Audio Privacy: Reducing Speech Intelligibility while Preserving Environmental Sounds

Abstract

Audio monitoring has many applications but also raises pri-
vacy concerns. In an attempt to help alleviate these con-
cerns, we have developed a method for reducing the intelli-
gibility of speech while preserving intonation and the ability to recognize most environmental sounds. The method is based on identifying vocalic regions and replacing the vocal tract transfer function of these regions with the transfer function from prerecorded vowels, where the identity of the replacement vowel is independent of the identity of the spoken syllable. The audio signal is then re-synthesized using the original pitch and energy, but with the modi ed vocal tract transfer function. We performed an intelligibility study which showed that environmental sounds remained recognizable but speech intelligibility can be dramatically reduced to a 7% word recognition rate.