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Context: The proposed architecture of VTHarm is inspired by [22]. VTHarm has an additional probabilistic encoder for a latent variable z , where z represents the global attribute of the aggregated melody and chords. We denote this encoder as the context encoder . We add a global key signature label as a conditional input token to the model. The key signature is essential for an arbitrary melody to obtain a certain harmonic context [41]. The key signature token can aid the model in specifying the latent space and sampling the outputs from the human-composed samples from CMD and HLSD include 72 different chord types with various amounts of musical tensions. 2) STHarm may generate common chords more fre- quently from the average chord distribution than the human- composed music, as shown in the lower diversity scores. Concretely, the most frequent chords in real-world music are diatonic chords such as the C, G, and F major chords in the C major key [9]. Since these chords have relatively less musical tension with respect to a melody, they are close to the melody under a music-theoretical space. Thus, these chords may obtain better coherence scores than other chords with more musical tension. Moreover, Human shows lower diversity scores than the variational models. We assume that this is because these mod- els can produce some infrequent chords far from the mean distribution of real-world music. The nature of stochastic generation models draws samples from the normal distribu- tion [49]. Some of the generated chords may violate the given key signature but increase the information outside the certain harmonic context. Hence, they may contribute to higher chord diversity than human-composed music. We conduct an ablation study to verify the beneﬁt of adding the conditional token c to VTHarm and rVTHarm. We assume that c provides key signature information that can efﬁciently constrain the latent space to a concrete harmonic context, improving the chord structuredness and reconstruction per- formance of the model. We compute the chord similarity metrics between the ground truth and generated chords from the VT models according to the presence of c . The results are demonstrated in Table 7. This table shows that the VT models without c mostly obtain worse scores for all similarity metrics than the models with c . This indicates that adding key signature information to the VT models in most cases not only enhances the one-by-one accuracy but also improves the structure of the generated chords to be more human-like.

Question: What does "global key signature" mean?
"Global key signature" means the harmonic context of music that is constrained to a certain range. For example, the C major key is constrained to have functionally important chords such as C, G, and F major chords.