It takes a certain sound level to engage me in the music. When I’m not engaged, I would prefer no music to music. There is probably some psycho-acoustic explanation.
As I age, I raise the sound volume levels even more, as if to compensate for something that is missing. Curiosity peaked, a simple internet hearing threshold test shows that I suffer from natural, age-related, degenerative, high-frequency hearing loss. This condition derives from loss of hair cells within the cochlea. Hearing loss is the world’s number one sensory disorder, affecting over 500 million humans, and projected double that in 50 years.
Some research suggests that primitive tribes away from modern civilization do not experience such a sensorineural hearing disorder. They live their lives without much high-frequency input to their ears. The ear may be a perverse case: use it and lose it. Most human hearing gradually diminishes after age 8. After age 20, the downhill slope steepens. By 85, any remaining mid-high frequency response will be down over 70dB. And the new generations will likely fare even worse due to their music listening habits.
Interestingly birds are the only other Animalia Class, besides mammals, with a cochlea. Even more interesting, birds can regenerate cochlear hair cells throughout their life, while mammals cannot regenerate these cells much after the fetal stage. There is research being undertaken in the search for transgenic and other mitigation for sensorineural high-frequency hearing loss in humans. Initially it was thought that females were spared some of the hearing loss, although no reason was discovered. A recent study has not found a sex-related difference. We’re all in the same boat.
The upshot is that people in mid-life or later should become interested in equalization compensation to help them hear all the music has to offer. The days of eliminating all tone controls from the audio circuit to ensure pristine sound are gone forever, because we can no longer hear the pristine sound. We need help. My audibility threshold curve was a shock; I have severe attenuation by 8kHz. I console myself because no musical instruments I will ever likely be exposed to can exceed a 7kHz primary tone. Now that the initial shock has subsided, I have learned my hearing is still somewhat above the average reported for my age.
Rather than jumping straight to hearing aids, or buying an expensive outboard equalizer, I looked around at my primary audio sources. In my study, I listen to music via iTunes, and my keyboard piano sounds are generated by the Ivory II software. Both Ivory and iTunes have built-in digital equalization, enabling equalization at the source. Ivory provides boost up to a 24dB in the form of a shelf on the high and low frequency end, with an added single parametric band in the middle; iTunes provides a graphic equalizer with up to 12dB boost at selected frequencies.
I wondered to what extent these EQ levels would successfully compensate for my loss. I enabled the iTunes equalizer and ramped up the loudness above 2kHz and below 250Hz, then did some A/B comparisons. I was blown away by how lifeless and quieted the unequalized sound was. I have been living in audio squalor, probably for at least 10 years unbeknownst, all the while trying to restore the missing sound with just the volume knob. It wasn’t working.
My hearing response is still pretty accurate in the middle range, staying within 3dB from 185Hz to over 3kHz. But at 4kHz, my ear hears a sound that is 27dB softer than the mid-tones. At 6kHz, it is 48dB softer; at 8kHz, 60dB softer; at 12kHz, 75dB softer. At higher frequencies, normal hearing also hears a softer tone, so that my hearing does not need quite this much boost to seem natural. But still, these values overstate the needed boost by at most 10dB. My source equalizers are not designed for such large amplifications, so I am not going to get full fidelity restored much beyond 4KHz just using the source EQ. But the difference is so remarkable that I am happy with what there is.
My ace in the hole is a DSP unit I bought years ago that has been lurking in my synthesizer rack. It offers dynamic equalization (DEQ), a more sophisticated EQ algorithm. At low sound volume (signal amplitude), hearing sensitivity at the very high and low frequencies is diminished relative to mid-frequencies. Hearing sensitivity increases to a more balanced, full-frequency sensitivity at moderate to high sound volume. Thus the most accurate equalization will vary dynamically with the amplitude of the input audio signal, where the amount of variation at any input volume is frequency-dependent.
In order to compensate for hearing loss at high frequencies, the audio signal must boost gain in this range. The DSP unit provides a parametric equalizer function that provides +15dB gain, which can be applied in a high shelf mode to frequencies above, say 2.5kHz. Using the maximum 12dB/octave slope, this gives +12dB at 5kHz. Such gain at frequencies over 3kHz may seem harshly bright during higher volume passages. This is where the DEQ equalizer enters the processing chain, reducing the gain in upper frequencies during dynamically loud passages, and providing unfettered gain during quiet passages.
All this technology is for my private listening, since younger listeners would not appreciate all the added high frequency oomph. On the shared media stage, I brighten the sound modestly using the built-in equalizer in the AVR component. Normally, this is for tuning the speaker response to the room, but I simply use it to add a +6dB shelf above 4kHz to help me hear a bit more of the highs and to ease understanding of the spoken word better in quiet passages of movies (the consonants are the first sounds we lose). For digital music, iTunes has already boosted the high shelf frequencies by +12dB, so we can enjoy substantially reconstructed mid-treble response to match the fall-off of our aging ears.
Ultimately, we elders will hope to get some audiophile hearing aids, i.e. bionic ears, so that live entertainment and uncompensated audio playback can be fully appreciated. Without hearing aids, live music will be increasingly muffled and lifeless. Special music listening programs have been offered by some hearing aid manufacturers that can amplify sound at all frequencies up to 10kHz, and only compress sound after 110dB. These frequencies and sound levels are considerably beyond the capabilities of most hearing aids designed for speech understanding, but are the minimum specifications for an audiophile hearing aid. But most reviews reveal that such state of the art hearing aids do not reach audiophile standards, and that the market is pulling away from supporting music listening with hearing aids. Thus listening at home on our audio rigs with equalization will provide the most music appreciation we can hope for.
My 60’s playlist currently has over 375 tracks, more than 21 hours of the music I used to listen to in my 20s, 1963-1972. They don’t seem to be writing them like that anymore. And now I’m hearing them more like I did back in the day. It was a good time.