## 3 Materials
### Audio and Transcriptions Files
Since recordings are scheduled in advance, the scheduled starting time is usually some minutes before the lecture actually begins, and the end of the class may also be a few minutes before the scheduled ending time. Consequently, the recordings contain several minutes where the microphone is off, leaving the recording with muted segments that we defined as Miscellaneous. We defined as a Pause a segment of audio where the lecturer does not speak for more than 2 s. However, during this period of silence, students chat among themselves and, sometimes, they speak loud enough to be captured by the lapel microphone worn by the lecturer. We defined this occurrence as Indistinct Chat. As can be observed in Figure 2, Indistinct Chat is clearly distinguishable from segments where the lecturer speaks, as it happens in Figure 3, in which the teacher makes a digression commenting on some question of a test (see transcription in Table 2), and in Figure 4, in which the words of the teacher are concerned with the organization of the class, particularly, the teacher is announcing a five-minute break (see transcription in Table 3). One can notice the distinction between Indistinct Chat and Digression or Organization by comparing the difference in the amplitude of the corresponding waveforms. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Course Name** & **Male** & **Female** \\ \hline Electronic devices & - & 330 min \\ Digital signal processing & - & 360 min \\ Mathematics & 330 min & 344 min \\ Measurement systems & - & 120 \\ Microprocessed systems & 360 min & - \\ Networks and teledetection & 564 min & - \\ Oceanographic physics & 600 min & - \\ Physics & 90 min & - \\ Statistics & 225 min & 450 min \\ \hline Total & 2169 min & 1604 min \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Breakdown of the dataset by minutes per course and per gender. Context: The lecturer makes a comment about a detail of a test  
Some of you have told me that I had, I put a minus on the test because I got a minus. It can't generate power, OK? It has to dissipate power. In the tables, it will always come up as dissipated power. Right? If you get a minus, you got one of the minus signs wrong. OK? Interaction: In Figure 5, and its corresponding transcription in Table 4, we can observe that this audio sample interleaves segments of short silences with segments of the teacher's speech, usually indicating that the lecturer is conversing with a student. \begin{table}
\begin{tabular}{l} \hline Context: The lecturer makes a comment about a detail of a test \\ \hline Some of you have told me that I had, I put a minus on the test because I got a minus. It can’t generate power, OK? It has to dissipate power. In the tables, it will always come up as dissipated power. Right? If you get a minus, you got one of the minus signs wrong. OK? \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Transcription of Figure 3.  
Figure 4: Audio sample of an Organization segment. Figure 3: Audio sample of a Digression segment. Figure 2: Audio sample of a Miscellaneous segment followed by Indistinct Chat. Exercise: Figure 6 and its corresponding transcription in Table 5 shows an audio sample that also interleaves periods of silence with teacher's speech, like in Interaction, but in this case the duration of the segments of speech and silence are generally longer than in Interaction. The silences in Figure 6 mainly happen when the teacher is writing on the blackboard and stops sporadically in order to check if students are able to follow the explanation. Looking at the content of Table 5, we can conclude that the lecturer is solving an Exercise due to the use of variables and formulae and the fact that an equation for a specific electric circuit is being solved. Theory/Example/Organization/Digression/Other: We grouped all these labels together because clearly and distinguishable audio features that discriminated among the teaching activities did not exist, as all of them were consistent with the audio signal of a