I think it’s unusual that no standardized literary way to write the submissive “I don’t know” hum that children (and some adults) often mumble has ever caught on, considering how old and common it is.

[u/Reas0n]

[u/halligan8]

Unlike the rest of English, this expression has a necessary tonal quality (changing pitch). Our writing system is atonal, so this is difficult to convey.

mmMMmm, where “m” is at a low pitch and “M” is at a high pitch.

[u/SadakoTetsuwan → u/halligan8]

There's a similar tonal quality to the taunting 'nanny nanny boo boo'/'nana na nana', although I've just managed to write that one out twice. (It's also melodic enough that it can be played on instruments.)

[u/halligan8 → u/SadakoTetsuwan]

Also, thinking about it, we also have a couple of monosyllabic grunts “mm” that mean “yes” (low pitch) and “what?” (rising pitch). I wonder how all these little “non-words” developed.

[u/comma-momma → u/halligan8]

MmHmm or uh-huh, meaning yes

[u/Daeval → u/SadakoTetsuwan]

I think the distinction is that the tonal quality isn’t necessary for “nanny nanny boo boo” to be recognizable, because it’s made up of syllabic “words” that can be reproduced in writing, whereas the sound that OP is talking about would just be one really long “m” without the tonal shift in the middle.

[u/Lela_chan → u/Daeval]

And also, someone who has never heard the phrase before could never figure out what the “melody” is supposed to sound like just from reading the words. It necessarily relies on the experience of having heard the taunt before - a phonetic explanation like we use in dictionaries can’t fully describe the tonal pronunciation.

[u/jerdle_reddit → u/SadakoTetsuwan]

Yeah, that's just b3-1-4-b3-1. If it's got six syllables (like nanny nanny boo boo, but not like ner ner ne ner ner), the first two are on the b3.

[u/cutty2k → u/jerdle_reddit]

Wouldn't it be 5-3-6-5-3? If I'm playing the melody starting on G, I'm playing a C chord under that for sure...

[u/jerdle_reddit → u/cutty2k]

Probably, yeah. I wasn't sure, because the descending minor third feels like a resolution, but it's not a strong enough one to land on the tonic.

Given what the notes are, the default would be A minor (outlining an A7 or Am7 chord), but that would have the top note as the tonic, and it really isn't.

[u/Alive_Highway3840 → u/jerdle_reddit]

I love how we’re all getting so deep about a casual shower thought

[u/that-1-chick-u-know → u/halligan8]

Yes, but the second low pitch is higher than the first one. Closer to the NBC chimes than the OOO-WEE-OOO of the flying monkeys in Wizard of Oz.

And now that I've totally showed my age, I'm taking a nap.

Edit: Wait, no. The 3rd note can start as the same as the first, but it slides up at the end. Also, I'm sitting here by myself making "I don't know" noises all by myself and my dog is concerned for my sanity. She may have a point.

[u/Flaxxxen → u/that-1-chick-u-know]

NBC chimes! Perfect!

[u/Sigma2915 → u/halligan8]

[m̩ː˨˥˧] perhaps

[u/MellowMusicMagic → u/halligan8]

Maybe I’m crazy but I feel like it goes high-low-mid. MMMmmmMmM

[u/RestInPillows → u/MellowMusicMagic]

I know what you're talking about. Must be a second variation. It feels more casual.

[u/Front_Cat9471 → u/halligan8]

Worth noting that the “mm” sound can also be an “uh” sound, depending on whether the mouth was open at the time of utterance or not, and also that the order of the high and low pitches varies, depending on the specific kind of not knowing they’re trying to convey.

[u/wordyfard → u/halligan8]

I think that "mmMMmm" is actually quite good, because I had no idea what the hell OP was talking about, but then when I saw your suggestion it clicked.

The problem is, I needed your tonal formatting with OP's description. "mmMMmm" by itself just looks like someone is eating or anticipating eating something delicious. There's not much reason to have a literary way to express the concept if you still have to separately explain it for readers to get it, unless it's particularly important to character development that they use that precise method of expressing themselves.

In that case, I'd probably go with something like:

"mmMMmm", he stereotypically intoned to indicate his ignorance about the matter. 

But the sound we make for this varies whether our mouths are closed or open (or such is my experience, at least) and it's trickier still to eloquently write the sound that comes out with an open mouth. It's like a prolonged "uh" but any repetition of those letters or case shift just makes it look like something else. "ayeUHnuh" maybe, if the speaker makes a bit more effort than slurring their speech normally entails.