Voiced speech from whispers for post-laryngectomised patients

Patients who suffer larynx and voice box deficiencies are typically unable to speak anything more than hoarse whispers without the aid of voice prostheses or rehabilitation techniques such as oesophageal speech. Speech therapists and researchers working in this field have, for many years, pursued the goal of rehabilitation of such patients so as to return to them the ability to speak in a natural sounding voice. Typically due to removal of, or damage to, the voice box in a surgical operation such as laryngectomy, the pitch generation mechanism within these patients voice production systems, is lacking. Without a source of excitation for voiced speech, only hoarse, whisper like and sometimes not easily perceptible sounds can be produced. This speech is obviously different to that from normal speakers, and will have lost many of the distinctive characteristics of the original speech. However, these patients typically retain the ability to whisper in a similar way to normal speakers. This paper aims to present an engineering approach to providing laryngectomy patients the capacity to regain their ability to speak with a more natural voice, and incidentally to allow them to conveniently use a mobile telephone for communication. The non-invasive and non-surgical techniques discussed use auditory information coupled with signal analysis, formant insertion and smoothing and spectrum enhancement within the reconstruction process. With these techniques, natural sounding speech is obtained from spoken whisper-speech building upon an analysis-by-synthesis system for vocal reconstruction with a modified CELP codec.