Input Dynamic Range (IDR)

Input Dynamic Range (IDR), or "Sound Window," is one of the least known and understood cochlear implant features--but one of its most important as well.  IDR is basically the range of sound that the processor captures and sends to the implant to hear with.  Sounds that are louder than the implant's Input Dynamic Range are compressed and distorted, while those too soft for it are simply discarded and never heard.

Using a sensitivity control found on all implants, the Input Dynamic Range can be raised or lowered to capture softer or louder sounds respectively; however, doing so involves trading off hearing loud sounds so that softer ones can be heard, and vice versa.  The overall size of this “sound window” remains fixed by the limitations of the hardware.  

Speech can fluctuate over a range of 50 decibels, so it is critical than a cochlear implant system capture a wide range of the sound signal.   Specifically, a significant amount of research studies have shown that a wider IDR may (a) provide for a more accurate and full representation of sound, (b) minimize the need to adjust the sensitivity controls for different listening environments, (c) enable better understanding of soft sounds, and (d) improve language development in young children who benefit from “incidental listening” of speech that may not be directed at them.  Studies supporting these claims are as follows:

• Shannon, R.V., R.S. Tyler (1993). Psychophysics. (ed). Cochlear Implants: Audiological foundations, pp. 357-388.

• Zeng, F.G., Galvin, J.J. (1999). Amplitude mapping and phenome recognition in cochlear implant listeners. Ear and Hearing, 20 (I), 60-74.

• Donaldson, G.S. & Smith, S.L. (University of Minnesota). Poster presentation, American Academy of Audiology, 1999.

• Skinner, M.W., et. al., (1997). Speech recognition at stimulated soft, conversational, and raised-to-loud vocal efforts by adults with cochlear implants. Journal of the Acoustical Society of America, 101(6), 3766-3782.

• Zeng, F.G., & Shannon, R.V. (1997). Loudness of simple and complex stimuli in electric hearing. Annals of Otology, Rhinology & Laryngology, Suppl. 166, 235-238.

Critics argue that a wide IDR simply lets in too much background noise and can make it more difficult to hear speech.  However, there does not appear to be much evidence supporting this argument, and implant recipients do have the option of reducing their IDR if they desire (which not many do, given the choice).  Different implants have different sizes of Input Dynamic Range, so it may be an additional factor worth considering.  The Clarion has the largest IDR, followed by Med-El, and trailed by the Nucleus.