On Lingua Franca today, Allan Metcalf of the American Dialect Society has a cute piece on dialect description citing numerous examples of different regional dialects being characterized by the same layperson's description: the utterly undefined but oh-so-popular phrase "nasal drawl." They come from from all over: Missouri, Philadelphia, Brooklyn, California, Massachusetts, the Deep South, Texas, Chicago, anywhere. There's no phonetic reality to this imaginary sound quality: Metcalf says "If you want to say something specific about a person's pronunciation but aren't too comfortable with phonetic terminology, you can say 'nasal drawl' and people will understand. It means—well, it's hard to say what it means…" It's only language you're talking about; just make stuff up.
This is what we get from writers' descriptions of regional accents they don't care for, in a world where almost no one ever takes even an elementary course on linguistics or phonetics while they're in college, but everyone who writes a book thinks they know enough about language to give effective descriptions of it. (Notice Mark Liberman's remark here: "In my experience, 'nasal quality' almost always means 'low-frequency sound qualities that I don't expect, from people that I don't sympathize with'." And note the excellent example in the associated post of what it's like when a real expert in phonetics has a shot at describing vocal quality.)
It's as if diseases from cirrhosis to appendicitis to colon cancer were being described by novelists as "the colick", and everyone just accepted that and imagined it was an accurate diagnosis. Or as if you could always describe a dog you didn't like as "a mongrel bitch" without any risk of someone saying, "What do you mean? That's a male Irish wolfhound."
I'm not suggesting that novels would be improved by adding paragraphs about pitch pulses, diplophonia, and near-infrasonic amplitude modulation; I'm just pointing to the fact that in descriptions of speech you can always get away with repeating random descriptive phrases that don't mean anything. Read the whole of Metcalf's piece here.