Even using the latest technology surround sound system, hearing aid users are subjected to propagation delays and distortion. The sound from each channel arrives at their hearing aid microphone and the hearing aid amplifier reacts poorly to differences in the timing and amplitude.
Figure 1: Normal (unprocessed Audio Signal) Plenty of difference between soft and loud - Normal Dynamic Range
Figure 2: Audio after compansion/re-emphasis Reduced difference between soft and loud - Reduced Dynamic Range
Figure 3: Result after additional processing by a hearing aid Further reduction in the difference between soft and loud combined with significant loss of information
Figure 4: The missing information!
Figure 1 shows the normal audio waveform before any signal processing during production is introduced. Figure 2 shows the changes made during production with softer sounds made louder (this is what we normally hear from the TV). Figure 3 shows the changes made by the hearing aid as it compresses the artificially loud signal and reduces the dynamic range even further. Figure 4 shows the vital information that has been removed from the original sound.