Cancer Research in Switzerland - Krebsliga Schweiz

Renevey Philippe | Development of a voice restoration
system for laryngectomees in order to improve their
social interaction (OCS 01777-08-2005)
Laryngectomy denotes a treatment of laryngeal cancer requiring
partial or total removal of the larynx. The loss of
the vocal function is one of the very distressing consequences
of this pathology. Medical rehabilitation techniques
allow laryngectomees to partially recover vocal
function, but it results in poor voice quality and insufficient
speech intensity.
The main goal of this project was to develop speech signal
processing methods for the restoration of the voice
quality in laryngectomees’ speech. In particular, the proposed
scheme estimates parameters from the pathological
speech and uses a voice model to restore missing or
degraded voice characteristics. The naturalness and emotional
paralinguistic features found in healthy voices are
restored from different cues estimated from the pathological
voice. Healthy speech is then reconstructed by recombining
the previously estimated speech parameters
and the new voice source.
The procedure adopted for this project was initially based
on the enhancement and adaptation of existing speech
signal processing algorithms to the particular characteristics
of pathological speech. The first results indicated that
the investigated methodologies needed further development
and innovation in order to obtain satisfactory results.
The following aspects have been investigated: The parameter
estimation has focused mainly on a reliable estimation
of rudimentary variations of the fundamental
frequency and of the articulation parameters. After evaluation
of state-of-the-art methods, a novel method called
adaptive wavetable oscillator was developed; it provides a
good theoretical match to the revealed problems with
pathological voice excitation. This new method exhibits
reduced computational costs and provides similar performance
to state-of-the-art methods. For the estimation of
the articulation parameters, a method based on sub-space
projection was developed, but it led to unsatisfactory results.
Alternatively, a sub-band approach was developed,
which led to increased estimation results but requires a
dedicated method for the reconstruction of the speech
signal.