MIL Speech Seminar TRACHEOESOPHAGEAL SPEECH REPAIR Arantza del Pozo CUED Machine Intelligence Laboratory November 20th 2006

Arantza del CUED Machine Intelligence Laboratory 2 OUTLINE  Speech repair  Tracheoesophageal (TE) speech  Laryngectomy  Acoustic properties  Main limitations  Excitation repair  Previous attempts  Adopted approach  Baseline system  Enhanced system  Results  Duration repair  Preliminary experiments  Regression tree modelling  Improving TE recognition  Fixing recognition artifacts  Results  Conclusions and future work

Arantza del CUED Machine Intelligence Laboratory 3 OUTLINE  Speech repair  Tracheoesophageal (TE) speech  Laryngectomy  Acoustic properties  Main limitations  Excitation repair  Previous attempts  Adopted approach  Baseline system  Enhanced system  Results  Duration repair  Preliminary experiments  Regression tree modelling  Improving TE recognition  Fixing recognition artifacts  Results  Conclusions and future work

Arantza del CUED Machine Intelligence Laboratory 4 SPEECH REPAIR SPEECH REPAIR SYSTEM Speech Model Deviant features Correction algorithms

Arantza del CUED Machine Intelligence Laboratory 5 OUTLINE  Speech repair  Tracheoesophageal (TE) speech  Laryngectomy  Acoustic properties  Main limitations  Excitation repair  Previous attempts  Adopted approach  Baseline system  Enhanced system  Results  Duration repair  Preliminary experiments  Regression tree modelling  Improving TE recognition  Fixing recognition artifacts  Results  Conclusions and future work

Arantza del CUED Machine Intelligence Laboratory 6 Laryngectomy  Laryngectomy is a surgical procedure which involves the removal of the larynx, i.e. vocal cords, epiglottis and tracheal rings  Speech rehabilitation after laryngectomy  Esophageal speech  TE speech  Electrolaryngeal speech  TE speech is the most frequently used voice restoration technique after laryngectomy

Arantza del CUED Machine Intelligence Laboratory 7 Acoustic properties of TE speech  Voicing source highly variable and deviant  Lower F0 (female) and higher jitter and shimmer  Higher high-frequency noise and lower harmonic-to- noise-ratio (HNR), glottal-to-noise excitation ratio (GNE), band-energy difference (BED)  Some evidence of higher formant values in Spanish and Dutch TE speech  Shorter maximum phonation time, longer vowel duration and slower speaking rates

Arantza del CUED Machine Intelligence Laboratory 8 Main limitations of TE speech  Inability to properly control the EXCITATION  deviant glottal waveforms  irregular pitch and amplitude contours  higher turbulence noise  spectral envelope deviations caused by coupling  DURATION deviations caused by the disconnection between the lungs and the vocal tract  more pauses  longer vowels  slower rates  rushes before breaks

Arantza del CUED Machine Intelligence Laboratory 9 OUTLINE  Speech repair  Tracheoesophageal (TE) speech  Laryngectomy  Acoustic properties  Main limitations  Excitation repair  Previous attempts  Adopted approach  Baseline system  Enhanced system  Results  Duration repair  Preliminary experiments  Regression tree modelling  Improving TE recognition  Fixing recognition artifacts  Results  Conclusions and future work

Arantza del CUED Machine Intelligence Laboratory 10 Previous excitation repair attempts  Qi et al.  Resynthesis of female TE words with a synthetic glottal waveform and with smoothed and raised F0  Replacement of voice source and conversion of spectral envelopes  Limitations of previous repair attempts  Only most obvious deviant features have been tackled  Evaluation limited to sustained vowels and words  Only a small number of TE speakers and qualities have been tested  Degree of perceptual enhancement has not been quantified

Arantza del CUED Machine Intelligence Laboratory 11 Adopted approach  DATA  13 TE speakers (11 male, 2 female)  Patients of the Speech and Language Therapy Department of Addenbrookes Hospital, Cambridge  Control group of 11 normal speakers (8 male, 3 female)  BASELINE SYSTEM  Glottal resynthesis  Jitter and shimmer reduction  ENHANCED SYSTEM  Spectral envelope smoothing and Tilt reduction Feature correction Perceptual evaluation DEVIANT FEATURES: -voice source -jitter & shimmer -spectral envelope

Arantza del CUED Machine Intelligence Laboratory 12 Baseline system  Glottal resynthesis  breathiness reduction  Jitter and shimmer reduction  roughness reduction Lip radiation VT

Arantza del CUED Machine Intelligence Laboratory 13 Enhanced system (1/2)  Resynthesised speech still has a harsh quality caused by deviations in TE spectral envelopes (SE)  Spectral envelope analysis  Higher std of formant gains, frequencies and bandwidths and spectral distortion  Lower relative gain difference between 1st and 3rd formants and spectral tilt

Arantza del CUED Machine Intelligence Laboratory 14 Enhanced system (2/2)  Enhancement algorithm  To reduce differences between estimated consecutive SE  LSF median smoothing  To decrease spectral tilt  Low-pass filtering

Arantza del CUED Machine Intelligence Laboratory 15 Results  Perceptual tests originalbaselineenhanced “more breathy” 82.69%17.31% “ harsher ” 73.72%26.28% “more normal speaker” 58.33%41.67% 38.78%61.22%

Arantza del CUED Machine Intelligence Laboratory 16 OUTLINE  Speech repair  Tracheoesophageal (TE) speech  Laryngectomy  Acoustic properties  Main limitations  Excitation repair  Previous attempts  Adopted approach  Baseline system  Enhanced system  Results  Duration repair  Preliminary experiments  Regression tree modelling  Improving TE recognition  Fixing recognition artifacts  Results  Conclusions and future work

Arantza del CUED Machine Intelligence Laboratory 17 Preliminary experiments  Duration deviations  more pauses  longer vowels  slower rates  rushes before breaks  Possible duration repair approaches  Rule-based  Reduce pauses, reduce vowels, increase speech rate, increase duration of phones before breaks, etc. Difficult to obtain adequate reduction/increase rates Break sentence rhythm  Transplantation of average normal phone durations  Phone durations obtained with Forced Alignment (FA) Overall improvement which increased naturalness of TE sentences Sentence rhythm was preserved  Duration repair algorithm is an automatization of the transplantation experiment

Arantza del CUED Machine Intelligence Laboratory 18 Regression tree modelling (1/2)  Classification and regression trees (CART) are widely used for duration modelling in TTS systems  Employed features are extracted from text  Phone identity  Identities of previous and next phones  Position of syllable in word  Position of word in sentence  Number of syllables before/after a break  Type of lexical stress  Lexical stress type of previous and next syllables ...  A speech repair framework constrains the possible feature space to recognisable features  For TE speech repair, assumed that only phone recognition is viable  Features relying on word, syllable or lexical stress information cannot be used

Arantza del CUED Machine Intelligence Laboratory 19 Regression tree modelling (2/2)  Several CART trees were built with different features  Explored features  Phone identity  Identities of previous and next phones  Positions of phones in the sentence  Pitch and energy (as an attempt to incorporate some stress info)  Short pauses (SP) not regarded as phones, modelled independently  Trees  T1  F1: phone identity  T2  F2: F1 + previous & next phone identities (broad class)  T3  F3: F2+ position of phone in sentence  T4  F4: F3+ pitch (positive/negative/no slope)  T5  F5: F4+ energy (positive/negative/no slope)  TSP  number of phones since previous sp & until next sp  Performance measured as Mean Squared Error (MSE) between normal mean durations used for transplantation and predicted values  T3>T2>T1>T5>T4  Substitution of T3+TSP predicted durations of TE sentences with FA phone segmentation almost indistinguishable from transplantation

Arantza del CUED Machine Intelligence Laboratory 20 Improving TE recognition (1/2)  Little work on automatic TE speech recognition  Haderlein et al. (2004) adapted a speech recogniser trained on normal speech to single TE speakers by unsupervised HMM interpolation and obtained an average word accuracy of 36.4%  Focus on improving TE phone recognition  Novel performance measures which take recognition (r), segmentation (s) and duration prediction (p) errors into account FA REC

Arantza del CUED Machine Intelligence Laboratory 21 Improving TE recognition (2/2)  Explored systems  Baseline (BL): monophone HMM trained on WSJCAM0  R1: BL + CMN + CMLLR  R2: R1 + MAP  R3: R1 + bigram LM  R4: R1 + trigram LM  R5: CUHTK 2003 BN LVCSR + CMLLR  phone level output  Results  R5>R4>R3>R1>R2 BLR1R2R3R4R5 SPC [%] SPE [ms]

Arantza del CUED Machine Intelligence Laboratory 22 Fixing recognition artifacts  Use of best recognised labels for duration repair still produced artifacts  Method for robust duration modification (RM)  Take recognition confidence into account  computed from  TE phone duration probability distributions  recogniser confidence scores  takes phone confusions into account in R4

Arantza del CUED Machine Intelligence Laboratory 23 Results  Objective evaluation: MSE between repaired sentences and target transplanted durations  R5+RM>R5>R4+RM>R4>original TE durations  Subjective evaluation: perceptual test RANK (1-5) OTR PREFERENCE TEST R4 48% R5 52% ->=< T - M M - O T - O

Arantza del CUED Machine Intelligence Laboratory 24 OUTLINE  Speech repair  Tracheoesophageal (TE) speech  Laryngectomy  Acoustic properties  Main limitations  Excitation repair  Previous attempts  Adopted approach  Baseline system  Enhanced system  Results  Duration repair  Preliminary experiments  Regression tree modelling  Improving TE recognition  Fixing recognition artifacts  Results  Conclusions and future work

Arantza del CUED Machine Intelligence Laboratory 25 CONCLUSIONS AND FUTURE WORK  Deviant TE excitation and duration features have been identified and repaired  Synthetic quality of excitation repaired speech nullifies results in some cases  Future work  Improve excitation resynthesis quality  Improve TE speech recognition step  Attempt text-based features for duration modelling