*4.3. Workload Assessment*

The Official NASA Task Load Index (TLX) is a subjective workload assessment tool that is used in various human–machine interface systems [58]. By incorporating a multidimensional rating procedure, NASA TLX derives an overall workload score based on a weighted average of ratings on six subscales: Mental Demand, Physical Demand, Temporal Demand, Performance, Effort, and Frustration. The scale from 0 to 10 points is chosen for

the ease and familiarity of participants, with 0 ranging from very low to 10 being very high. TheTLX test was performed using uniform weights for all metrics. The six-color wheel codes achieved 43.75 points, and the eight-color wheel codes achieved 48.75 points.

Figure 7 summarizes workload assessment scores for subjects under the NASA-TLX test. The scores for Mental Demand, Temporal Demand, Overall Performance, and Effort were in the middle or upper-middle. This was because adding three variables to speech sound made it relatively more difficult to use while increasing efficiency. More time needs to be invested in practice and training based on understanding the principles. This also makes the task more demanding for first-time participants and can feel relatively difficult with insufficient learning, which can increase frustration in use. Gradual learning over time makes it less difficult. The reduction in variables and improvements in sound production methods will further reduce the difficulty of use.

**Figure 7.** Workload assessment scores for NASA-TLX test question indicators.

### *4.4. User Experience Test*

User experience (UX) testing of participants in the experiment was performed by modifying the System Usability Scale approach to match the purpose of the experiment. The System Usability Scale (SUS) is a questionnaire that is used to evaluate the usability of products and services. These survey questions are used as a quantitative method to evaluate and gain actionable insights on the usability of a wide variety of new systems which may be either software or hardware [59].

Participants were asked to rate the following seven items:


The UX test scores were broken down for all participants out of 1–5 (strongly disagree through strongly agree). By converting on a hundred-point scale, the six-color wheel code score was 72.32 points, and the eight-color wheel code score was 71.43 points. The scored user experience results are provided in Figure 8. The average Q1 score was 2.5, Q2 was 3, Q3 was 2.63, Q4 was 3.25, Q5 was 3.5, Q6 was 2.75, and Q7 was 2.5. As with the questions discussed in the previous NASA-TLX section, the lack of time and unfamiliarity with the use of the program resulted in relatively low ratings for individual questions.

Table 12 lists the participants' positive and negative feedback.


**Table 12.** Positive and negative user feedback from the UX Test.
