Psychoacoustics

 

We've been mulling - as you do at our age; actually mulling is practically a full-time activity at the moment - on our collective hearing loss for whatever reason; mostly age, viral infections and too much loud music in our prime, etc. Two things afflict our hearing at the moment: a severe suppression of the narrow speech band, between approximately 300Hz and 3,000Hz, and anomalies in perception of audio directionality - some sounds can't be located spatially as before.

As one would expect, we have a tailing-off of frequencies above 10 kHz, quite normal in and of itself with ageing, but the drop in sensitivity to the speech band is weird - in my case particularly because my perception of frequencies between 3 kHz and my current ceiling of around 9.5-10 kHz-ish is OK, somewhat annoying as vocal sibilance is within that gamut; so whilst a lot of speech sounds muted, some voices have a pronounced edge which grates rather.

This has reminded me of times past in the audio-visual business, back in the days when I still had decent hearing. Joe & I were working on the first big contract we did: the AV displays for Thorn-EMI: principally the interactive lobby displays at their West End corporate headquarters and the big EMI showcase at their Central Research Laboratories in Hayes, Middlesex [sadly, no longer there], featuring amongst the exhibits equipment from Abbey Road and the Beatles' time there.

Some time after we had completed the contract, Joe & I went down to CRL to meet a contact there, and we were given a demo of some  new stuff they were playing with at the time, which aimed to recreate a true three-dimensional sound field using a normal stereo source and delivery system. The nascent technology was dubbed 'Sensaura' and was a Thorn-EMI in-house project at the time. The demonstrations were impressive: either played through stereo speakers, or through headphones. I think the latter example was particularly staggering: offering total immersion in a 3D sound field through two closed audio sources directly coupled to the ears: no reflected sound tricks or chicanery involved.

They played us a variety of field recordings, and in all cases sounds moved around the head, over the head, occupied genuine spatial locations hard left and right [as opposed to panned hard left or right - effectively mono], just as in the real world. I still have a demonstration CD we were given on the day somewhere in my collection: I must dig it out sometime and revisit it. On asking how the bloody hell it worked, we were told it was all down to psychoacoustics and human evolution.

The human brain is almost hard-wired to perceive certain frequencies or groups of frequencies as coming from a certain direction: a defence mechanism against the myriad predatory threats that would have presented themselves to our ancestors: some sounds always appear to come from above, even to young, healthy ears/brains, for instance. By subtly manipulating certain frequencies in a binaural recording, using comb filters and post-processing techniques of a then arcane nature, the boffins at CRL could fool the brain into perceiving sound as coming from any direction they chose.

These days, the fruit of this research is part and parcel of daily life: a fairly cheap TV soundbar can fool you into believing sounds are arriving at your ears from at least either side of you, or in the best cases from right behind you. Remarkable stuff, if your soundbar hasn't died like ours recently did! It was a great privilege to be given private insight into an emerging technology in its very earliest days, and the knowledge I gained from it goes some way in explaining some of our current, personal aural issues!