## 6 Evaluation
### Evaluating the Usability of Chordais-Gen as an Assistive Tool  
In this third experiment, we aimed to evaluate the usability of ChordAIS-Gen from a user perspective. The system presented aims to help those users who might not have enough knowledge about tonal music to generate a good chord progression. The algorithm facilitates generating different but good options for candidate chords which can follow the progression, but we also want to validate if these chords are suitable selections for the user. In total, 8 users without musical training were selected and asked about their experience with ChordAIS-Gen. Initially, they used the system to generate 5 chord progressions with any degree of freedom, to become familiar with ChordAIS-Gen. Then, they had to generate a total of 10 progressions. Each chord progression consists of a minimum of 5 chords and a maximum of 16 chords in a concrete key signature and with different curves. Initially, the users select the key, the number of chords and the tension profile. Then, ChordAIS-Gen proposes three-chord progressions. The user can play the progressions whenever they need to and select which one is more desirable according to their criterion. They can modify a concrete chord if they wish to. The interface constructed is shown in Figure 7.  
To also compare the ChordAIS-Gen system with our previous work, ChordAIS, we repeated the experiment with the same users. They used the ChordAIS system to generate 10 chord progressions, in the same conditions as in ChordAIS-Gen. In every case, the chord progressions that both systems proposed are not ordered by their fitness, in order not to bias the selection of one particular progression. All the participants have used the tool for at least 10 min, and have generated a minimum of 8 progressions. With that experience, they had to respond to a questionnaire that aims to capture their opinion about the system. In particular, the users gave their opinion about three items:  
* The system complies with their expectation. The system is capable of giving good solutions that follow the initial parameters (tonal tension, key and number of chords). Figure 7: Interface of ChordAIS-gen.  
* The system can give nice chord progressions that the user could not otherwise have composed. * The system presents solutions that are different among them. All the questions could be rated from \(1\) (\"Completely unsatisfied\") to \(5\) (\"Completely satisfied\"). Table 3 shows the mean ratings and the standard deviation of the experiment. The table shows that, in general, ChordAIS-Gen satisfies users' requirements (4.29). The users are satisfied with the system, as it is capable of retrieving good and different candidate progressions that adapt to the tonal tension profile, with a mean of 4.45. Additionally, the users consider that amount of options to select chord progressions to be quite adequate (4.34), meaning that ChordAIS-Gen can retrieve solutions which are different one from another. The authors consider that this feature can be improved in future work by adding a learning component to understand the users' preferences and incorporate this to the selection of chord progressions. The previous version, ChordAIS also obtained good results. The satisfaction degree and the usefulness of the ChordAIS also had high ratings, although slightly lower than in the new version. However, ChordAIS cannot retrieve information about the tonal tension profile, only about the key and number of chords. Additionally, the users gave a lower value when they were asked about the diversity of solutions (3.17). Thus, the users think that both systems can assist them but ChordAIS generates more expected chord progressions than ChordAIS-Gen. It is important to note that we also gave space to make some qualitative comments about our application and the experiments with the curves. Regarding the interface of our system, musicians would prefer to show the progressions with a musical score instead of a MIDI list.