Subspace and envelope subtraction algorithms for noise reduction in cochlear implants

The performance of two noise reduction algorithms is evaluated using 14 subjects fitted with the Clarion S-Series and Clarion II implant devices. The first algorithm, based on signal subspace principles, is used for pre-processing sentences embedded in +5 dB noise. The second algorithm is based on the subtraction of the noisy speech envelopes from an estimate of the noise envelopes. The noise envelopes are estimated continuously using a variation of the minimum statistics algorithm. Results showed that the subspace algorithm produced significant improvements in sentence recognition scores compared to the subjects´ daily strategy. Small improvements were also obtained for a few subjects with the envelope subtraction algorithm.