Table 2.
Spectro-temporal measurements taken from complete duets, overlapping duet sections, overlapping syllable parts, and non-overlapping syllable parts
| Acoustic measurements | Code | Description |
|---|---|---|
| Duration (s) | DUR | Signal length |
| Mean frequency (kHz) | AVF | Weighted average of the frequency spectrum based on the amplitudes within a specific frequency range (0.5–22.05 kHz) |
| Standard deviation of frequency (kHz) | STF | Standard deviation of the frequency spectrum, with each frequency component weighted according to its amplitude within a specific frequency range |
| Median frequency (kHz) | MEF | Frequency at which the frequency spectrum is split into 2 equal-energy frequency intervals |
| Frequency Q25% (kHz) | F25 | Frequency where the frequency spectrum is divided into 2 intervals with 25% and 75% of the energy, respectively |
| Frequency Q75% (kHz) | F75 | Frequency where the frequency spectrum is divided into 2 intervals with 75% and 25% of the energy, respectively |
| Interquartile frequency range (kHz) | IFR | Frequency interval between Frequency Q25% and Frequency Q75% |
| Median time (s) | MET | Time point at which the time envelope is split into 2 equal-energy time intervals |
| Time Q25% (s) | T25 | Time where the time envelope divided into 2 intervals with 25% and 75% of the energy, respectively |
| Time Q75% (s) | T75 | Time where the time envelope divided into 2 intervals with 75% and 25% of the energy, respectively |
| Interquartile time range (s) | ITR | Time interval between Time Q25% and Time Q75% |
| Skewness | SKW | Frequency spectrum asymmetry indicates whether the spectrum is skewed to left (S < 0) or right (S > 0) |
| Kurtosis | KUT | Peakedness of the frequency spectrum indicate how much the spectrum deviates from a normal shape (K = 3) |
| Spectral entropy | SEM | Distribution of energy in the frequency spectrum from pure tone (0) to noisy (1) |
| Time entropy | TEM | Distribution of energy in the time envelope from amplitude concentrated in a specific point (0) or spread throughout the recording (1) |
| Spectrographic entropy | SPE | Product of spectral entropy and time entropy from pure tone (0) to noisy (1) (no unit) |
| Spectral flatness | SPF | Similar to spectral entropy from pure tone (0) to noisy (1) (no unit) |
| Mean dominant frequency (kHz) | AVD | Mean of dominant frequency measured across time points in the spectrogram |
| Minimum dominant frequency (kHz) | MID | Minimum of dominant frequency measured across time points in the spectrogram |
| Maximum dominant frequency (kHz) | MAD | Maximum of dominant frequency measured across time points in the spectrogram |
| Dominant frequency range (kHz) | DFR | Range of dominant frequency measured across time points in the spectrogram |
| Modulation index | MOD | Cumulative (absolute) variations between consecutive measurements of dominant frequency divided by dominant frequency range |
| Start dominant frequency (kHz) | SDF | Frequency at the start of the signal |
| End dominant frequency (kHz) | EDF | Frequency at the end of the signal |
| Dominant frequency slope (kHz/s) | DFS | Change in dominant frequency expressed as ((End dominant frequency—Start dominant frequency)/Duration) |
| Mean peak frequency (kHz) | MPF | Highest-energy frequency within the mean frequency spectrum of a time wave, where the mean frequency spectrum represents the mean relative amplitude of the frequency distribution |
Spectro-temporal measurements were extracted from acoustic signals using the spectro_analysis function from warbleR package in R (Araya-Salas and Smith-Vidaurre 2017).