Biomedical subjects

N Bisgaard

Publications and source records attributed to N Bisgaard.

4 recordsLinked to original sources

PubMed2001

The European experience.

This article presents an overview of past and current experiences with time division multiple assess-based (Global System for Mobil Communication) mobile telephones in Europe as seen by the European Hearing Instrument Manufacturers Association. Initial fear of widespread interference problems for hearing aid users in general owing to use of a new generation of mobile telephones seems unjustified. The background for the International Electrotechnical Commission 118-13 standard for measuring interference is described. No solution to complete elimination of interference problems resulting from direct contact between hearing aids and mobile telephones has yet been found. Several reports on the subjects are cited, and new work on measurement standards for near-field situations is mentioned.

Electromagnetic Phenomena↗

PubMed1994

Digital feedback suppression (DFS). Clinical experiences when fitting a DFS hearing instrument on children.

A new power behind-the-ear hearing instrument with digital feedback suppression (DFS) seems to be an important step towards solving the problems of acoustic feedback in high power instrument fittings. Previous experiences (Dyrlund & Bisgaard, 1991) with a DFS prototype are confirmed in the present work. Ten profoundly hearing-impaired children were fitted with the new DFS instrument and wore it over a trial period of approximately three weeks. with the new instruments the rationale was to supply equivalent low frequency (< 1 kHz) gain compared to the subjects' original hearing instruments, and extra 5-10 dB high frequency (> 1 kHz) gain. The hypothesis was that with the new DFS system it would be possible to provide extra high frequency gain for these children without the annoyance of acoustic feedback. The test included questionnaires before and after the trial period, comparative free-field audiometry between the subjects' original and DFS instruments. The free-field audiometric results show a typical improvement of 5-10 dB at 2000 Hz and even larger improvements at higher frequencies. The increased high frequency gain provided by the new instruments did not give rise to significant complaints of feedback or howling during the trial period, and was generally preferred by 9 of the 10 subjects after the trial period.

Adolescent↗

PubMed1994

Digital feedback suppression (DFS). Characterization of feedback-margin improvements in a DFS hearing instrument.

The introduction of a new power behind-the-ear hearing instrument equipped with an integrated digital feedback suppression (DFS) system, based on adaptive, digital signal processing, creates the need for new methods for evaluating the characteristics of this new technology. A special measuring method based on determination of the complex loop gain of the DFS instrument and the associated feedback path is described. This method yields information about the static feedback-margin improvement due to the DFS system, and the method is usable especially in connection with measurements on real ears. It requires fairly advanced test facilities, including a dual-channel FFT analyzer and, by preference, an anechoic room. Loop gain measurements on the new DFS power behind-the-ear hearing instrument show encouraging results. Groups of profoundly hearing-impaired children and adults were tested, and static feedback-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.

Acoustic Stimulation↗

PubMed1991

Acoustic feedback margin improvements in hearing instruments using a prototype DFS (digital feedback suppression) system.

The properties of a prototype DFS (digital feedback suppression) system have been investigated. 21 ears fitted with behind-the-ear (BTE) hearing instruments and hard acrylic ear-moulds and 4 ears fitted with vented in-the-ear (ITE) hearing instruments were selected for the investigation. Two ITE instruments with different venting were employed to one of the ears. Complex loop gain has been measured in an anechoic room, and from these measurements the improvements in acoustic feedback margin due to the DFS system have been determined. For the BTE group, median values of 13.1 and 10.0 dB of improvement were established for two sets of measurements introducing a 180 degrees phase shift in connection with the last set of measurements. For the ITE group, values from 9.8 to 16.1 dB and from 13.7 to 16.3 dB of improvement were observed for the normal and the 180 degrees phase shift conditions respectively. Beyond this the DFS system may improve the sound quality to some extent, because the amplitude distortion, caused by the external feedback signal, is almost completely eliminated.

Acoustic Stimulation↗