When a device uses audio output to provide important information, users can have difficulty hearing the information if they are in a public area. Users need to be able to adjust the volume so they can hear the information.
If the product is in an environment with a high noise level, users may need to adjust the volume so the voice output can be heard.
When a product uses audio to communicate important information, individuals using personal headphones, amplifiers, audio couplers and other audio processing devices need a place to plug the device into the product in a standard way. This gives the user the ability to listen privately to the information.
Synthetic or digitally stored speech can be used for:
- Prompts or fixed messages
- Error or help messages
- Output of contents of screen
For non-speech output, such as acoustic signals to attract attention, use a frequency between 300Hz and 3000Hz. Acoustic signals include: ringing signals and equipment warning signals e.g. error "bleep".
Problems encountered by disabled people and the ageing population using audio output technology
Some users with visual impairments may find it difficult to use ICT systems without auditory displays (e.g. acoustic signals and speech output), to complement visual information.
People with a hearing impairment often have difficulty in understanding synthetic speech output since it tends to have less redundancy than natural speech. The facility to repeat a message is frequently essential rather than just desirable.
Poor quality speech output may prove difficult to understand.
Background noise may prevent users from hearing information or feedback.
A phsyically impaired user may find it difficult to easily reach the volume control.
Long and complicated instructions may cause confusion to some cognitively impaired users.
Background noise may prevent cognitively impaired users from understanding instructions or feedback.
Some members of the ageing population may have difficulty understanding poor quality speech output.
Background noise may prevent some users from hearing and/or understanding instructions or feedback.
IBM (2008) recommend:
- Provide a physical volume control on the system which can be easily reached or a software interface for adjusting the volume
- The volume control should provide amplification up to a level of at least 65 dB. Where the ambient noise level of the environment is above 45 dB, a volume gain of at least 20 dB above the ambient level should be available
- Provide a method to automatically reset the volume to the default level after use
IBM (2008) recommends:
- Provide a standard audio connector so individuals using personal headphones, amplifiers, audio couplers and other audio processing devices can plug these devices into the product in a standard way
- Voice warnings should be presented in a voice that is different from other voices that will be heard in the task situation
- If synthesized speech is used for other types of information in addition to warnings, the user needs to be able to distinguish between these messages
- Maximise the intelligibility of the messages
- Make the voice as natural as possible so people are more likely to accept it
- If the message is missed, it is beneficial for people to be able to replay it
- If the message is familiar, the ability to interrupt the message would be beneficial for experienced users
- Where the choice of messages is relatively limited, human voices are preferred because synthetic speech is less intelligible and less preferred
- Use non-speech audio messages only for the purposes of alerting
- ETSI EG 202 116 (2002) Human Factors (HF); Guidelines for ICT products and services: Design for all
- ETSI ES 202 076 (2002) - Human Factors (HF); User Interfaces; Generic spoken command vocabulary for ICT devices and services
- ISO/CD 24500 Guidelines for all people, including elderly persons and persons with disabilities - Auditory signals on consumer products
- ISO/CD 24501 Guidelines for all people including elderly persons and persons with disabilities - Auditory signals on consumer products - Sound pressure levels of signals for the elderly and in noisy conditions
- ISO/TR 22411 (2008) Ergonomics data and guidelines for the application of ISO/IEC Guide 71 to products and services to address the needs of older persons and persons with disabilities
- ITU-T P.85 (1994) A method for subjective performance assessment of the quality of speech voice output devices
- JIS S 0013 (2002) Guidelines for the elderly and people with disabilities - Auditory signals on consumer products
- JIS S 0014 (2003) Guidelines for the elderly and people with disabilities - Auditory signals on consumer products - Sound pressure levels of signals for the elderly and in noisy conditions
- Audio Input
- Computer Hardware
- Gill, J. (ed) (2005) Making Life Easier: How New Telecommunication Services Could Benefit People With Disabilities. [accessed 27/01/09]
- Thompson, T. (2005) Speech Technology for Persons With Disabilities: Are We Breaking Down Barriers or Creating New Ones? Speech Technology [online]. [accessed 28/01/09]
- Mobile Phones
- User Interfaces and Interface Transmission Technologies to Assistive Devices
- Waterworth, J A and Thomas, C T (1985). Why is Synthetic Speech Harder to Remember than Natural Speech?. In Proceedings of ACM CHI'85 Conference on Human Factors in Computer Systems (San Francisco, USA, 1985). New York: ACM.
- Wayfinding Technologies
- Wolters, M. K., Campbell, P., DePlacido, C., Liddell, A. & Owens, D. (2008) What Makes Synthetic Speech Difficult for Older People to Understand? PDF. [accessed 28/01/09]