Do words differing only in the voicedness of consonants act as functionally homophonous? In Japanese, there are some sound differences that clearly distinguish words from one another, such as falling on a different or on the ([]{} vs. []{} or []{} vs ); while other sound differences make no difference as all (English 'l' vs. English 'r', vanishing `<u>` sounds, vs. ). Where on this spectrum does voicedness (e.g. vs. ) fall? (I am aware that words are spelled one way or the other, but then you get situations like []{} vs. []{} where the is _clearly_ the same word, or the somewhat more extreme []{} vs []{}.)

No, Japanese is full of voiced-unvoiced minimal pairs. There are minimal pairs even when the constituent morphemes are the same:

* mountains and rivers (dvandva compound)
* mountain rivers (modifier-head compound)



Dvandva compounds typically don't trigger rendaku, so the former is unvoiced. You can find plenty of other minimal pairs showing contrasts in voicedness, for example:

* mosquito
* moth



And so on. The important point is that native speakers hear these as clearly contrasting words, so it's a fundamental distinction in Japanese phonology. They are not homophonous in any sense.