IPA for ふーん/んふふ pronounced with your mouth closed


I know that ふ is normally pronounced as [ɸɯ]. But ふ is sometimes used to
represent a clearly different sound that occasionally appears in spoken
Japanese, and I'm having trouble identifying its IPA representation.

The following is what I know about this sound:

  * It does sound like the h consonant to me, but it can be produced **with your mouth completely closed**.

  * No normal Japanese word contains this sound, but a few interjections and onomatopoeias like ふーん, ふふんっ, んふふ, ふっふっふ, ふがふが are often pronounced with this "sound".

  * It's the very first sound in [this video](https://www.youtube.com/watch?v=NTeYVAomFxs). It's written as **ふ** ーん but it's obviously not [ɸɯ].

  * [Japanese Wikipedia suggests](https://ja.wikipedia.org/wiki/%E3%81%B5) this sound is 無声鼻腔摩擦音 ("voiceless nasal fricative"?).

> 無声鼻腔摩擦音を「ふ」で表すことがある（例：「ふん」と鼻で笑う）。

But the article gives no IPA representation, and this term appears nowhere
else in Wikipedia.

  * I think English "hmm" and "humph" have a similar sound, and some sources including [this](https://www.reddit.com/r/linguistics/comments/1p05nn/how_would_you_ipatranscribe_hmm/) suggest this sound is [m̥] (the voiceless version of [m]). But other sources including [this](https://www.youtube.com/watch?v=CcSsEbwyBFk) and [this](https://en.wikipedia.org/wiki/Voiceless_bilabial_nasal) seem to suggest [m̥] is a rare consonant.

So what is this sound in IPA? How do you transcribe ふーん and んふふ said with your
mouth closed?




When we say //ha// or //ho//, the actual phonetic realization of the //h//
sound is _the same as the following vowel, but voiceless_. In other words, we
could potentially choose to transcribe [[hɑ]] as [[ɑ̥ɑ]], with a ring
diacritic under the first vowel to show that it's been devoiced.

Likewise, English _hmm_ //hm// can be transcribed phonetically as [[m̥m̩]].
The English interjection _uh-huh_ //mhm// is typically pronounced [[ʔm̩m̥m̩]]
when your mouth is closed, with a short voiceless period separating the two
syllabic nasals. If you pronounce this word slowly, you'll notice that you're
making the same sound, just stopping and starting the vibration of your vocal
folds partway through. Aside from the opening and closing of the vocal folds,
nothing else is changing, so it's hard to say that [[m̥]] is an incorrect
transcription.

As long as we're talking specifically about interjections, [[m̥]] is not
really such a rare sound, but then, interjections are special in many ways. In
Japanese, the interjection うん //ɴ// is typically pronounced [[ʔɴ̩ː]] or
[[ʔm̩ː]], but outside of interjections Japanese words are usually considered
not to begin with //ɴ// due to phonotactic constraints. This is another way
that interjections are special.

I see no reason not to transcribe the sound in question as [[m̥]] if your lips
are closed, as in ふーん [[m̥m̩ːː]] and んふふ [[ʔm̩ːm̥m̩m̥m̩]].




When we say //ha// or //ho//, the actual phonetic realization of the //h//
sound is _the same as the following vowel, but voiceless_. In other words, we
could potentially choose to transcribe [[hɑ]] as [[ɑ̥ɑ]], with a ring
diacritic under the first vowel to show that it's been devoiced.

Likewise, English _hmm_ //hm// can be transcribed phonetically as [[m̥m̩]].
The English interjection _uh-huh_ //mhm// is typically pronounced [[ʔm̩m̥m̩]]
when your mouth is closed, with a short voiceless period separating the two
syllabic nasals. If you pronounce this word slowly, you'll notice that you're
making the same sound, just stopping and starting the vibration of your vocal
folds partway through. Aside from the opening and closing of the vocal folds,
nothing else is changing, so it's hard to say that [[m̥]] is an incorrect
transcription.

As long as we're talking specifically about interjections, [[m̥]] is not
really such a rare sound, but then, interjections are special in many ways. In
Japanese, the interjection うん //ɴ// is typically pronounced [[ʔɴ̩ː]] or
[[ʔm̩ː]], but outside of interjections Japanese words are usually considered
not to begin with //ɴ// due to phonotactic constraints. This is another way
that interjections are special.

I see no reason not to transcribe the sound in question as [[m̥]] if your lips
are closed, as in ふーん [[m̥m̩ːː]] and んふふ [[ʔm̩ːm̥m̩m̥m̩]].

