Knowledge of the frequency resolving power of the pathological ear can
be helpful for good hearing-aid prescription. In particular, the slop
e of the low-frequency edge of the auditory filter will determine the
extent of upward spread of masking. The most precise method for measur
ing this filter is the ''notched-noise'' procedure developed in the ea
rly 1980s. However, at this moment, the notched-noise protocol is too
time consuming for clinical use. In this paper we developed a protocol
that is applicable in the clinic. In the first part of the study we i
nvestigated the minimum number of threshold measurements necessary for
a reliable estimation of the filter parameters. For this purpose we a
nalyzed 99 filters originally obtained with 13 threshold measurements.
The influence of reducing the number of notch widths used to obtain f
ilter shapes on the variability of filter parameters was investigated.
Subsets of seven and five notch widths gave about the same standard d
eviations of the differences between the parameters obtained with the
subset and the parameters obtained with the full set of 13 thresholds,
while subsets of four and three notch widths gave significantly highe
r variability. However, because small deviations of one threshold dete
rmination can give rise to a large change in filter parameters, especi
ally for filters with flatter skirts, it is strongly recommended to re
duce the variability by measuring thresholds twice (test and retest).
In the second part of the study we investigated a faster method for me
asuring thresholds. The forced-choice paradigm normally used in notche
d-noise procedures was replaced by a Bekesy paradigm. The Bekesy parad
igm did not significantly increase intra-individual standard deviation
s, but did reduce the measuring time by more than 50%. In conclusion,
the new procedures reduce the measurement time needed to obtain reliab
le estimates of auditory-filter parameters by a factor of about 5. The
new protocol lasts about 15 min for each filter measurement, which ap
pears to be acceptable for clinical use, at least for difficult-to-fit
hearing aid users.