Designing Effective Speech Interfaces

Non-Speech Audio/Auditory Icons

An auditory icon is a non-speech audio signal based on a real-world sound. For example, the sound of a police siren signaling an emergency is an auditory icon. You can alter the character of the sound to imply a change in the characteristic of the object. For example, a cash register sound can get louder the more money is deposited.

Use Standard Sounds with Their Usual Meanings

Many auditory icons are already used in other applications. If you are going to use these, be sure to use them in an expected context. Table 10.3 lists some common auditory icons and their uses.

Auditory Icon	Usual Meaning
Busy signal	Action is not available because it's already being used by another
Beep	Error or attention
Siren	Emergency
Dial tone	Open line, ready

Table 10.3 Auditory Icons and Their Meanings

Stay within an Octave for a Sequence

If you are using a sequence of tones that must be distinguished from another sequence, keep each sequence within an octave so that you can use the octave change as a signal of a different sequence.

Use appropriate scale movements. For example, rising tones imply “up” and falling tones imply “down.”

Rising tones imply “up.”

Use Volume to Signify Meaning

A tone that grows quieter indicates that something is going down. A tone that grows louder signifies that something is going up. Avoid very loud noises unless you purposely need to startle users.