O. Dyrlund et al., DIGITAL FEEDBACK SUPPRESSION (DFS) - CHARACTERIZATION OF FEEDBACK-MARGIN IMPROVEMENTS IN A DFS HEARING INSTRUMENT, Scandinavian audiology, 23(2), 1994, pp. 135-138
The introduction of a new power behind-the-ear hearing instrument equi
pped with an integrated digital feedback suppression (DFS) system, bas
ed on adaptive, digital signal processing, creates the need for new me
thods for evaluating the characteristics of this new technology. A spe
cial measuring method based on determination of the complex loop gain
of the DFS instrument and the associated feedback path is described. T
his method yields information about the static feedback-margin improve
ment due to the DFS system, and the method is usable especially in con
nection with measurements on real ears. It requires fairly advanced te
st facilities, including a dual-channel FFT analyzer and, by preferenc
e, an anechoic room. Loop gain measurements on the new DFS power behin
d-the-ear hearing instrument show encouraging results. Groups of profo
undly hearing-impaired children and adults were tested, and static fee
dback-margin improvements in the order of 10 dB for the new DFS power
hearing instrument were seen. Variations were largest for groups using
own ear moulds and individually fitted instruments.