As far as my understanding of hearing aids go there are two
brands of hearing aids that have different compression
bands for different frequencies. Both the Multi Focus by
Oticon and Resound Hearing Aids divide the signal into
two separate bands, usually a high frequency band and a low
frequency band. Also for each there are varying amounts
of compression depending on the level of the input. For example
signals at a higher intensity may have more gain whereas signals
at a lower frequency will have more gain. These compression ratios
can be different for either frequency band. Also the crossover frequency
(Frequency that divides the two bands) can be varied. This is programmed
into the aid by a computer for the Resound and is done by trimpot
adjustments on the Multi Focus. This Multiband Dynamic Range Compression
is based upon research that has shown that persons with hearing impairment
have a different loudness growth function than those with normal hearing.
As far as the 22 channel cochlear implant goes (and I a not the expert on
this) the 22 channels represent 22 electrodes that are implanted into
the cochlea that may or may not be used based on myriad of factors (if
the arrangement is all the way in the cochlea, if the patient will tolerate
the firing of all the electrodes, etc). The signal that is picked up
by a post aricular microphone is sent to a speech processor which codes
the information based on a coding strategy and sends the signal to the
cochlear inplant whose active electrodes "fire" accordingly and stimulate
the nerve. The coding strategies get to be fairly complex and I do not
understand them fully, some are based on F0 F1 F2 F3, bands, etc. if you want
more info on coding strategies it would be best to hear from an audiologist
on a cochlear implant team or from manufacturers who make the implants.
Thank you for your support,
Paul dybala
dybala at callier.utdallas.edu
