The article is extremely muddled from a technical point of view. When dealing with perceptions it is extremely important to distinguish physics and physiology. In optics we have radiometric (physical) vs photometric (perceived) values: https://en.wikipedia.org/wiki/Photometry_%28optics%29#Photom...
It appears in the article they are doing some kind of implicit averaging over the ear's response function at each frequency, which may make sense in terms of perceptions but makes very little sense in terms of physics.
A much better visual analog would be a blurred photograph rather than a cropped one. "Turning up the volume" simply increases the brightness of the images, which doesn't do a damned thing to reduce the blurring.
One thing that people with normal hearing don't get is how much information is in the high frequencies, which are where the most loss normally occurs, although there are also "notch" losses that happen to people whose ears are routinely subject to loud noises in narrow bands.
We tend to think of "high frequency" sounds in terms of single notes, but in speech the high frequencies are most important in the unvoiced constants, the "s" and "th" sounds and similar. Losing the high frequencies blurs the edges of speech, often making the shape of it unrecognizable. Frequency-dependent enhancement sharpens the edges and brings it back into useful focus.
