These audio samples are based on the results of several studies with MED-EL recipients.^1,2,3,4 The science behind these sound samples is complex, but read on if you'd like an in-depth explanation and want to learn more about how we created these audio simulations.

Our Triformance audio tool is not meant to approximate hearing with a cochlear implant system, but rather, to demonstrate the effects of pitch mismatch on sound quality and how that mismatch can be reduced by Triformance.

In natural hearing, sounds are detected along the whole cochlea. The base of the cochlea (basal region) detects high-pitched sounds, while the tip of the cochlea (apical region) detects low-pitched sounds.
A cochlear implant electrode array that is too short to reach the apical region of the cochlea can create a place-pitch mismatch and a distorted perception of sound.  This means that a low-pitched sound will sound unnaturally high-pitched. An electrode array that is long enough to extend into the apical region can provide a better pitch match, but will still need to employ variable-rate sound coding to ensure the best possible pitch match.^1,2,3

In a 2014 study by Prentiss et al., a MED-EL recipient with preserved residual hearing was able to compare the pitch of stimulation through a cochlear implant to the pitch of tones as heard through residual acoustic hearing.⁴ This study demonstrates that using a short electrode and fixed-rate only sound coding can create a pitch-mismatch.
The recipient had a full-length MED-EL electrode array designed for Complete Cochlear Coverage, so pitch perception could be tested on individual electrode contacts along the whole cochlea.

From these results, we can infer that:

When using a short (18-20 mm long) electrode array in combination with fixed-rate sound coding, a 100 Hz tone presented through the cochlear implant system will sound unnaturally high at a pitch of 850 Hz. To demonstrate the effect of this pitch mismatch with a short electrode array and fixed-rate stimulation, all the frequencies of sound in the first sound sample were shifted to 850 Hz and above.

When using a long electrode that provides Complete Cochlear Coverage and fixed-rate sound coding, then the 100 Hz tone will sound less unnaturally high at a pitch of 400 Hz. To demonstrate the effect of this pitch mismatch with a full-length electrode array and fixed-rate only stimulation, all the frequencies of sound in the second sound sample were shifted to 400 Hz and above.

When combining both Complete Cochlear Coverage and variable-rate FineHearing sound coding, then the 100 Hz tone can be heard as nearly natural at a pitch of 150 Hz. To demonstrate the effect of pitch matching with a full-length electrode array and variable-rate stimulation, all the frequencies of sound in the third sound sample were shifted to 150 Hz and above.