A subjective and objective evaluation of a codec for the electrical stimulation patterns of cochlear implants

Wireless transmission of audio from or to signal processors of cochlear implants (CIs) is used to improve speech understanding of CI users. This transmission requires wireless communication to exchange the necessary data. Because they are battery powered devices, energy consumption needs to be kept low in CIs, therefore making bitrate reduction of the audio signals necessary. Additionally, low latency is essential. Previously, a codec for the electrodograms of CIs, called the Electrocodec, was proposed. In this work, a subjective evaluation of the Electrocodec is presented, which investigates the impact of the codec on monaural speech performance. The Electrocodec is evaluated with respect to speech recognition and quality in ten CI users and compared to the Opus audio codec. Opus is a low latency and low bitrate audio codec that best met the CI requirements in terms of bandwidth, bitrate, and latency. Achieving equal speech recognition and quality as Opus, the Electrocodec achieves lower mean bitrates than Opus. Actual rates vary from 24.3 up to 53.5 kbit/s, depending on the codec settings. While Opus has a minimum algorithmic latency of 5 ms, the Electrocodec has an algorithmic latency of 0 ms.