# Interpretability of Methods for Switch Point Detection in Electronic Dance Music
## 2 Related Work
### Datasets  
Prior to this work, there already existed two datasets annotated with cue points: UnmixDB from [26] and 1001 Tracklist from [4]. UnmixDB contains cue points that were generated procedurally, with no particular emphasis on the decision process of real DJs. Instead, the 1001 Tracklist dataset provides an approximate location for cue point(s) in a given track. Specifically, starting from a human-generated DJ mix, every transition from one track to another is annotated with three positions: the point when a new track \"fully appears\" (named \"cue in\"), the point when the current (old) track starts to \"disappear\" (named \"cue out\"), and the \"middle of the transition\" (named \"cue mid\") [4]. Conceptually, the cue mid corresponds to our switch point. However, since the cue mid is obtained by simply dividing evenly the interval between the detected cue in and cue out, it is unlikely that the position thus identified represents correctly a switch point. Moreover, the number of annotations detected for each track depends on both the number of occurrences of that track in the DJ mixes included in the database, and whether or not the procedure to detect cue in and cue out succeeds. Since the dataset contains 13.7 k unique tracks for 20.7 k transitions, the list of switch points per track is not exhaustive.  
In order to develop and test different computational approaches for SPD, we curated a third dataset of 150 tracks--hereafter called EDM-150--by putting the emphasis on the precise and exhaustive annotation of switch points for each track. To this end, we asked five experts to independently annotate a subset of the tracks by identifying all the switch points therein. Since the concept of switch point is not universal, we provided the annotators with a description of a switch point and three rules, inferred from common DJ practices, to be followed as guidelines:  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Work** & **Features** & **Decision Rules** \\ \hline
[15] & MFCC with CK & PP and period quantization \\
[17] & (Semitone) PCP with CK & PP and period quantization \\
[18] & (Harmonic) PCP with SF & PP \\
[5] & CQT and MFCC & SC \\
[16] & MFCC and energy with CK & PP and period quantization \\
[19] & Timbre and PCP with fusion (CK and SF) & PP and loudness and position \\ \hline \hline \end{tabular}
\end{table}
Table 1: Overview of works related to the selection of switch points.  
A switch point is always located on the downbeat at the start of a period.
2. A switch point marks a position of high novelty in features such as rhythmic density, loudness, instrumental layers, and/or harmony.
3. Switch points are located in the initial portion of the track that precedes the first point of salience.  
Even with these rules in place, though, the annotations returned by the experts varied greatly, confirming the subjective nature of switch points. We handled this issue by merging the annotations by taking the union of all the annotations from the different experts. This operation effectively increases the exhaustiveness of the annotations and reduces the likelihood that a position (as returned by an algorithm) is mistakenly reported as an error despite being a viable switch point (\"false negative\").  
In summary, EDM-150 consists of 150 tracks of EDM, selected from a period of 30 years (1987-2016), a variety of musical subgenres, and a tempo ranging from 99 bpm to 148 bpm. The average duration is 7 min 20 s per track, for a combined duration of 18 h 20 min. Each track was independently annotated by exactly three experts who identified 625 unique positions with a minimum of 1, a maximum of 9, and a mean of 4.2 positions per track. Most positions were identified by two or three annotators (184 by two, and 185 by three) and 256 by only one. As a final stage in the curation of the dataset, the experts verified that those positions identified by only one annotator do in fact comply with the three aforementioned rules.