The word ‘egophony’ is what the doctor calls it when you’re having a stethoscope put to your chest, to check your breathing. So it’s being used as a metaphor for diagnosing who you are, where you’re from.” Chris Chapman’s work is one of a number of remarkable explorations in the Wellcome Collection’s This Is a Voice exhibition. The notion of voice and identity is one we will have all considered in terms of what it says about us socially – class and geography. And, of course, the way in which class can demand you erase your geographical self, depending on which class you’re in.

The works in this show push those questions further into the self, into gender, identity; “the noises that we make to communicate with each other that aren’t linguistic,” as Chapman puts it. He has made two films, one about a therapy programme run by the London Institute of Psychiatry, in which patients with psychosis create avatars, in order to talk back to their interior voices, and one about people who are transitioning from one gender to the other, and the work they do to retrain their voices.

“With gender transition,” he explains, “80% is from male to female, where in order to change the voice, it’s all about voice therapy. Whereas with female-to-male transition, you just take testosterone, and within three to four weeks, your voice drops. I spoke to a man who transitioned from female to male and he found validation through a phone call, when they called him ‘Sir’, as opposed to ‘Miss’. That was the tipping point for him.” Another of his subjects is Adèle Anderson, the cabaret singer from Fascinating Aïda, who transitioned in the 1970s; she gives me a wonderfully long and profound view on the voice and the self, and how much has changed for people who are trans.

“There used to be this thing called ‘stealth’, and the marker of a really successful trans woman was that nobody would ever guess in a million years that she was ever anything other than she is now. That would put a great deal of strain on you, to deny everything that you were before, you’d be terrified of meeting anybody who knew you before. And when you transitioned, the voice was the thing that everybody feared: that they might look fantastic, but as soon as they opened their mouths … particularly in the supermarket, when people aren’t really looking at you, they’ve just clocked that you’re female. But then you start talking to them, and you see the look in their eyes.”

Although you can have surgery to shave your trachea and shorten your vocal cords, you can also retrain your voice. Anderson has been to a specialist who said that her cords were clearly male, but that she used them in a female way. She then sings to me the difference between a soprano and a countertenor, and it is immediately plain that pitch isn’t the determining feature of gender, vocally; there are women with very deep voices and men with light, high ones, and yet we understand instinctively who we’re talking to.

“There are three parts,” Chapman says, “pitch, intonation and resonance. Then there are non-vocal characteristics; the use of language, the way that you speak. Men are more likely to interrupt women than they are when they’re having a conversation with another man. Women are much more likely to use hedging words, ‘perhaps’, ‘maybe’, whereas men will use ‘must’, ‘will’, ‘absolutely’.” The idea of being able to train your voice, when it’s so integral to your identity, is what makes this exhibition so interesting. It’s like being able to train your fingerprint.

This comes across forcefully in a beautiful, haunting film by the artist Katarina Zdjelar, The Perfect Sound. Made in 2009, the work observes an accent removal class in Birmingham, as a speech therapist teaches a recent immigrant how to sound more English, or at least, less un-English. With bare, quasi-medical lighting and a sparse, intense atmosphere, we watch the face of the therapist as he chants meaningless sounds. It is unaccountably moving, inexplicably frightening: a kind of animal intimacy develops between the two men as they echo one another. Zdjelar describes the process of neutralising the voice so that it becomes not a siren of one’s difference, but a cloak of invisibility, allowing the man into his environment, allowing him to become unnoticeable. I don’t think I’ve seen anything that describes so closely and with such emotional immediacy the state of being foreign, of having to remould yourself to suit to your new home.

This theme is extended by the artist Lawrence Abu Hamdan, who made a film about a Palestinian refugee, Mohamad, in 2012. It moves us into the territory of the voice as evidence, the test that you are who you say you are. Mohamad is an undocumented asylum seeker who mispronounced three words in an “accent test” – the UK Border Agency’s language analysis is highly contested, and as a legal tool for removal, incredibly shonky. When you describe Mohamad’s case to any academic in the field of migration, they always ask who his lawyer is. But the fact remains that Mohamad is now being deported, and the portraits capture his state of purgatory – undone by his voice, he now belongs nowhere, and all the apparatus of life has been dismantled from under him.

Yet just as your voice can betray you, or can work or fail to work as a mask, it is also, obviously, a powerful source of self-expression. “I love my voice,” says Anderson, “and it’s given me a very good living. It was interesting, Chris told me while we were making the film that some trans women said they found it quite difficult to come to terms with their new voice, because they’d had to learn it later in life. For somebody who has to learn a completely new voice that they’re going to stick on to themselves, it can be difficult. I took out all the bass from mine, and I lightened it, but I never wanted to have a little girlie voice. I thought that wouldn’t suit me. It’s always been a part of me and I’ve always used it.”