A Psychoacoustic "NofM"-Type Speech Coding Strategy for Cochlear Implants

We describe a new signal processing technique for cochlear implants using a psychoacoustic-masking model. The technique is based on the principle of a so-called “NofM” strategy. These strategies stimulate fewer channels (N) per cycle than active electrodes (NofM;N < M). In “NofM” strategies such as ACE or SPEAK, only theN channels with higher amplitudes are stimulated. The new strategy is based on the ACE strategy but uses a psychoacoustic-masking model in order to determine the essential components of any given audio signal. This new strategy was tested on device users in an acute study, with either 4 or 8 channels stimulated per cycle. For the first condition (4 channels), the mean improvement over the ACE strategy was 17%. For the second condition (8 channels), no significant difference was found between the two strategies.