So we discovered a special quality about audio doses yesterday, and how the dose is eliminated after you stop listening to the noise. And we know already that if a person is exposed to loud noise, people with normal hearing will exhibit an ephemeral threshold elevation. On moving back into a quiet listening environment during the conversation, their hearing will shift back to normal.
I already have two USPTO Patents based on taking advantage of that effect to help people listen to telephone conversations in the presence of loud noise, without using noise cancellation, nor blocking their ears from the sound environment. (USPTO 8,964,998 and 8,913,754).
So, what is this thing we refer to as a maximum daily dose? We have research that shows that listening beyond this maximum daily dose invites permanent hearing damage. And that is the same as stating that you will have a permanent threshold elevation shift, even in quiet conditions.
So it seems that audio dose is related to a quiescent threshold shift. My own patents presumed that over the course of a phone conversation your threshold would temporarily shift upward, then restore almost immediately. But phone conversations are typically only a few minutes long, and I wasn’t addressing situations with damaging noise levels. The dosing profile covers 8 hours of exposure before you reach damaging accumulation at mild exposure, sooner if the noise is really loud.
In other words, the dose relates to how long it takes your induced quiescent threshold elevation to recover back to its normal levels, and how much that quiescent shift is. And the dosing profile would suggest that the quiescent shift rises to match the sound field level after 8 hours of continuous exposure, only to recover after 10 hours of quietude.
The evidence suggests that the baseline quiescent level shift, even with damaging exposure is initially slight. But continued damaging exposure shifts that baseline higher and higher over time.
But ephemeral shift will affect your listening in the moment, immediately after prolonged exposure. I think that being exposed to 8 hours of continuous noise at 85 dBSPL, means that your threshold elevation matches that 85 dB and only gradually recovers back to its normal level, following the relaxation profile.
So you will need a Crescendo to hear that music clearly, after such prolonged exposure – even if you have normal hearing. And in fact, Crescendo could be made better by helping you with some knowledge of your recovery profile. This is an extension of my two Patents – an adaptive Crescendo, if you like.
And this also means that if you allow yourself to accumulate a significant fraction of a daily dose, during your listening sessions, that your threshold will gradually shift higher and higher – leading to a loss of clarity in your musical listening. Ear Fatigue…
And the dosing profile also suggests that if you listen to loud for much longer than a couple of hours, you will have lost enough clarity that you should go do something else for a couple of hours and come back.
This may also explain why people with normal hearing actually like Crescendo. Immersed in our daily existence, the ear is exposed to continuous noise levels for hours on end. If you play mostly in a relatively quiet room, then you should see an ephemeral shift to the 40-50 dB level. And you would benefit in the moment from a Crescendo tuned somewhere around that level, even though you have “normal” hearing.
Interesting, how our hearing actually works…