Voice speed and pitch

Also called Speech rate, Speaking rate, Voice pitch, Prosody settings

The two settings that make a synthetic voice sound right, or wrong, for its owner, and why the app's default is almost never it.

What it is

Every text-to-speech voice has a speed (how many words a minute) and a pitch (how high or low), and both can be changed. An app ships with a default, usually a brisk adult rate at the voice's natural pitch. The person using it may want something quite different, and they are entitled to it.

These are small settings with a large effect on whether a voice feels like the person's own or like an announcement at a station.

Who it can help

Everyone whose aid speaks, and especially: children, who are given adult voices and need them lighter and higher; people who are hard to hear in noise, who need slower and lower; people with hearing loss in the family; people who listen to their own device for auditory scanning and want the private voice fast and the public voice clear.

Speed and pitch cannot fix a voice that is the wrong sex, accent or age; that is a choosing a voice problem. And the extremes sound synthetic: pushing pitch far from the voice's natural range makes it wobble, and very fast speech drops consonants.

How it works

Speed is usually a slider or a percentage. Normal conversational English runs at roughly 150 to 170 words a minute; many AAC users set their public voice slower, around 120 to 140, so that a listener in a noisy room catches it, and some experienced screen-reader users listen at three times that for their own use. Pitch is offset from the voice's base; a small shift, ten or twenty per cent, is usually enough to make a voice younger or older, and a large one breaks it.

Some systems allow different settings per situation (a slow, loud voice for the shop; a quicker one at home) and some allow emphasis marks or a rise at the end of a question. Volume is often a separate control from the device volume, so a person can have the device quiet and the voice loud.

Getting started

With the person choosing, set the speed so that you, standing two metres away with the radio on, can repeat every word first time. That is the public rate. Then let them try pitch a step at a time until it sounds like them, not like the default.

Write both numbers down in the communication passport and check them after any update or reset, because they are the first thing that comes back to default.

Where to get help

Any speech and language therapist working in AAC can advise on rate for intelligibility; the RCSLT is their professional body. AbilityNet documents where the speech-rate settings live on each platform, and Communication Matters is where AAC users compare notes on how they set theirs.