1.9 Ensure that all outputs under the control of the device can be perceived by users with restricted or no hearing

Rationale

Many telephone users, particularly those using assistive technologies, may use the telephone network despite hearing related disabilities.

If audio output in the form of spoken language is used to present information, users who cannot hear well enough to understand what is said will not be able to perceive the information being given. Not being able to hear audio outputs well enough to understand them is often due to a combination of poor hearing, inadequate sound quality and background noise. So by increasing the sound quality and taking steps to reduce background noise, even users with some hearing impairment will be able to understand the spoken information.

Often, telephones rely on intentional sounds such as beeps and chimes or incidental sounds such as motor noises and coins being dispensed to inform the user that something has happened. This is particularly the case for outputs from public payphones for example. If there is no corresponding visual indicator, users who cannot hear the sounds may be unaware that something is happening or that an output has occurred.

Directions and Techniques

Provide adequate quality sound

Speech output of telephone functions and information can be achieved using either pre-recorded audio or speech synthesis. If possible, use digitised pre-recorded speech which has been recorded in a professional studio and spoken by a trained announcer. Speech synthesis, whilst more flexible, is often of much poorer quality and may be difficult to understand for some users and in noisy environments.

Take steps to screen out background noise

Baffles or sound absorbing materials can be built into the handset casing. Audio output can be provided via a headset or earpiece. Ensure that all telephones are compatible with such devices. If audio output is provided via an audio transducer held to the ear, provide a means for effective wireless coupling to hearing aids. Mouthpiece microphones can include sidetone reduction to reduce the problem of ambient noise picked up by the microphone mixing with the incoming speech.

Allow the user to increase the sound level

Allow users to increase the sound level by up to 20dB. Ensure that all audible outputs are adjustable both in terms of volume and pitch and include both high and low frequencies in ring-tones etc.

For all audible cues, provide corresponding visual cues

Supplement audible cues, such as clicks, beeps and spoken alerts, with simultaneous corresponding visual cues, such as flashing indicator lights.

Provide visual and tactile indication of incoming calls

Users should be notified of incoming calls using visual and/or tactile signals. For fixed phones, a flashing light is the best methods. For mobile phones, which are often out of vision in a pocket or bag, vibration should also be used.

How you could check for this:

Self-test early prototypes

Designers can run simple hearing tests themselves on an early prototype, by simulating various degrees of hearing loss or environmental conditions. Wearing earplugs, industrial ear protectors or noise-cancelling headphones can considerably reduce all sound, although it is difficult to reach complete loss of hearing.Partial hearing loss may be even more difficult to simulate accurately, since the degradation is often not uniform across the frequency range. It may be greater at some frequencies, particularly the high or low ends of the hearing spectrum.To simulate noisy environments, it is best to test the prototype in situ if this is practical. Otherwise, recordings of background noise from typical environments can be used. In all cases, care should be taken when running these tests since the user whose hearing is reduced may not be able to hear other important sounds, such as verbal warnings from experimenters, alerts, or fire alarms.

Test with real users

During development, you should test the prototype in a realistic situation with real people who have various forms of hearing impairment and use a variety of assistive technologies. In particular, you should include people who are recently impaired and have not yet developed enhanced perception or coping methods.
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