## 5 Varying Noise Level--Word Frequency Results
Observe that about half of this command word fails at 70 dB, which is poor for a key command word for which a higher resilience is needed at higher levels of 75 dB and perhaps 80 dB. Figure 9e,f shows the frequency map and trendline of the third speech word (SW3), 'Backward', which appeared only two times in the 12 speech command set. It had a better performance than SW2, notably at both 75 dB and 80 dB. Figure 9g,h shows the frequency map and trendline of the fourth speech word (SW4), 'Right', which also appeared only two times in the 12 speech command set, was the most noise resilient and hence the most successful speech command word with a high recognition accuracy of about 90% at 80 dB. Figure 9: Speech word (SW) frequency map and trendlines I. (**a**) SW1 frequency map, (**b**) SW1 trendline, (**c**) SW2 frequency map, (**d**) SW2 trendline, (**e**) SW3 frequency map, (**f**) SW3 trendline, (**g**) SW4 frequency map, (**h**) SW4 trendline. Figure 10: SW frequency map and trendlines II. **(a)** SW5 frequency map, **(b)** SW5 trendline, **(c)** SW6 frequency map, **(d)** SW6 trendline, **(e)** SW7 frequency map, **(f)** SW7 trendline, **(g)** SW8 frequency map, **(h)** SW8 trendline. Figure 11: SW frequency map and trendlines III. (**a**) SW9 frequency map, (**b**) SW9 trendline, (**c**) SW10 frequency map, (**d**) SW10 trendline, (**e**) SW11 frequency map, (**f**) SW11 trendline, (**g**) SW12 frequency map, (**h**) SW12 trendline. Figure 10 shows the results of four speech words, SW5-SW8. Figure 10a,b shows the frequency map and trendline of the fifth speech word (SW5), 'Left', which appears twice in the 12 speech command set. Figure 10c,d shows the frequency map and trendline for the sixth speech word (SW6), 'Step', which appears four times in the 12 speech command set. Figure 10e,f shows the frequency map and trendline for the seventh speech word (SW7), 'Hover', which appears twice in the 12 speech command set. This was the least successfully recognised speech command word across all participants, with a recognition rate of 36 % at 65 dB. Figure 10g,h shows the frequency map and trendline for the eighth speech word (SW8), 'Land', which appeared only once in the 12 speech command set. Note that this has exactly the same frequency map and trendline characteristic as speech command SC6 'Land' in Figure 5a,b because it is a single word command that appears only once in the speech command set, therefore both speech command and individual word dimensions of analysis yield the same result. Figure 11 shows the results of the remaining four speech words, SW9-SW12. Figure 11a,b shows the frequency map and trendline of the ninth speech word (SW9), 'Half', which appears twice in the 12 speech command set. Figure 11c,d shows the frequency map and trendline for the tenth speech word (SW10), 'One', which appears three times in the 12 speech command set. Figure 11e,f shows the frequency map and trendline for the eleventh speech word (SW11), 'Metre', which appears five times in the 12 speech command set. This had the highest frequency of occurrence because it is a modifier specifying the unit of movement in any direction being given by the keyword. Figure 11g,h shows the frequency map and trendline for the twelfth speech word (SW12), 'Stop', which appeared only once in the 12 speech command set. This has exactly the same frequency map and trendline characteristic as speech command SC12 'Stop' in Figure 6e,f because it is a single word command that appears only once in the speech command set; therefore, both speech command and individual word dimensions of analysis yield the same result.