People are not very good at distinguishing the pitch of two sounds, unless they hear them close together. My Casio watch makes good use of a fairly subtle change in tone. The watch has several modes: normal time, stopwatch, set alarm and dual time. The mode button changes from one to another. When I am finished using a mode, I can press the mode button to leave that mode, but I have to visit each of the remaining modes before I get back to normal mode. At first I found this a bit frustrating. The number of button presses required to get back to normal mode varied depending on what mode I was leaving. If I had just used the stopwatch, I iterate through set alarm and dual time to ge to normal mode, so that took three presses, but if I was just using dual time it would only take one press to get to normal mode. Of course one press too many means that you have to iterate through the whole list again.
Then I noticed that the tone of the key beep when entering normal mode was slightly different than the key beep when entering any other mode. The interface designer was giving me an easy way to know when I had reached the end of the list. So now, rather than watching each mode appear on the display, I press the button quite quickly and listen for the button beep to change.
I have used other devices that have different tones to convey different messages, but they rarely succeed because it is too tricky to remember what each tone represents. There are some ways to encode meaning into sounds, sometimes humorously called ‘earcons’ ! A rising tone suggests success or happiness, while a descending tone implies the opposite.
Beeps can get closer together to imply that some threshold is about to be met. Anti-bump sensors in cars can provide these beeps while reversing. Note that the driver can not usually map the spacing of the beeps to the distance from the object behind. However the driver can judge the spacing of the beeps relative to the spacing a second earlier, so he knows he is getting closer. This changing sound also has a natural limit as the reduction in the gap between beeps eventually leads to a constant tone implying that collision is imminent, or perhaps has already occurred.
A much less critical application is a kid’s music keyboard. We have one at home with five volume levels. When you turn the device on it always defaults to five – the loudest. It is always easier to convince a kid to turn up the music than to turn it down, so why did they not default to a quieter volume? An even better solution would be to remember the last used volume, but that might have a cost impact since some non-volatile storage would be required. Without that ideal option, try to pick the volume defaults to be the least disruptive.
These scattered examples of the use of sounds in the user interface might influence your thinking the next time you add a beep.