I have central auditory processing disorder, CAPD, which means that listening to words is always hard work. A mondegreen is "a mishearing or misinterpretation of a phrase as a result of near-homophony, in a way that gives it a new meaning." This is a daily occurrence for me. My hearing is always blurred; I do a LOT of guess work when I don't know someone's cadence, style, and vocabulary. Listening to people talk is easier if I know them well and have a subconscious catalogue of what words they tend to use, what letters they tend to emphasize or drop, etc.
If you have ever trained a device to learn your voice for voice-to-text, you know that you have to invest a good number of hours before the computer successfully translates your sound to text, and before that it is a muddled mess of nonsense. And if there is a lot of ambient noise -- especially sibilant noise like the rushing of wind -- the computer will get it wrong even if it usually gets it perfect. That's my brain.
I rely a lot on the length of words and logical possibilities for what could fit. An example: I hear someone say "-ee ay m|by --o|a-t|d-t|d --eem|n" while they hold an empty cup with white remnants in it and point at someone else. From this I guess that they are saying "he ate my clotted cream" but without context it could be "the gate by spotted beans" or "she may cry fated seams" etc. It sounds very nearly the same to me. Some words don't have a lot of sound-alikes that make sense to switch out, but a LOT of adjectives do, and adjectives can be stuck into a sentence almost anywhere. It's extra difficult when it's a three word sentence out of context with only an article in the middle, because "____ is ____" could be almost ANYTHING, and I can't even tell how long the missing words are. Also, I almost always miss the first word or two someone says to me, because I hadn't tuned in yet, so I have to allow for a missing word at the beginning.
This also means that short, out-of-context phrases can be nearly impossible for me to figure out within a reasonable conversational pause. The other day someone walked by and said "___ __ ___ __-" with some of these letters: h d g. I initially interpreted this as "have your good day!" since I was getting in my car and I replied "you too!" I got in my car, then realized the sound pattern was actually "___ ___ ___ __-__?" and they had asked me "how's your day going?" They mumbled the last bit so I didn't notice the last syllable, and I transposed the d and g accidentally. The "r" I heard but assumed I mis-heard at first.
Letters that weirdly sound the same, or sound the same in some accents:
fl-pl-bl-l (especially beginning a word)
tl-dl-fl (when inside a word)
o-u (cot, cut)
e-i (bid, bed)
oo-u (long u).
Letters/sounds that I can usually guess right: long a-e-i-o, short a (cat), k, j, g, hard c, l, q, x, and y, ow.
And a lot of people in the south drop their final g and r and t and b in consonant conjunctions so "passing your best curb pound stomp" becomes "passin yah bess curr poun- stom-," for instance, so wherever one of those might be tacked on I have to guess whether it should be there or not.
So, "have you heard that wild geese are flying west now?" would sound like "(-w|h*a|o|u*v|s|z) (w|y*oo-) (w|h*e|i*r-) (d|th|h*a*t|d|p) (y|w*i*l-) (g*ee*s-) (a*ah|r) (fl|l|bl|pl*y*ee*n|m|b-) (w|h*e|i*st) (m|n|b|w|d*ow-)?" I separated letters with asterisks and put each word in parenthesis but obviously when I hear it I don't get those markers -- it's even harder to read. The vertical lines mean that a sound could be any of those letters. The hyphens are dropped letters or places where dropped letters could be, based on the cadence of speaking. Without context I would have a VERY difficult time translating this. It could be "has your weird dad file-greased at lying best down?" and I only know it isn't because that doesn't make much sense. But also, if I hear it strongly like that, it makes it impossible to back up and re-run the sound to guess again because now that's all my brain wants to suggest.
Watching a person's face helps immensely, because I'm reading their lips and their expressions, which give additional context. If someone is very good at mouthing their words, I can understand them almost as well (or as badly) as I can when they're speaking aloud. Better than people who mumble! I realized this when watching people perform deaf poetry, some of whom mouthed the words very clearly. Even across the room, I could understand them better with no sound than someone who mumbles, even if they mumble loudly.
I have a co-worker who has an unpredictable speech pattern and also mumbles, and I mis-read them probably at least 3 times a week. Since we mostly communicate via text in chat and not audibly, that is a LOT. But at least I don't mind being laughed at, so I just repeat what I heard and that gets them to repeat it more clearly.
I used to make the mistake of asking people to repeat themselves and that is almost never effective, because with the same speed and inflection, getting louder does not help. And a lot of times they won't repeat, they'll rephrase or summarize, which frustrates my curiosity to no end. But if I tell them what I misheard, they will repeat it and put emphasis on the bits I didn't get, which is exactly what I need. It's less frustrating to them too, which is good because I don't like for people to associate me with frustration.
This is why I can't deal with ambient noise and conversation at the same time. Understanding sound as words takes so much mental processing and when there is any ambient noise it is twice as hard or sometimes literally so hard that it is impossible. I can't have music with lyrics on at the same time as I write, read, or listen to anyone speak, because my mind automatically tries to translate it and it takes up all my ability to think. I really miss being able to listen to lyrical music while reading or writing or spending time with people, but I don't think I will ever have that again.
It hasn't always been this way and I am not sure why it got worse, but I do remember listening to music about three years ago and realizing that it sounded different. I think my brain now has a hard time with any sibilance (shhh and ssss sounds) so I don't like music with cymbals any more. With songs I already know well, I can handle it because since my brain knows the lyrics it doesn't have to work as hard but I can't do any new music with a bunch of sibilance and I rarely even want to listen to the songs I've loved for decades if they have that sound.
This rules out practically all rock and a lot of folk -- anything that uses metal striking metal or a shaken instrument (especially cymbals and tambourine) as well as a lot of violin / fiddle or viola (cello is still okay because of the low pitch). To hear it feels like someone is scraping my eardrum with something sharp. It might be okay without lyrics? it may be that it's the combination that my brain can't handle, but most of that sort of music doesn't come without lyrics, so I don't know.