Enhancement of electrolaryngeal speech by adaptive filtering

Improving the Quality and Intelligibility of Electrolaryngeal Speech during Mobile Communication with Landline Analogous Bandpass Filtering

The normal functioning of the larynx or voicebox gives humans the ability to converse with others effortlessly. However, if the larynx is permanently removed due to injury or illness, speech cannot be produced. The electrolarynx, a noninvasive device used to produce speech for such persons, has a motor-induced hum which hinders telephone-based communication among electrolaryngeal speakers. This adversely affects the morale of electrolarynx users, leading to abandonment of technology, psychological issues and decreased quality of life. This paper examines a technique based on bandpass filtering of electrolaryngeal speech which has the potential of increasing the quality and intelligibility of speech produced by means of an electrolarynx. Finite impulse response and infinite impulse response filtering with bandpass frequencies analogous to telephone landline and wideband filtering were investigated. Objective testing and subjective testing of quality and intelligibility of electrolaryngeal speech have been performed in each phase of the work. Statistical analysis based on one-way analysis of variance (ANOVA) has been conducted after each round of subjective testing. Results indicate that the quality as well as intelligibility of electrolaryngeal speech can be improved with the help of bandpass filtering.

The influence of clear speech on auditory-perceptual judgments of electrolaryngeal speech

PURPOSE

To determine the influence of clear speech on auditory-perceptual judgments of speech acceptability and listener comfort for electrolaryngeal speech.

METHOD

Voice recordings were obtained from 10 electrolaryngeal speakers. Each speaker read the Rainbow Passage in two conditions: habitual speech and clear speech. Speakers were encouraged to speak as clearly as possible and over-articulate in the clear speech condition. Auditory-perceptual rating tasks were completed by 20 normal-hearing adults who evaluated 20 randomized voice recordings. Two counterbalanced listening sessions were used to gather ratings of speech acceptability and listener comfort.

RESULTS

A significant effect of speaking condition was found on listener judgments of speech acceptability, but not listener comfort. However, listener scores for speech acceptability and listener comfort were found to be significantly related. For all speakers, objective temporal measures indicated reduced speaking rates in the clear speech condition.

CONCLUSIONS

These findings suggest that volitional attempts to improve electrolaryngeal speech using clear speech might negatively impact listener judgments of speech acceptability, but not listener comfort. Further, the data suggest that speech acceptability and listener comfort might address unique perceptual entities. Overall, the strong relationship between these auditory-perceptual dimensions provide support for the use of scaled measurements to assess the impact of speech rehabilitation on individuals who use the electrolarynx.

The electrolarynx: voice restoration after total laryngectomy

The ability to speak and communicate with one’s voice is a unique human characteristic and is fundamental to many activities of daily living, such as talking on the phone and speaking to loved ones. When the larynx is removed during a total laryngectomy (TL), loss of voice can lead to a devastating decrease in a patient’s quality of life, and precipitate significant frustration over their inability to communicate with others effectively. Over the past 50 years there have been many advances in techniques of voice restoration after TL. Currently, there are three main methods of voice restoration: the electrolarynx, esophageal speech, and tracheoesophageal speech through a tracheoesophageal puncture (TEP) with voice prosthesis. Although TEP voice is the current gold standard for vocal rehabilitation, a significant minority of patients cannot use or obtain TEP speech for various reasons. As such, the electrolarynx is a viable and useful alternative for these patients. This article will focus on voice restoration using an electrolarynx with the following objectives: 1) To provide an understanding of the importance of voice restoration after total laryngectomy. 2) To discuss how the electrolarynx may be used to restore voice following total laryngectomy. 3) To outline some of the current electrolarynx devices available, including their mechanism of action and limitations. 4) To compare pros and cons of electrolaryngeal speech to TEP and esophageal speech.

3D simulation of an audible ultrasonic electrolarynx using difference waves

A total laryngectomy removes the vocal folds which are fundamental in forming voiced sounds that make speech possible. Although implanted prosthetics are commonly used in developed countries, simple handheld vibrating electrolarynxes are still common worldwide. These devices are easy to use but suffer from many drawbacks including dedication of a hand, mechanical sounding voice, and sound leakage. To address some of these drawbacks, we introduce a novel electrolarynx that uses vibro-acoustic interference of dual ultrasonic waves to generate an audible fundamental frequency. A 3D simulation of the principles of the device is presented in this paper.

Development and perceptual evaluation of amplitude-based F0 control in electrolarynx speech

PURPOSE

Current electrolarynx (EL) devices produce a mechanical speech quality that has been largely attributed to the lack of natural fundamental frequency (F0) variation. In order to improve the quality of EL speech, in the present study the authors aimed to develop and evaluate an automatic F0 control scheme, in which F0 was modulated based on variations in the root-mean-square (RMS) amplitude of the EL speech signal.

METHOD

Recordings of declarative sentences produced by 2 male participants before and after total laryngectomy were used to develop procedures for calculating F0 contours for EL speech. Specifically, the positive linear relationship between F0 and RMS amplitude observed in pre-laryngectomy speech was used as the basis for generating an F0 contour based on the amplitude variation of EL speech. An analysis-by-synthesis approach was used to modify the F0 contour, and a perceptual experiment was conducted to examine its impact on the quality of the EL speech.

RESULTS

The results of perceptual experiments showed that modulating the F0 of EL speech using a linear relationship between amplitude and frequency made it significantly more natural sounding than EL speech with constant F0.

CONCLUSIONS

The current study provides preliminary support for amplitude-based control of F0 in EL speech.

Fundamental frequency variation with an electrolarynx improves speech understanding: a case study

PURPOSE

This study examined the effect of fundamental frequency (F0) variation on the intelligibility of speech in an alaryngeal talker who used an electrolarynx (EL).

METHOD

One experienced alaryngeal talker produced variable F0 and a constant F0 with his EL as he read sentences aloud. As a control, a group of sentences with variable F0 was flattened at a constant F0. Twenty listeners heard these sentences in background noise and wrote down what they heard.

RESULTS

Speech understanding was on average 14% better with variable F0 controlled by the talker than the sentences produced with a constant F0 and the control sentences resynthesized with flattened F0.

CONCLUSIONS

Variable F0 contributes to speech understanding in noise. Because speech produced by an EL is considered to have poorer intelligibility in relation to other alaryngeal methods, training alaryngeal talkers to use variable F0 may prove to be of significant benefit for communication for those who use electrolarynges.

Electrolarynx in voice rehabilitation

OBJECTIVE

Patients of laryngeal cancer who have undergone the surgical removal of the entire larynx suffer the loss of phonation. Electrolarynx (EL) speech is the most commonly adopted alaryngeal phonation. However, EL speech is notorious of the sound quality being monotonic and robotic with the lack of pitch control and the presence of the radiated noise. This paper provides a review of modalities in EL speech as well as introducing the technologies to control the pitch and reduce the noise of the device.

METHODS

Improvements of EL speech quality have been divided into two parts: improving the sound quality of EL device by applying different enhancement algorithms to reduce the radiated and the additive noise, and implementing pitch-control function to the EL with advanced technology.

RESULTS

Adaptive filtering and the subtractive-type algorithms have shown to be able to reduce the noise level associated with EL speech. And more mature technologies are showing promise to the making of a hand-free EL system producing more accurate and synchronized pitch and voice onset control.

CONCLUSION

The advent of micro-technology and human-machine integration promisingly improves EL speech quality and more efficient algorithms enhance EL sound quality. Such improvements apparently improve the intelligibility of EL speech, and thus better quality of life of the EL speakers.

Application of spectral subtraction method on enhancement of electrolarynx speech

Although electrolarynx (EL) serves as an important method of phonation for the laryngectomees, the resulting speech is of poor intelligibility due to the presence of a steady background noise caused by the instrument, even worse in the case of additive noise. This paper investigates the problem of EL speech enhancement by taking into account the frequency-domain masking properties of the human auditory system. One approach is incorporating an auditory masking threshold (AMT) for parametric adaptation in a subtractive-type enhancement process. The other is the supplementary AMT (SAMT) algorithm, which applies a cross-correlation spectral subtraction (CCSS) approach as a post-processing scheme to enhancing EL speech dealt with the AMT method. The performance of these two algorithms was evaluated as compared to the power spectral subtraction (PSS) algorithm. The best performance of EL speech enhancement was associated with the SAMT algorithm, followed by the AMT algorithm and the PSS algorithm. Acoustic and perceptual analyses indicated that the AMT and SAMT algorithms achieved the better performances of noise reduction and the enhanced EL speech was more pleasant to human listeners as compared to the PSS algorithm.

Enhancement of electrolarynx speech based on auditory masking

Electrolarynx (EL) speech provides a valuable means of verbal communication for the laryngectomees. Yet EL speech tends to be less intelligible speech due to the presence of background noise. This paper addresses the issue of EL speech enhancement. The proposed approach takes into account the frequency-domain masking properties of the human auditory system for a subtractive-type enhancement process. Subtractive-type algorithms can efficiently reduce the radiated noise of EL speech but not to reduce the additive noise from the environment due to the use of fixed subtraction parameters. Considering the particular characteristics of EL speech, a new computationally efficient algorithm based on the perceptual weighting technique is developed to adapt the subtraction parameters. This leads to a significant reduction of the unnatural structure of the residual noise. Acoustic and perceptual experiments confirm that the enhanced EL speech is more pleasant to human listeners and the proposed algorithm results in improved performance over classical subtractive-type algorithms.

Aerodynamic characteristics of laryngectomees breathing quietly and speaking with the electrolarynx

The primary purpose of this study was to investigate the aerodynamic characteristics of laryngectomees under two conditions: breathing quietly and speaking with electrolarynx. Twenty male adult subjects, 8 normal speakers, and 12 laryngectomees participated the experiment. Airflow, pressure, and speech data were obtained simultaneously. The acceptability of electrolarynx speech under different conditions was also evaluated by 20 listeners (14 men, 6 women). Results indicated a higher peak expiration airflow and pressure among the laryngectomees as compared with the normal during breathing. Three different breathing patterns appeared among the laryngectomees when speaking with the electrolarynx: holding breath, exhaling, and breathing. Four long-time electrolarynx users held breath during speaking. Seven of 12 laryngectomees kept exhaling, whereas only 1 could breathe during speech production. In addition, (1) the acceptability of electrolarynx speech was the highest when speaking breathlessly; (2) no significant difference was found in the acceptability between the patterns of exhaling and breathing smoothly; and (3) the acceptability decreased if breathing quickly during phonation with the electrolarynx. It also suggests that the laryngectomees who can breathe during speaking may be more appropriate to use the new electrolarynx controlling the pitch by expiration pressure.

Impact of aberrant acoustic properties on the perception of sound quality in electrolarynx speech

A large percentage of patients who have undergone laryngectomy to treat advanced laryngeal cancer rely on an electrolarynx (EL) to communicate verbally. Although serviceable, EL speech is plagued by shortcomings in both sound quality and intelligibility. This study sought to better quantify the relative contributions of previously identified acoustic abnormalities to the perception of degraded quality in EL speech. Ten normal listeners evaluated the sound quality of EL speech tokens that had been acoustically enhanced by (a) increased low-frequency energy, (b) EL-noise reduction, and (c) fundamental frequency variation to mimic normal pitch intonation in relation to nonenhanced EL speech, normal speech, and normal monotonous speech (fundamental frequency variation removed). In comparing all possible combinations of token pairs, listeners were asked to identify which one of each pair sounded most like normal natural speech, and then to rate on a visual analog scale how different the chosen token was from normal speech. The results indicate that although EL speech can be most improved by removing the EL noise and providing proper pitch information, the resulting quality is still well below that of normal natural speech or even that of monotonous natural speech. This suggests that, in addition to the widely acknowledged acoustic abnormalities examined in this investigation, there are other attributes that contribute significantly to the unnatural quality of EL speech. Such additional factors need to be clearly identified and remedied before EL speech can be made to more closely approximate the sound quality of normal natural speech.

Enhancement of electrolarynx speech using adaptive noise cancelling based on independent component analysis

The electrolarynx provides a valuable means of verbal communication for people who cannot use their natural voice-production mechanism, but technology has changed very little since it was introduced in the 1950s. The presence of background noise degrades the resulting speech. In this study background noise was reduced by a new method, independent component analysis-based adaptive noise cancelling, which can remove noise components of the primary input signal based on statistical independence, by incorporating both second-order and higher-order statistics. The method shows better performance than the conventional least mean square algorithm. Acoustic analysis of the denoised electrolarynx speech revealed a significant reduction in the amount of background noise. Results from the perceptual evaluations indicated that the new filtering technique produced a noticeable improvement in the acceptability of the electrolarynx speech in a quiet environment (from 1.75 to 2.49, arbitrary units) or a noisy environment (from 0.59 to 1.82). In general, there was no significant improvement or degradation in intelligibility in the quiet environment (from 52.7 to 53.3). However, the processing did improve the intelligibility in a babble-noise environment (from 24.9 to 40.6). The improvement in acceptability and intelligibility may increase the communication ability of the user in daily situations.

Measuring the neck frequency response function of laryngectomy patients: implications for the design of electrolarynx devices

Measurements of the neck frequency response function (NFRF), defined as the ratio of the spectrum of the estimated volume velocity that excites the vocal tract to the spectrum of the acceleration delivered to the neck wall, were made at three different positions on the necks of nine laryngectomized subjects (five males and four females) and four normal laryngeal speakers (two males and two females). A minishaker driven by broadband noise provided excitation to the necks of subjects as they configured their vocal tracts to mimic the production of the vowels /a/, /ae/, and /I/. The sound pressure at the lips was measured with a microphone and an impedance head mounted on the shaker measured the acceleration. The neck wall passed low-frequency sound energy better than high-frequency sound energy, and thus the NFRF was accurately modeled as a low-pass filter. The NFRFs of the different subject groups (female laryngeal, male laryngeal speakers, laryngectomized males, and laryngectomized females) differed from each other in terms of corner frequency and gain, with both types of male subjects presenting NFRFs with larger overall gains. In addition, there was a notable amount of intersubject variability within groups. Because the NFRF is an estimate of how sound energy passes through the neck wall, these results should aid in the design of improved neck-type electrolarynx devices.

A comparison of two methods of formant frequency estimation for high-pitched voices

This study sought to compare formant frequencies estimated from natural phonation to those estimated using two methods of artificial laryngeal stimulation: (1) stimulation of the vocal tract using an artificial larynx placed on the neck and (2) stimulation of the vocal tract using an artificial larynx with an attached tube placed in the oral cavity. Twenty males between the ages of 18 and 45 performed the following three tasks on the vowels /a/ and /i/: (1) 4 seconds of sustained vowel, (2) 2 seconds of sustained vowel followed by 2 seconds of artificial phonation via a neck placement, and (3) 4 seconds of sustained vowel, the last two of which were accompanied by artificial phonation via an oral placement. Frequencies for formants 1-4 were measured for each task at second 1 and second 3 using linear predictive coding. These measures were compared across second 1 and second 3, as well as across all three tasks. Neither of the methods of artificial laryngeal stimulation tested in this study yielded formant frequency estimates that consistently agreed with those obtained from natural phonation for both vowels and all formants. However, when estimating mean formant frequency data for samples of large N, each of the methods agreed with mean estimations obtained from natural phonation for specific vowels and formants. The greatest agreement was found for a neck placement of the artificial larynx on the vowel /a/.