STICK your tongue out at Susan Date? How dare you. How could you do that to someone so non-threatening. Date looks like everyone's aunt in her sensible shoes and the kind of clothes that forgive a second helping. She's the type you'd invite for a sherry. But her voice changes the impression. She controls an audience with it. When she lowers the pitch, she's the dusky-voiced Lauren Bacall. When she raises it, she becomes a little old lady, rummaging the stalls of Portobello Road. ''Here's one to use when you call in sick at the office,'' then she switched into a flu-stricken, sympathy-inducing nasal number. She contorts her facial features like a mime artist and just one of her screeches could shatter crystal. Strangers, at first, hesitate when she invites them to feel her rib cage. But people respond to her challenges by getting down in front of her on all fours. And several dozen did recently when the British speech specialist held a workshop in the Fringe Theatre. ''Your Voice is You'' was a combination of lecture and exercises designed to show everyday folks, as well as thespians, the voice's potential for change and improvement. Use the voice as a tool to bolster confidence, improve self-images and achieve success in your own field, says Date. But it takes work and the will to change. Workshop students mimicked everything Date did - snapping a finger against the cheek, pinching the nose, dropping the head towards the knees and convulsing in soundless laughter. The accomplished actress/director and producer was in Hongkong, accompanying a group of actors from the Guildford School of Acting in Surrey for their performance in Hard Times. She is also the assistant principal at Guildford. Vocal chords need proper care and gentle exercise, including proper alignment of the head and spine, she said, then demonstrated differences between pitch and resonance, lectured about soft palate and larynx and made many adults, weary from a day's work,sit up straight. The students at Guildford put their voices on tape then measure their progress months later, by playing it back. Any student who needs a brush-up on a specific accent goes to the school's ''accent'' library where thousands of examples are on tape. ''We've got everything. If you want to sound like an Irishman who has lived in Wales for five years, no problem.'' Date studied with opera singer-turned voice pedagogue Jo Estell and graduated from Webber-Douglas and The Central School of Speech and Drama in London. ''I like my voice most of the time,'' she continued. ''But I am lazy. So it's better to say I like it or do something to change it.'' Date's work isn't limited to actors. A group of ''ancient'' women who were worried about ageing voices enlisted her help. She advised them on gentle voice exercises. They can minimise or postpone the ageing process. One school invited her to observe the teachers to find out why they finished the day with tired voices. ''They tried to top the noise of the kids by using a higher pitch. I advised them to lower their pitch. It is less stressful and taxing. A lower voice, not a louder voice, is commanding. you want to listen to it. It also emanates power and maintains a status.'' Businessmen, especially salesmen, come to change their accent. ''If they're up for a promotion or there's an important sales presentation coming up. They tell me they want to speak more posh. What they're really talking about is the quality of the tone. It's a matter of resonance.'' Changing an accent isn't difficult. But it requires doing drills with tapes. Improving the quality of the voice is more complex. It involves checking the intonation pattern, among other things. Date pointed out that everyone - regardless of mother tongue - has an equal opportunity to change and improve their voice. ''It's basically habit. You can meet a Hongkong-born Chinese living in the UK and he will have no trouble with the local accent. Environment is a big part of it.'' We use our best voice in the bathroom, not at a party, she minds. ''You can hurt your voice at a party with all the smoke and trying to talk over the noise. ''But bathrooms are acoustically appealing. They're warm and cool and people who sing in the tub or shower, are usually happy or content. ''Often that voice is our best one.''