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If you are on a first date, listen very closely to the sound of your partner's voice because it might reveal if they fancy you, according to researchers.

It's not about what your date is saying, but the pitch of their voice.

If they lower their pitch, it could be a subtle, subconscious sign they find you attractive, the study, in The Royal Society Proceedings B journal, suggests.

Experts say it is probably an evolutionary tool to attract a mate.

The study

The researchers listened in on 30 speed-daters meeting at a cafe.

Each date lasted six minutes, with the men rotating around the tables until they had dated all of the women in the room.

Between each interaction, the men and women indicated their preference for the person the had just met - whether they liked them and would want to meet again - marking a "Yes" or "No" next to the date's name.

When the researchers listened back to the conversations, they found that men and women tended to adopt a slightly lower voice during the dates with a partner they fancied.

Men also spoke at a lower pitch with women who had received lots of "Yes" responses from the other men in the dating room, even if they rated her with a "No" themselves.

Women, by contrast, lowered their voices only for men they both found attractive themselves and who had been rated highly by the other women in the room too.

What's going on?

It's not the only study to find this phenomenon but it is the first in a real-life setting, says lead researcher Katarzyna Pisanski from the University of Sussex School of Psychology.

And although it didn't include a large number of people, the hundreds of dates observed between the participants provided enough data to give a significant result.

"I was a little bit surprised that women also lowered their pitch if they liked a man," she said.

"Quite a few studies have shown men tend to favour a higher pitch in women because it is feminine and youthful, while women tend to like men to have deeper voices that are seen as more masculine and linked to testosterone."

Research suggests women today speak at a deeper pitch than their mothers or grandmothers.

For that work, Cecilia Pemberton, at the University of South Australia, compared archival recordings of women talking in 1945 with recordings taken in the early 1990s.

Dr Pisanski said: "Perhaps things are changing and women are trying to portray other values when they use a lower pitch.

"It might communicate competence, maturity or even dominance."

Lower, quieter speech might also be more intimate.

Dr George Fieldman, an evolutionary psychologist and member of the British Psychological Society, said it was possible the competitive situation of speed-dating might have made the women adopt a more dominant pitch of voice to attract a mate.

"If they were on their own with a man, then perhaps they would use a higher pitch," he said.

"But when they are in a group situation competing against other women, they might want to keep their pitch lower. It is more discreet. That's my hunch."