HearLoss - Hearing Loss Demonstrator

HearLoss is an interactive Windows PC program for demonstrating to normally hearing people the effects of hearing loss. With HearLoss you can replay speech, music and noise under a variety of loudness, filtering and masking conditions typical of hearing impairments. Best of all you can interactively change the settings and demonstrate their consequences.

Description

The HearLoss program plays back pre-recorded audio samples of some speech, some music and some typical background noise, either singly or in combination. As it replays, three sliders control a simulation of the effects of three common consequences of hearing loss: loss in amplitude sensitivity, reduction in frequency range, and loss in spectral detail. Changes in the amplitude sensitivity slider changes the loudness of the sound, changes to the frequency range slider changes the upper frequency limit of the sound, while changes to the spectral detail slider changes the amount of fine structure present in the spectrum.

Download & Installation

The program is only available for Windows PCs by anonymous FTP from

To download the full installation, right click on the link above and choose "Save Target As". Save the file to your desktop or to a folder on your computer. Then run the file to install the program and to add an entry to your Start Programs menu. Once installed you can delete the downloaded file.

The full installation comes with three short audio samples in these files:

• speech.wav - sample of speech signal
• music.wav - sample of music signal
• noise.wav - sample of noise signal

You can replace these with audio samples of your own. To make the audio files compatible with HearLoss, ensure that the files are saved with the format: "PCM 44.1kHz 16-bit Mono". The Windows Sound Recorder application can convert WAV files between formats.

To download the program alone, right click on the second link above and choose "Save Target As". Save the file to a new folder on your computer. You will then need to provide your own sound files as described above and put them in the same folder as the program.

Suggestions for Use

This is one way you might use the program to demonstrate the effects of hearing loss to normally-hearing people:

1. Start the music playing and adjust levels so that the audience can hear it clearly. Stop the music.
2. Explain that deafness is not just all or nothing, but that hearing impairments come in various degrees.
3. Play music and demonstrate loss in amplitude sensitivity to mild, moderate and severe losses.
4. Repeat for speech. Point out that difficulty in hearing speech affects our social interactions - we can't follow what is going on in a group conversation, for example.
5. Explain that if hearing loss was just a loss in sensitivity, then we could restore peoples' hearing with just an amplifier.
6. Explain that most hearing loss is not just a drop in quantity but also a dop in the quality of sound perceived. In particular the kind of hearing impairment asoociated with old age has associated changes in frequency range and spectral detail.
7. Play music and demonstrate what a reduction in frequency range means: at mild, moderate and severe levels.
8. Repeat for speech. Point out that even if the speech were loud enough, the loss of high frequencies makes it harder to understand.
9. Play music and demonstrate the consequences of a loss in spectral detail. The effect of this slider is like looking at an out-of-focus photograph - you can't see all the fine detail. Get the audience to listen as you bring the slider back to normal - you should hear the signal getting "clearer".
10. Play speech and noise simultaneously with sliders set to normal. Point out that the speech is still fairly easy to understand.
11. Add a moderate loss of frequency range and spectral detail. The speech is pretty unintelligible now, although it becomes a bit clearer when the noise is turned off. Hearing impaired people find listening in conditions of noise far more difficult than normally hearing people.

Technical details

The three audio files are loaded into memory and scaled so that they can not overload the output when added together. When replay starts, the combined audio is processed in the frequency domain to remove frequency components above some limit set by the frequency range slider, and to smear energy across frequency according to the setting of the frequency selectivity slider. The spectral smearing is based on the technique described by Baer & Moore (1993). Amplitude sensitivity is changed partly through the Windows audio mixer volume control and partly by scaling the signal.

The graphic equaliser display is based on a number of auditory filter sized channels, each 1 bark wide. The graphic equaliser has a simple damping mechanism to reduce fine temporal fluctuations.

Approximate parameter settings for the sliders areas follows:

The bark scale is a measure of auditory filter width. When the frequency selectivity control is set to one bark then sound components that fall within one bark of one another interfere and so cannot be easily distinguished as separate elements of the sound. By definition, normal hearing has a frequency selectivity of one bark, so the program does not need to do any additional frequency smearing for the normal setting.

This program may not run correctly on PCs with a low processor speed which are unable to perform the frequency analysis and synthesis in real time. A processor speed of 1GHz or greater is recommended.

References

• Thomas Baer & Brian Moore, "Effects of spectral smearing on the intelligibility of sentences in noise", The Journal of the Acoustical Society of America -- September 1993 -- Volume 94, Issue 3, pp. 1229-1241.

Bug reports

Please send suggestions for improvements and reports of program faults to SFS@phon.ucl.ac.uk.

Please note that we are unable to provide help with the use of this program.

Copyright

HearLoss is not public domain software, its intellectual property is owned by Mark Huckvale, University College London. However HearLoss may be used and copied without charge as long as the program remains unmodified and continues to carry this copyright notice. Please contact the author for other licensing arrangements. HearLoss carries no warranty of any kind, you use it at your own risk.