Biomedical subjects

O Dyrlund

Publications and source records attributed to O Dyrlund.

6 recordsLinked to original sources

PubMed1992

Coherence measurements in hearing instruments, using different broad-band signals.

In this investigation the effect of different broad-band test signals on non-linear distortion in hearing instruments was examined using coherence measurements, and the interaction between different test signals and types of automatic signal processing is explored. It is concluded that the use of coherence measurements to quantify non-linear distortion in hearing instruments is only valid for instruments without automatic signal processing. This limitation arises because interaction between type of test signal and the automatic signal processing used causes system time-variations, which influences the measured coherence function in an uncontrollable way.

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↗

PubMed1990

Gain and feedback problems when fitting behind-the-ear hearing aids to profoundly hearing-impaired children.

Previous laboratory studies with severely and profoundly hearing-impaired persons aided with behind-the-ear (BTE) hearing aids have resulted in prediction rules for insertion gain and maximum gain without occurrence of acoustic feedback. The practicability of these findings was investigated in the present field trial with 21 profoundly deaf children fitted with power BTE hearing aids. In dialogue situations without background noise, the gain control settings were in accordance with the insertion gain prediction rule, whereas preferred gain may be 10 dB lower in the presence of noise. Consistent with the prediction rule for maximum gain without feedback and the gain response of the present test hearing aid, we observed oscillation in the high-frequency range in which the children had no remaining hearing. When the high-frequency gain was reduced, sufficient low-frequency gain could be provided without feedback problems.

Acoustics↗

PubMed1989

Acoustical feedback associated with the use of post aural hearing aids for profoundly deaf children.

The feedback properties of 29 ears fitted with post aural hearing aids and hard acrylic earmoulds, have been investigated for a group of profoundly deaf children. Complex loop gain has been measured, and maximum hearing aid gain before instability has been calculated from the measurement results. Guidelines for prediction of maximum hearing loss, which can be managed, are stated, and a suitable hearing aid frequency response for profoundly deaf children is proposed. This response ensures that acoustical feedback above approximately 1 kHz does not limit the low frequency gain, which is assumed to be very important for the speech recognition.

Acoustics↗

PubMed1989

Characterization of non-linear distortion in hearing aids using coherence analysis. A pilot study.

Coherence is a frequency-domain measure of linear dependence between input and output of a system, e.g. a hearing aid, and describes the cumulative effect of different forms of signal corruption, e.g. noise and non-linear distortion. From the coherence function, a general frequency-dependent signal-to-noise ratio can be derived. In this investigation, the applicability of this measuring technique is demonstrated in connection with non-linear distortion in hearing aids. The influence of hearing aid gain and automatic gain control is illustrated, with speech-shaped noise as input signal. For the three hearing aids tested. The gain setting influences the signal-to-noise ratio heavily due to non-linear distortion, especially near maximum gain. The introduction of automatic gain control reduces the effect of non-linear distortion somewhat at high gain settings.

Hearing Aids↗

PubMed1988

Some relationships between hearing aid frequency response and speech discrimination of profoundly deaf children. Pilot study.

A significant improvement in auditory-visual speech discrimination has been established for a group of profoundly deaf children with hearing losses in the range from 85 to 120 dB HL (pure tone average (500, 1,000, 2,000 Hz] by increasing the low frequency hearing aid gain by approximately 10 dB and reducing the high frequency gain by approximately the same magnitude. The improvements were concentrated in the hearing loss range from 95 to 115 dB HL. A tendency for improvement in auditory discrimination was indicated as well.

Adolescent↗