P11 Speech in ‘Anti-Noise’: Intelligibility and listening-effort of shallow-envelope chimeras under active noise control headphones
Active noise control (ANC) headphones are known to alter human speech perception abilities in certain noises, such as from aircrafts or traffic. Despite being studied in diverse functional contexts (e.g. pain perception), ANC headphones’ impact into the human auditory system have not been thoroughly studied. Speech intelligibility under various listening conditions is known to depend on the temporal envelope fidelity of the sound producing device.
in this study, we investigated the effect of ANC on speech envelope perception. We propose a type of ‘chimera’, which is a parametrically degraded speech-like signal constructed by combining the envelope at shallow modulation depths. Stimuli are created from a popular speech dataset called Coordinate Response Measure. By measuring the variation in intelligibility and listening effort ratings (NASA task load index) of these chimera speech under ‘ANC on’ and ‘ANC off’ conditions of a commercially available headphone, we provide the first evidence of the interaction between noise cancellation and envelope of the speech signal. Using a repeated measures statistical test on logit transformed aggregate intelligibility scores, small but significant change in intelligibility is seen across the ANC conditions at most of the modulation depths. Similarly the listening effort ratings also show some interesting changes in the various dimensions (effort, frustration, etc.) across ANC conditions.
Overall, the effect of the ANC control system on the playback signal is unknown. Past studies involving ANC headphones and human participants have largely ignored the change in shape (i.e envelope) or other attributes of the signals reaching the listeners’ eardrum, and focused on end results alone. By systematically measuring the effect of ANC in a parametric degradation of the envelope, the present study opens up the investigation to a wider range of questions, starting with more specific changes to the envelope processing and also carrier (called “temporal fine structure”) processing by the human brain. Given the rising popularity of ANC headphones among users living in noisy metro cities around the world, this work sheds some light on the potential advantages of using an ANC headphone over and above the comfort aspect. It also serves as a possible improvement to the assessment protocols for device manufacturers, to design more human oriented noise cancelling algorithms.