I recommend looking at this smashing magazine article Designing With Audio: What Is Sound Good For? for additional inputs on how sound is used to communicate feedback and bring about interaction with the users. To quote the article :
MOBILE
Much of the Web is moving to mobile, which of course entails
smaller screens and people on the go. But besides creating
mobile-specific websites, there are ways to augment the mobile
experience with audio when people aren’t looking at or can’t interact
with the screen. A great example is GPS and turn-by-turn navigation
systems that speak directions (either as part of a dedicated device or
from a smartphone app). While audio isn’t yet native to mobile
websites and apps, it is native to smartphones to indicate new email,
incoming text messages and calendar events.
GAMING
For those who play video games, audio is integral to setting
the mood, environment and situation, and it engages the user
tremendously. First-person shooter games such as Halo and Call of Duty
rely on audio feedback to show cause and effect — for example, the
sound of a gun shooting and the moment of impact on the enemy. Or
consider Wii Sports: the smash of the ball in tennis, the crack of the
bat in baseball, and the cheer of fans all help to blur the line
between the very physical game and the digital world.
CONSUMER DEVICES
More and more of our everyday devices use audio feedback: a Bluetooth
headset tells you who is calling, Nike+ tells you your current
distance travelled and pace, and cars beep to help you park.
Other examples given by the article are :
Audio can be used to offer information, either when no screen is
available or when certain details would be better captured as audio.
The Jambox by Jawbone tells the user when they need to recharge
the battery. The Leapfrog LeapPad takes this one step further by
specifying the type of batteries it needs!
Similarly Audi also uses a parking sensor to tell drivers that they are getting too close to a parked car as shown in this video
I also recommend looking at this research article Using Sound to Enhance Users’ Experiences of Mobile
Applications which talks about how the use of sound can enhance the user experience of users while interacting with mobile devices. To quote the research paper
Tests show that users appreciated the applications for their ease
of use, for being fun and effective to use and for allowing users to
interact directly with the environment rather than with abstractions
of the same. The multimodal user interfaces contributed significantly
to the overall user experience.
With regards to best practices to using Audio with regards to interactions,I recommend looking at this smashing magazine article Guidelines For Designing With Audio
To briefly summarize the article :
CHOOSE THE RIGHT TYPE OF AUDIO
Audio can be non-verbal sounds, sometimes called “earcons,” or can be words,
sometimes called prompts,
and choosing the right type is important. Meaning can be embedded in
an earcon in such a way that a short non-intrusive sound can represent
something much larger. Think of the sound that confirms that a text
message has been sent on an iPhone: the sound effectively represents
the action by suggesting motion and movement away from the user.
Another example is the parking-assist system in a car; the intensity
and pitch of sounds create a sense of urgency to let the driver know
their distance from the nearest car.
EMBED MEANING IN AUDIO EARCONS
Designing sound is complex, and audio designers will want to consider
pitch, timbre, loudness, duration and direction to create the right
sound. For details on how these should be considered in earcon design,
consult “Auditory Interfaces: A Design Platform”
DESIGN IN CONTEXT
Whether you are designing earcons or prompts, consider the particular context of the user, both physically and
emotionally. If you are designing audio instructions or information,
consider these factors:
- Is there a way to differentiate between a novice user (i.e. someone who needs more hand-holding) and an expert user? This could be done by
keeping track of the number of interactions that the user has with the
device, and tailoring an audio experience for first-time users, while
playing shortened prompts to expert users.
- If the device has a screen, do you know whether the user will rely on visual feedback to complete their task? If so, audio might be a
secondary feedback mechanism or might not be needed at all. Audio
could be tailored specifically for these situations by playing less or
different audio. Knowing where the device is in relation to the user
could be done with certain sensors or accelerometers or derived from
how the interaction was initiated.
- Many other contexts warrant tailoring the audio experience. With GPS, for example, you can determine whether the user is driving (using
their speed). Sometimes the current state of the device is relevant
and can indicate the proximity of the user or their level of
engagement.
The article also provides some design guidelines about how to use audio :
- Use language that users understand. Stay away from lingo, jargon and technical terms that would make sense to the company but not to the
end user.
- Do not overload the user with too much information at once. Limit the number of audio menu options. Audio is linear, time-sensitive and
transient, unlike the Web and other visual feedback media in which
users can take time to read, process and select. Research has shown
that remembering more than five options from an audio menu is hard.
Users will often listen to all choices before picking one, so a long
list will limit their ability to remember them all.
- When writing prompts that require users to make a choice, structure them so that the menu option comes before the action; for example “For
y, press x,” instead of “Press x for y.” The user will more easily be
able to identify the option they want and listen more attentively for
the action.
However with all of this said, Don’t forget where ever possible audio should not be used as a sole identifier of instruction or action. As per the W3 guidelines on accessiblity
1.3.3 Sensory Characteristics: Instructions provided for understanding and operating content do not rely solely on sensory characteristics of
components such as shape, size, visual location, orientation, or
sound.
Remember to consider assistive technology when designing systems with sound, you want to ensure you dont override assistive technologies like screen readers by having additional distracting sounds which could cause confusion
