It’s a condition that not everyone with hearing impairment may have. But if you have it, here’s how you can tell…
Hyper-recruitment is the condition that, in some frequency zones, sounds grow more loudly too quickly, as they exceed your elevated threshold at those frequencies. And it can often become unpleasantly loud in those frequency zones.
But you probably won’t notice it until you begin correcting your hearing with something like Crescendo. Then, some forms of music will begin to elicit what may sound like a sympathetic vibration of a loose screw or joint in your headphones or speaker. It sounds very much like a vibration of a loose assembly in a car at highway speed. Sort of a faint buzzing sound.
And at first, you may find yourself looking for what could be the source of that faint vibration. You try a different set of headphones, just in case you somehow damaged the ones you had been using, after you dropped them on the floor a while ago.
But the vibration persists. You even try reversing the left/right orientation of your headphones on your head, if it seems to be coming mostly from one side. But the sound is still there, on the same side, in the background.
Mine gets tickled by high string sections, or female voices that are layered thickly with lots of lush reverb to smear them together.
Finally, you realize it must be in your hearing. Mine is on the left side mostly.
So now, it is time to pull up an EQ ahead of Crescendo, with a bell-shaped boost of 6-10 dB. Make it narrow but not too narrow, and sweep up and down in frequency until you notice that vibration sound growing much more prominent.
At that point you have found the frequency zone. Now invert that boost to become a gentle dip at that frequency, and try nudging the cut deeper, little by little, until you notice that vibration sound disappearing.
At that point you have localized the hyper-recruitment, and neutralized it with an EQ cut just ahead of the Crescendo corrections. That’s exactly how you correct for it. Cutting a dip in the spectrum fools Crescendo into applying a steeper amount of correction against a softer level of sound. And the combination of less loudness with more correction is just right for knocking down hyper-recruitment.
It is completely trial and error. There are no diagnostic tests for it. And you may find yourself repeating the test if you didn’t quite get it knocked down the first time. You can also try broadening the dip, or narrowing it. When you narrow, use more dB for a deeper cut. When you broaden the dip, make the cut less deep. Make it just wide enough, and deep enough, to relieve the problem.
I just did mine again today, for the millionth time. And I ended up doing about half the correction with a broader dip of around 3 dB near 1800 Hz in the left channel only, followed by a narrower stereo cut of about the same depth, in a second stacked EQ.
While my problem seems to reside in my left ear, attempting to correct only the left channel may knock out the condition when listening only to left channel sounds. But as soon as stereo listening resumes, there is still a bit more to knock out. I think that is brain crossing sound. Despite my clearing up the condition solely on the left, the right has some sympathetic hyper-recruitment, and you may need some mild treatment in both channels anyway.
While an annoyance at first, it is really a good kind of problem to have. It means you have restored your hearing to the level where you can actually discern these kinds of faint annoyances in the sound.