I have been focusing on human-machine interfaces the last month for an upcoming cover story in August. It has been a lot of fun rediscovering my passion for interface design, a passion I had put away in the closet for much too long. I have three things to share/ask you about regarding sound.

1) I would like to share an observation with you that until the last year I had never given much consideration to, and I wonder how many "normal" hearing people do. Many systems that I interact with use audio feedback, such as to let me know when I have pressed a button. An example would be my microwave or even the control panel at my gas station. What I have noticed is that many systems that use audio feedback seem to emit a single tone composed of a single frequency—my unscientific sample suggests it often is in the 1k+ Hz range. For normal hearing people with a normal hearing range, this is fine.

However, we have a large aging population, and a common type of hearing degradation this group of people is coping with is a loss of sensitivity at the higher end of the sound spectrum. Audio feedback based on a single frequency, with few or no harmonics in the generated tone can become the equivalent of no audio feedback for a growing portion of the population.

When designing a system that will implement audio feedback, consider using a chord with high, mid, and/or low frequencies in the beep. It might make sense to consider supporting more than a single tone and allowing the user to select from a range of tones. Or better yet, what does your design team do to accommodate people with hearing impairments so that they get the most value out of your products?

A hearing aid is no good for the type of hearing loss I have; however, I have recently heard about CROS (Contralateral Routing Of Signals) hearing aids that route a sound signal from one side of the head to the opposite side. As I understand it, most of the people (70%) who try these do not gain any value. Also, the remaining 30% that gain some value use these devices mostly on a part time basis (10% to 30% of the time). Do any of you have any experience with this type of hearing aid that you can share—privately or by posting your comments?

3) One topic that I did not get to spend enough time on while researching the August article was audio feedback and speech recognition; I hope to make that a topic for an article sometime next year. If you are working on such a project, or know someone who is, please let me know, I'd love to work with you for a future article, and maybe share some insights I have developed over the years because of my hearing impairment.