Understanding Lombard speech: a review of compensation techniques towards improving speech based recognition systems

The Lombard effect in children with cochlear implants: suprasegmental aspects

Children with cochlear implants (CI) communicate in noisy environments, such as in classrooms, where multiple talkers and reverberation are present. Speakers compensate for noise via the 'Lombard effect'. The present study examined the Lombard effect on the intensity and duration of stressed vowels in the speech of children with Cochlear Implants (CIs) as compared to children with Normal Hearing (NH), focusing on the effects of speech-shaped noise (SSN) and speech-shaped noise with reverberation (SSN+Reverberation). The sample consisted of 7 children with CIs and 7 children with NH, aged 7-12 years. Regarding intensity, a) children with CIs produced stressed vowels with an overall greater intensity across acoustic conditions as compared to NH peers, b) both groups increased their stressed vowel intensity for all vowels from Quiet to both noise conditions, and c) children with NH further increased their intensity when reverberation was added to SSN, esp. for the vowel/u/. Regarding duration, longer stressed vowels were produced by children with CIs as compared to NH in Quiet and SSN conditions but the effect was retained only for the vowels/i/,/o/and/u/when reverberation was added to noise. The SSN+Reverberation condition induced systematic lengthening in stressed vowels for children with NH. Furthermore, although greater intensity and duration ratios of stressed/unstressed syllables were observed for children with NH as compared to CIs in Quiet condition, they diminished with noise. The differences observed across groups have implications for speaking in classroom noise.

Vocal Behavior of Teachers Reading with Raised Voice in a Noisy Environment

(1) Objective: Teaching is a particularly voice-demanding occupation. Voice training provided during teachers’ education is often insufficient and thus teachers are at risk of developing voice disorders. Vocal demands during teaching are not only characterized by speaking for long durations but also by speaking in noisy environments. This provokes the so-called Lombard effect, which intuitively leads to an increase in voice intensity, pitch and phonation time in laboratory studies. However, this effect has not been thoroughly investigated in realistic teaching scenarios. (2) Methods: This study thus examined how 13 experienced, but vocally untrained, teachers behaved when reading in a noisy compared to quiet background environment. The quiet and noisy conditions were provided by a live audience either listening quietly or making noise by talking to each other. By using a portable voice accumulator, the fundamental frequency, sound pressure level of the voice and the noise as well as the phonation time were recorded in both conditions. (3) Results: The results showed that the teachers mainly responded according to the Lombard effect. In addition, analysis of phonation time revealed that they failed to increase inhalation time and appeared to lose articulation through the shortening of voiceless consonants in the noisy condition. (4) Conclusions: The teachers demonstrated vocally demanding behavior when speaking in the noisy condition, which can lead to vocal fatigue and cause dysphonia. The findings underline the necessity for specific voice training in teachers’ education, and the content of such training is discussed in light of the results.

Effects of task and language nativeness on the Lombard effect and on its onset and offset timing

This study focuses on the differences in speech sound pressure levels (here, called speech loudness) of Lombard speech (i.e., speech produced in the presence of an energetic masker) associated with different tasks and language nativeness. Vocalizations were produced by native speakers of Japanese with normal hearing and limited English proficiency while performing four tasks: dialog, a competitive game (both communicative), soliloquy, and text passage reading (noncommunicative). Relative to the native language (L1), larger loudness increments were observed in the game and text reading when performed in the second language (L2). Communicative tasks yielded louder vocalizations and larger increments of speech loudness than did noncommunicative tasks regardless of the spoken language. The period in which speakers increased their loudness after the onset of the masker was about fourfold longer than the time in which they decreased their loudness after the offset of the masker. Results suggest that when relying on acoustic signals, speakers use similar vocalization strategies in L1 and L2, and these depend on the complexity of the task, the need for accurate pronunciation, and the presence of a listener. Results also suggest that speakers use different strategies depending on the onset or offset of an energetic masker.