Can You Measure Why a Sound Is Unpleasant?
Short answer: Partly. A number can't tell you whether a sound is beautiful. It can tell you how a sound you dislike differs from one you like. I measured four simple things in two of my sound worlds, and the differences pointed straight at what to fix.
The problem with "it sounds bad"
My Space world sounded wrong for a long time. Sharp. Thin. Tiring after a few minutes. Ocean, built with the same engine, was fine.
I could hear that something was off. I couldn't say what, which meant I couldn't fix it. I kept changing things by ear and going in circles.
The idea that helped
I'm no audio engineer, and a measurement on its own meant nothing to me. What worked was comparing. I took the same few measurements of Ocean, which I liked, and of Space, which I didn't, and looked at where they disagreed.
There were four. None of them needs any maths to understand.
1. Where the weight is
How much of a sound sits in the low end? In Ocean's harmony, about half of it did. In Space's, almost none.
That explained "thin" and "not deep" in one go. It also explained why my fixes had failed. I had been trying to filter Space into sounding deeper, and a filter can only remove things. It can't add a low end that was never there. A lower tone under each note can, which is the subject of where "deep" comes from.
2. How fast a sound starts
How long does a sound take to reach full loudness? The worst of Space's short sounds got there almost instantly. The pleasant sounds in Ocean and Forest took many times longer.
A start that fast is heard as a click, whatever comes after it. I wrote about that in why a fast start turns into a click.
3. How far the peak sticks out
This one has a name: crest factor. It compares the loudest instant of a sound with its average level. Wikipedia says it "indicates how extreme the peaks are in a waveform".
The same nasty sound had a huge spike at the front and almost nothing after it. So what reached the ear was a loud click with no body behind it. That is "sharp" described as a number.
4. How bright it is on average
This also has a name: spectral centroid. Wikipedia says it "indicates where the center of mass of the spectrum is located" and calls it "a good predictor of the 'brightness' of a sound".
Think of it as the balance point of a sound between low and high. Several Space sounds balanced much too high. A passing band of noise came out as a bright hiss. A plucked note came out as a twang. I pulled both down until they balanced nearer to where Ocean's sounds do.
What the numbers did and didn't do
My ears had told me what was wrong: sharp, thin, tiring. The measurements told me why, and that gave me something to change.
They did not tell me when to stop. After each change I still had to listen. A sound can match a pleasant one on all four counts and still be dull.
So I wouldn't call this measuring unpleasantness. It is measuring the distance from something I already know is pleasant. For a beginner, that was enough to stop going in circles.
Sources
Try it: Open Ambient Sound Online and listen to Ocean, which is free. It is the world I measured everything else against.
Open Ocean, free