Privacy Threats of Acoustic Covert Communication among Smart Mobile Devices

Figure 12

Functional test of security model based on high-frequency filtering.

(a) Time Domain of Normal Audio

(b) Time Domain of Synthetic Audio

(c) Time Domain of Filtered Audio

(d) Frequency Domain of Normal Audio

(e) Frequency Domain of Synthetic Audio

(f) Frequency Domain of Filtered Audio

(g) Frequency Spectrum of Normal Audio

(h) Frequency Spectrum of Synthetic Audio

(i) Frequency Spectrum of Filtered Audio