Embedded Processing

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?

2) This issue rudely came to my attention when I realized that I could no longer hear my alarm clock with one of my ears, regardless of whether I'm awake or asleep. To put this in context, I have one normal ear while the other ear is practically deaf (and definitely useless for distinguishing human speech and detecting a growing list of other sounds).

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.