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subharmonics and roughness

Hi! My name is Chen-Gia Tsai <gia@snafu.de>, and as my name shows I am from
Taiwan. I hold a B. A. in Physics and obtained my Master degree from the
National Institute of the Arts, with an thesis on a Taiwanese folk opera:
Luan-Tan. After living one year in Europe, I switched my interests from
ethnomusicology to *hard* science, e.g. musical acoustics, psychoacoustics,
neuromusicology, physiological acoustics and even bioacoustics. Currently I
am a doctoral student at the Musicology Department at the
Humboldt-University in Berlin. My dissertation will be an
acoustic/psychoacoustic study of the Chinese flute.

I am writing to discuss subharmonics in human voice. It is puzzling that
voices with subharmonics sound rough, because octave is a consonant interval
in music theory.It sounds very harmonic and pleasant.

Recently, some psychoacoustic models for the quantification of roughness are
applied on processing subharmonics in pathological voices (see below). But
not all voices with subharmonics sound rough. For instance, Tibetan monks
chant with fundamental pitch as low as 60 Hz. This singing technique (or
"chant mode" - see, for example,
http://www.sciam.com/1999/0999issue/0999levin.html), which is associated
with vibration of false folds, can be treated as controlled subharmonics.
Beside period doubling, period tripling is used in human singing (see
Gibiat, V. & Castellengo, M.: Period Doubling Occurences in Wind Instruments
Musical Performance. In: Acustica 86, 2000, S. 746-754.). Thus subharmonics
appears not only in pathological voices, but also in beautiful singing, in
music. It is my feeling that some sounds with subharmonics are rough, but
some are not. I have studied occurrences of subharmonics in Chinese
membrane-flute tones. They sound really rough for me. But my friend thinks
they sound not rough at all.

Since octave and fifth are consonant intervals, the relation between
roughness and subharmonics is quite puzzling. It might reflect the
complexity of roughness and consonance/dissonance.

[quote from J. Acoust. Soc. Am., Vol. 105, No. 2, Pt. 2, February 1999:1192]

3pSC1. Application of a roughness model to pathological voices.

Robert Reuter (Inst. Electron., Techn. Univ., Einsteinufer 17, D-10587
Berlin, Germany, rreuter@tubife1.ee.tu-berlin.de) and Hanspeter Herzel
(Humboldt Univ., D-10115 Berlin, Germany)

Irregularities in voiced speech are often related to the intrinsic
nonlinearities in the vibrations of the vocal folds. Desynchronization of
vibratory modes can induce nonlinear phenomena such as subharmonics,
biphonation (two independent pitches), and deterministic chaos. The
resulting complex signals exhibit various amplitude and frequency
modulations and are, therefore, perceived typically as rough voices. In
clinical studies of pathological voices perceptive roughness scores are
widely used. So far, however, no satisfactory correlation of ratings of
roughness and acoustic parameters has been found. In this presentation a
modified Aures model for the quantification of roughness is introduced. It
is exemplified that subharmonics lead to high roughness scores whereas the
roughness of biphonation depends strongly on the two frequencies. Finally, a
set of 120 perceptually evaluated pathological voices is studied. It turns
out that the roughness score obtained from the psychoacoustic model is
stronger correlated to the ratings of phoniatricians than conventional
perturbation measures such as jitter and shimmer.


Chen-Gia Tsai