Introduction to Acoustics

tional rather than absolute (à la tone intervals defined as
frequency ratios).
Speech is rather a set of movements made audible
than a set of sounds produced by movements [16.14,
p. 33].
In keeping with this classical statement, many investigators
have argued that speech entities are to be found
at some upstream speech production level and should be
defined as gestures [16.170–173].
At the opposite end, we find researchers (e.g.,
Perkell [16.163]) who endorse Roman Jakobson’s view
which, in the search for units gives primacy to the perceptual
representation of speech sounds. To Jakobson
the stages of the speech chain form an “ ... operational
hierarchy of levels of decreasing pertinence: perceptual,
aural, acoustical and articulatory (the latter carrying no
direct information to the receiver).” [16.174]
These viewpoints appear to conflict and do indeed
divide the field into those who see speech as a motoric
code (the gesturalist camp) and those who maintain
that it is primarily shaped by perceptual processes (the
listener-oriented school).
There is a great deal of experimental evidence for
both sides, suggesting that this dilemma is not an
either–or issue but that both parties offer valuable complementary
perspectives.
A different approach is taken by the H & H (Hyper
and Hypo) theory [16.175, 176]. This account is
developed from the following key observations about
speaker–listener interaction:
1. Speech perception is always a product of signal
information and listener knowledge;
2. Speech production is adaptively organized.
Here is an experiment that illustrates the first claim
about perceptual processing. Two groups of subjects
listen to a sequence of two phrases: a question followed
by an answer. The subject groups hear different
questions but a single physically identical reply. The
subjects’ task is to say how many words the reply
contains.
The point made here is that Group 1 subjects hear
[Ð�×� �a�Ú] as“less than five”. Those in Group 2 interpret
it as “lesson five”. The first group’s response
is “three words”, and the answer of the second is
“two words”. This is despite the fact that physically the
[Ð�×� �a�Ú] stimulus is exactly the same. The syllabic [�]
signals the word than in one case and the syllable –on in
the other. Looking for the invariant correlates of the initial
consonant than is doomed to failure because of the
severe degree of reduction.
The Human Voice in Speech and Singing 16.8 Control of Sound in Speech and Singing 705
To proponents of H & H theory this is not an isolated
case. This is the way that perception in general
works. The speech percepts can never be raw records of
the signal because listener knowledge will inevitably interact
with the stimulus and will contribute to shaping
the percept.
Furthermore, H & H theory highlights the fact that
spoken messages show a non-uniform distribution of
information in that predictability varies from situation
to situation, from word to word and from syllable to
syllable. Compare (a) and (b) below. What word is likely
to be represented by the gap?
1. “The next word is .”
2. “A bird in the hand is worth two in the .”
Any word can be expected in (1) whereas in (2) the
predictability of the word “bush” is high.
H & H theory assumes that, while learning and using
their native language, speakers develop a sense of
this informational dynamics. Introducing the abstraction
of an ideal speaker, it proposes that the talker estimates
the running contribution that signal-complementary information
(listener knowledge) will make during the
course of the utterance and then tunes his articulatory
performance to the presumed short-term listener
needs. Statistically, this type of behavior has the longterm
consequence of distributing phonetic output forms
along a continuum with clear and elaborated forms
(hyperspeech) at one end and casual and reduced pronunciations
(hypospeech) at the other.
The implication for the invariance issue is that the
task of the speaker is not to encode linguistic units as
physical invariants, but to make sure that the signal attributes
(of phonemes, syllables, words and phrases)
carry discriminative power sufficient for successful lexical
access. To make the same point in slightly different
terms, the task of the signal is not to embody phonetic
patterns of constancy but to provide missing information.
It is interesting to put this account of speech
processes next to what we know about singing. Experimental
observations indicate that singing in tune
is not simply about invariant F0 targets. F0 is affected
by the singer’s expressive performance [16.177]
and by the tonal context in which a given note is
embedded [16.178]. Certain deviations from nominal
target frequencies are not unlike the coarticulation and
undershoot effects ubiquitously present in speech. Accordingly,
with respect to frequency control, speaking
and singing are qualitatively similar. However, quantitatively,
they differ drastically. Recall that in describing the
dynamics of vowel reduction we noted that formant fre-
Part E 16.8