Star Wars and a return to the low-frequency side of the Force- part 1

I just saw Star Wars and I will not give you my opinion of it, nor let the cat out of the bag about any plot details but it seems that this third generation of Star Wars now uses an 80 Hz rumble whenever the force is used.

It’s always amazing how non-speech and non-music sound effects, or FX, can add so much to a movie. However, even without the 80 Hz reminder of the force, I could easily deduce when the force was being used – we could all feel our throats being crushed – but it was still nice to have an added sound effect that wasn’t really noticeable at the time. The 80 Hz comment actually came from my son after the movie was over but as soon as he said it, I immediately realized that he was spot on.  Wouldn’t it be nice to have sound effects to help with speech intelligibility?  Imagine an 80 Hz rumble whenever there was a very high frequency sibilant such as an /s/ which may not be audible to a hard of hearing listener.

This is not a new idea and Harry Levitt wrote about this in the 1980s when he was at CUNY in New York City.  Specifically Dr. Levitt wrote about “surrogates” for inaudible speech.  Actually  Dr. Levitt ran across this idea much earlier in his career.  When he was at Bell Labs, a colleague of his, Newman Guttman, alerted him to the ideas of Bertil Johansson who in the 1950s and 1960s conceived and developed the idea of using a low frequency cue for a potentially inaudible high frequency sound.

Imagine someone with a high frequency hearing loss having some difficulty hearing on the phone – in this surrogate system an /s/ would be detected and either enhanced or be replaced by a more audible sound.  The surrogate may be at the same frequency but perhaps at a higher sound level, perhaps transposed to a lower frequency with better audibility, or perhaps even inserted as a well-defined cue to the audible signal such as an 80 Hz buzz or rumble. Actually on the phone it would have to be around 350 Hz or 400 Hz since phones only transduce down to about 340 Hz. But on the television or radio it could be down around 80 Hz and although the average person may not be consciously aware of it, a hard of hearing person with some auditory training, or perhaps even just being made aware of its existence, may be able to derive some benefit from it.

Surrogates for speech that is otherwise inaudible is not a new concept but it’s nice to be reminded of 40 or 50 year old research that would have been difficult at the time, but may be significantly easier to implement today with current digital signal processing strategies or algorithms.

Electrical engineers and signal processing software engineers are fond of saying that anything can be done in the digital domain; the issue is of what exactly needs to be done for the improvement of speech intelligibility and music enjoyment. Perhaps the missing algorithms and strategies are from Harry Levitt’s surrogate work of the 1970s and 1980s?

An inherent problem with many FX sound effects we see is that they are below the typical speech range of hearing- audible but not speech-like. If one has normal, or near normal low frequency hearing, the force cues in Star Wars are quite audible and add significantly to the overall movie going experience.  But people with a significant reduction in low frequency hearing sensitivity may have to rely on the visual and contextual cues only.

One strategy is to have the hard of hearing person remove their hearing aids during shows like Star Wars, or perhaps ask them to use a different earmold with significant venting during these shows. While it may not be optimal for conversational speech at 65 dBA, movies tend to be 80-90 dBA so these alternative earmold strategies may be quite useful.

In part 2 of this blog series, the effects of super low frequency cues that are infra-sound will be discussed. Did you know that exposure to 10-18 Hz will make you pee?