## 4 Varying Noise Level--Speech Command Results  
The varying noise level speech command results from the experiment are recorded in a spreadsheet document, which is made available as downloadable supplementary material/dataset for this research paper. The blanks indicated by an underscore, in the varying noise level speech command result spreadsheet tab, are points were the data was not available due to lab threshold noise levels being higher than specified, caused by uncontrollable ambient noise conditions during experiments. In addition, all of participant A1's data in this segment were corrupt due to setup failure at the beginning of the experiments. The implication of this is that the total sum of utterances may be fewer than 37, mostly 36 at each noise dB level. Each of the 12 speech commands were collated across the 37 participants, and the number of words successfully recognised were plotted against the noise levels with the number of times the number of words were recognised for the particular speech command by different participants, which is the hit frequency of each point on the plot was being indicated in brackets. This was called the frequency map. A MATLAB program was written to collate and plot the data from the result table. From the frequency map shown in Figure 2, it can be observed for the two-word speech command \"Go Forward\" that all of the 23 utterances successfully made at 55 dB were successfully recognised as two-word commands, as indicated in the bracket next to the point on the frequency map plot. In addition, at 60 dB, it can be observed that, of the 35 successfully registered commands, 30 were two-word (full recognition--success), four were one-word (partial recognition--partial success), and one was no-word (recognition failure). The distribution of the partial success is presented in the next section on \"variable noise level--word frequency.\" At 65 dB, there were 36 commands that were successfully registered/uttered/recorded, but only 27 were two-worded (success), five one-worded (partial success), and four failures (no-word). At 70 dB, 11 were successfully recognised as two-worded, 12 partial success (one-word), and 13 failures (no-word). At 75 dB, there were 36 registered commands, eight two-word success, seven one-word partial success, and 21 failures (no word recognised). At 80 dB, there were 36 registered commands, zero two-word success, six one-word success, and 30 failures (no-word). At 85 dB, 36 registered commands, and 36 failures, no word was recognised at 85 dB by the custom UAV-Speech interface. A trend can be observed here, that at the lower dB noise level, the two-word speech command \"Go Forward\" was successfully recognised, whereas recognition fails at higher dB noise levels. This trend is graphically shown by the trendline plot in Figure 3. The points on the trendline were computed by taking the vertical weighted average from the frequency map as follows:  
\[y(x)=\frac{\sum_{i=0}^{n}d_{i}(x)f_{i}(x)}{\sum_{i=0}^{n}f_{i}(x)}, \tag{1}\]  
where \(n=4\) is the maximum number of speech command words used in the experiment. \(d_{i}(x)\) is the specific number of speech command words being registered, for the given \(x\) dB noise level. Note that this corresponds to the \(i\)th value. \(f_{i}(x)\) is the frequency of the \(d_{i}(x)\) point, as indicated on the frequency map, for the given \(x\) dB noise level. For example, the points on the trendline for the first speech command (SC1), \"Go Forward\" was computed as follows:  
When \(x=55\) dB  
\[y(55)=\frac{\sum_{i=0}^{4}d_{i}(55)f_{i}(55)}{\sum_{i=0}^{n}f_{i}(55)}. \tag{2}\]  
Figure 3: SC1 trendline. Figure 2: The first speech command (SC1) frequency map.