repeated a
number of times, before the bird switches to a different
syllable. In this case, each syllable is measured, and then
one syllable is used to record the repeated sequence of the
same syllable. This higher-order syllable is automatically
recognized by Luscinia as being such, and it is displayed
differently accordingly. A measured syllable is identified
by a red bar across the top of the spectrograph (just above
where the elements are listed), with a number inside it.