Formant Characteristics of Human Laughter
Fascinating.
NoisyLittleBugger
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Vowel Sounds
The term formant refers to peaks in the harmonic spectrum of a complex sound. They are usually associated with, but not necessarily equal to some sort of resonance of the source. Because of their resonant origin, they tend to stay essentially the same when the frequency of the fundamental is changed. Formants in the sound of the human voice are particularly important because they are essential components in the intelligibility of speech. For example, the distinguishability of the vowel sounds can be attributed to the differences in their first three formant frequencies. Producing different vowel sounds amounts to retuning these formants within a general range of frequencies. Benade suggests the following ranges of frequencies for the formants of a male voice:
1st formant 150-850 Hz
2nd formant 500-2500 Hz
3rd formant 1500-3500 Hz
4th formant 2500-4800 Hz
The process of articulation determines the frequencies of the vocal formants. Sundberg has identified portions of the vocal anatomy which he associates with the formant frequencies. The jaw opening, which constricts the vocal tract toward the glottal end and expands it toward the lip end, is the deciding factor for the first formant. This formant frequency rises as the jaw is opened wider. The second formant is most sensitive to the shape of the body of the tongue, and the third formant is most sensitive to the tip of the tongue.
via Vowel Sounds
How the Vocal Tract Filters Sound
The two largest spaces in the vocal tract, the throat and mouth, therefore, produce the two lowest resonant frequencies, or formants. These formants are designated as F1 (the throat/pharynx) and F2 (the mouth). In singing or speaking, it is these two lowest formants that are controlled by shaping the resonant areas with lip and tongue movements to produce vowels.
Formant-based synthesis of singing
Rule-driven formant synthesis is a legacy technique that still has certain advantages over currently prevailing methods. The
memory footprint is small and the flexibility is high. Using a
modular, interactive synthesis engine, it is easy to test the
perceptual effect of different source waveform and formant
filter configurations. The rule system allows the investigation
of how different styles and singer voices are represented in
the low-level acoustic features, without changing the score. It
remains difficult to achieve natural-sounding consonants and
to integrate the higher abstraction levels of musical
expression.
Index Terms: formant synthesis, singing
Synth Secrets, Part 23: Formant Synthesis
VOWEL SOUND AS IN… F1 F2 F3
“ee” leap 270 2300 3000
“oo” loop 300 870 2250
“i” lip 400 2000 2550
“e” let 530 1850 2500
“u” lug 640 1200 2400
“a” lap 660 1700 2400
Finally, let’s take a look at how the FS1R imitates the frequency response of a harmonically rich signal (or noise) passed through a resonant low-pass analogue filter (see Figure 16, above right). Yes, yes… we’ve seen it all before, but bear with me one more time.
Surprisingly, we can reconstruct this frequency response using just two formants — one with a centre frequency of 0Hz and a Q of, say 0.1, and one with a centre frequency equal to the analogue filter’s Fc, and with a Q of, say, 10 (see Figure 17, right).
The result is remarkable. What’s more, we can make the formant-generated sound respond very similarly to the analogue case. To be specific, we can shift the perceived cutoff frequency by moving the centre frequency of the upper formant while narrowing the Q of the lower formant by an appropriate amount. Do this in real time, and you have a sweepable filter. Furthermore, we can increase and decrease the perceived resonance by increasing or decreasing the amplitude of the upper formant alone.