When comparing frequency patterns(e.g. using an FFTSCOPE) for spoken vowel sounds and that of consonants, some of us found vowel sounds to have more overtones(i.e., a larger number of peaks in the power spectrum) than consonants while others found the opposite. Is there a correct answer for this question or does it depend on an individual's way of pronouncing them?
Consonants are primarily just noise—largely high, semi-random frequencies. Vowels are generally the only part of speech that have harmonic content as opposed to the inharmonic content of consonants. Bright, forward vowels like EEEEEE have way more overtones than dark, back vowels like AHHHHHH. Most consonants other than the nasals are so brief that I'd be surprised if any overtone content can be seen at all that relates only to them—the overtones would surely mostly come from any preceding and following vowels. Again, the nasals like mmmmm and nnnnnn are an important exception, and I would expect fairly strong overtone content from them.
Otherwise, the fricatives and especially sibilant plosives should cause brief bursts of more-or-less random high-frequency blasts that might look like "more overtones", but are actually just noise.
It depends on your way of quantifying matters. Normal speech converts airflow into energy somewhat efficiently so you have similar amounts of energy per time. Consonants fall into several different classes, voiced and unvoiced, and orthogonally nasal, fricatives, and plosives.
Vowels are directed rather well, so they tend to carry better than most consonants in the direction of talking. Particularly if they are well-supported with a relaxed low larynx. The unvoiced components of fricatives and plosives are basically all across the spectrum, with the fricatives having random phase (distributing energy evenly across time) and the plosives linear phase (focusing a high amount of energy to one point of time). Vowels have a line spectrum, with the first line being the fundamental frequency and additional lines being shaped out of the harmonics by the vowel tract. The lines obviously have higher peaks than the broad spectrum unvoiced sounds. There are more harmonics to start before shaping when there is good vocal closure and/or chest voice involvement.
Flute/Falsetto registers are weak in harmonics for formants to start with, and the vowel tract is more apt shaping the harmonics at lower pitches, so vowels become badly distinguishable in those registers.
In operatic settings, consonants tend to get lost, partly due to their worse directivity, partly because particularly fricatives are limited in volume, and plosives need more conscious exaggeration than vowels. I've witnessed an American "Siegfried" who was basically vowels-only. Totally annoying.
So it very much depends on the windows in frequency and time that you are considering to figure out where most energy is available/focused.
The important point here is less the vowel/consonant definition, but more the phonetic sound that they represent. E for Example can be from eeeeeexample, or seeeee, which have a different set of overtones
consonants work to punctuate the vowels and give shape to the language because they are mostly short bursts of density. They have generally more overtones in a short space of time which allows your mind to pick them up.
At their simplest you have Open Vowel sounds like AAAAAAAh, EEEEE etc
then you have Nasals in the middle, like mmmm or nnnnn
I believe a sound which can't be sustained is called a plosive. So T for example
I took a spectrometer recording of a T(as in Ticking) sound against an E(as in speech) sound and found that the T sound had far, far more overtones packed into a small space. (I'll post the image in a bit)
Think of it like an opera singer hitting a long sustained note(say e) vs a snare drum. The Snare Drum is a short sharp burst of sound like a plosive, but it penetrates the long sound because there're a lot of overtones hitting at one short burst.
Then you have the weird sounds like (Mira)ge, or the ch in Loch.
Hope that helps :)