Why do certain vocal melodies work in context when those same melodies would sound dissonant on instruments?

Question

I've been transcribing more vocal lines lately in songs I like, to go along with the usual instrument transcription I do, and I've noticed something interesting - a lot of my favorite vocal parts clash very very noticeably with other instruments in the song when that melody's played back by an instrument, but they sound perfectly fine, consonant, even, when performed by a vocalist. There are multiple dimensions to this clashing - usually there's some rhythmic clashing (vocal parts are often polyrhythmic when compared to instrumentals) and harmonic clashing (voice-crossing, dissonant intervals, microtonal shifts, to name a few, often in the same range as other instruments).

At first I thought that maybe I was transcribing the vocal melody in the wrong octave, maybe one octave too low, but after more careful listening that wasn't it.

Why / how could this be the case? What is it about the human voice that makes it possible to get away with clashing vocal melodies that'd just sound like a hot mess or noise if played on any instruments instead? Or is there something in the way the melodies themselves are constructed that makes them work with the human voice in this way?

Answer 1

I suspect two primary reasons for why a melody that sounds decent in voice sounds terrible on an instrument when it's played against the same background music:

1. The timbre of the human voice is distinctly different from the timbres of instruments. It's possibly an extreme version of how some synths just sound completely terrible (the worst one I remember is the synth melody of Necrodeus's theme in Kirby Mass Attack). Maybe some melodies do sound just that much better in the human voice.

2. A human voice can microtonally adjust individual notes in the melody on the fly. This varies from adding vibrato to using smooth glissandos to tweaking how flat G#/Ab is depending on whether it's used as G# or Ab. Instruments typically aren't capable of pulling off all of these on the fly (the piano can't get re-tuned that quickly, flutes can't continuously glissando like a trombone can, the harpsichord needs tremolos instead of vibrato), so they can't play some melodies quite like the human voice can.

Answer 2

You've got the words to latch onto. And a voice can do anything between completely un-melodic rapping and full lyrical singing. We tolerate it at the halfway point!