Asymmetric Hearing?



Some of us have asymmetric hearing, found either from audiology, or else it is quite obvious to us.

What I have found across a sample of about a hundred individuals over the past decade, is that unless the asymmetry is severe, as in conduction loss that is substantial on one side, a single correction applied to both ears usually suffices, or is actually preferred. Why should that be?

I can only speculate that, because we know that sound crosses over from each side in our brain processing, maybe we have learned to accommodate the asymmetry, and our brains have a way of equalizing the sound for us.

People with mild asymmetry always seem to choose the same setting for left and right, despite their asymmetry – at least for when they listen to music through Crescendo. Perhaps an asymmetric setting, which should have balanced out the asymmetry, caused too much shift for their brain in restored symmetry, after it had long become accustomed to the asymmetry.

For those unlucky individuals with strong asymmetric conduction losses, I have found that underneath the conduction loss there is often only mild degrees of a sensioneural frequency profile. So for those people, what actually works best is the Balance control on their amplifier. Just make the sound on the worse side louder. If they have some sensioneural frequency shaping, then use Crescendo ahead of that Balance treatment.

I’m sitting here right now, experimenting on a variation of hearing asymmetry, where my left ear has a profoundly deep notch up around 1250 Hz, and my right ear is fine. You can detect these kinds of variations for yourself, either by playing notes on a chromatic scale, or else play a mono sine upward sweep signal into both ears at the same and close your eyes and try to visualize where the sound is coming from.

If you hear the sound running right up the middle then you have perfect symmetry in your hearing. But in my own hearing I hear the bass region as centered, then moving leftward, and then sharply veering rightward at the very highest frequencies. My notch is so narrow that I hardly notice it during the sweeps. I have to listen carefully to detect it during sweeps.

But going up the chromatic scale on a keyboard, where I can closely examine each individual frequency, I definitely find my notch. No doubt about it.

During music playback, that left notch makes it more difficult to hear the soft details in the upper octaves during a piano concerto. And that’s just too bad because there is nothing that anyone can do to restore profound hearing loss. Profound means that you can’t hear anything, even when the amplifier is cranked up to lethal levels. It’s just plain gone, and you’ll never get it back.

So, okay, I have to live with that. But there is another effect caused by that notch – namely, at around 1800 Hz, just above that notch, my hyper-recruitment kicks in for an equally narrow range. And that makes high strings and female chorus music produce a faint raspy, crunchy sound, right at the top end of the Pain Frequencies between 1-2 kHz. So it definitely stands out to me, even though it is faint.

Up to now, I have assumed that it only affected my left hearing, and not my right. But maybe that’s not quite right, because of that brain crossover I just mentioned. Is my hearing really asymmetric during music listening? Maybe not…

I set up the mixer to split the L/R channels into side buses, where I could independently apply EQ to the left channel. Then the two buses are recombined into output L/R channels for playback. That let’s me tune up Crescendo for the left side hyper-recruitment, without affect the right hearing around 1800 Hz.

But now, unless I disable the HdphX crossover, I still get some of the right channel feeding into my left ear. So, for now, for the sake of science, I’ll just have to forego HdphX for the duration of this experiment.

Crescendo does independent corrections for each ear, listening only to what each is trying to hear, and making adjustments suitable for that ear. And with a single knob vTuning control, I’ve told the system to use the same degree of correction levels for both ears. And that’s okay, because we do know that sound crosses over in our brains, and people always prefer that same setting. I do too, despite those quirky looking asymmetries in my audiology – I think those are just measurement errors, not true asymmetry.

But hyper-recruitment and decruitment are really handled outside of Crescendo, by sort of tricking Crescendo with an Equalizer into making suitable corrections for those conditions. That means that independent EQ on each side can work to correct asymmetric hyper-recruitment and decruitment. It just sort of works out the way I need it to for this experiment.

Now, I found a track that really tickles the crunchies for me, Jean-Michel Jarre’s Oxygen Part 6, with synthesized ocean waves crashing up on the beach in the background of the music. A sonogram of crunchy-stimulating sound looks like this:

You see those big, slow, sawtooth patterns made out of pink noise? Those are the coursing waves in the background. And my frequency scale is somewhat logarithmic, so the apex of those saw-teeth is right up there around 2 kHz, right at my hyper-recruitment hearing. They are biased to the left, as shown by the brighter display in the top (left) track. And that excites the faint crunchies in my left ear.

The crunchies aren’t very strong. I have to be really listening carefully to hear them. Sort of a minor irritation when I’m trying to hear something else in the music very critically. But they do distract, and I would like to conquer them.

Fiddling around with the Left EQ, it seems I need a notch of about 12 dB with a Q of 0.4. That’s a deep, and mildly broad, frequency dip that makes the crunchies disappear. And yes, my hearing really does seem to be asymmetric with respect to those crunchies. Splitting L/R channels and applying Left-only EQ is helping. I’m not hearing any crunchies in my right ear which is being fed the full spectrum without EQ.

Bear in mind that those of us with hearing impairment don’t hear EQ in the same way as other people. Even in this case, by preceding Crescendo with the notch EQ, I’m not damaging the sound the way it would for others. Anyone else would hear a hole in their music at 1.8 kHz.

And anyone else without hyper-recruitment like mine, would get the hole in the music after their hearing is corrected with Crescendo. So my hearing is doubly confounding here. But in general, in order to hear what everyone else hears with EQ means that you must perform the EQ ahead of Crescendo corrections.

What my EQ notch really does, in preceding Crescendo, is to trick Crescendo into producing toned down corrections for what is really a much stronger recruitment curve than anyone else with the same threshold elevation at that frequency. The corrections are stronger, but the music is forced to softer levels by the EQ, and so the result is just right for keeping hyper-recruitment under control. I never feel the discomfort that untreated hyper-recruitment causes. And my music sounds just right.

So, I can’t live without HdphX. Either I make it become a separate plugin so I can place it ahead of Crescendo and this asymmetric EQ, or else I’ll have to live with a bit of crunchies from the cross-feed.

But the results of the experiment are that it is useful to apply asymmetric EQ to correct for asymmetries in hyper-recruitment and decruitment.

  • DM

[ In fact… since the swept sine veers sharply rightward at the highest frequencies, it seems that my decruitment is confined to my left ear too. Could the notch be causing both conditions?

So here is my full EQ treatment on the left, nothing on the right:

It sounds TERRIFIC! ]

Author: dbmcclain

Astrophysicist, spook, musician, Lisp aficionado, deaf guy

Leave a Reply