Evaluating noise suppression methods for recovering the Lombard speech from vocal output in an external noise field

Speech production is affected by noise due to the Lombard effect. The traditional method of investigation is through headphone delivery of noise to allow speech to be recorded in quiet, but this could create an occlusion effect artefact during speech production. It is also not directly applicable when wearing hearing protectors, hearing aids, or other devices due to physical interference by the headphones. In these situations, the Lombard effect needs to be elicited by an external noise field and speech recorded in the presence of noise. This is a more challenging measurement situation, but one that preserves perception of own voice and the surrounding noise in interaction with the hearing device worn. Two methods, direct waveform subtraction and adaptive noise cancellation, were evaluated for suppressing the background noise in the recorded speech..The effects of sound recording configuration on performance was investigated for two microphone types (omnidirectional and directional) at two distances (50 and 25cm) in different noises and in the presence of real talker's movement. Results show that the amount of noise reduction with both suppression methods is greater for fluctuating than continuous noises. Overall, the best recording configuration for noise reduction was with the omnidirectional microphone at 25cm. Pitch extraction, energy level, and objective speech intelligibility and quality measures show that both suppression methods provide adequate noise reduction for SNRs as low as -10 dB, which is suitable to successfully recover Lombard speech produced in an external noise field with open ears and when wearing hearing protectors.