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.