Pitch
No lower than 125-150Hz and no higher than 5kHz
Caution: Some instruments do not render very low
or very high pitches well
Register
Ideally, a 2 to 3 octave difference should be
used to distinguish earcons
Avoid if user has to make absolute judgment of earcons
that vary in relative pitch as well
Timbre
Effective method of distinguishing earcons
Use similar timbres with semantically similar
objects, actions or events
Instruments can either have a indefinite or discrete
lifetime, use appropriately