Lorelei Erisis taps the screen of a borrowed iPhone. The key of A, with kazoo-like resonance, fills her living room in Ayer, Mass.

Erisis taps another button labeled "start," takes a deep breath, and sings the word "he," trying to match the tone.

A number, 75 percent, pops onto the screen.

"My pitch was too low," Erisis says. "Oh well. Let me try again."

Erisis, a transgender woman, is trying out Eva, a mobile phone app that may be the first of its kind. Transgender men and women who want to raise or lower the pitch of their voice can go through a series of breathing and pitch exercises designed to help with what can be the most difficult characteristic to change — their voice.

"What I often hear is, 'I pass as a woman until I open my mouth,' " says Kathe Perez, a speech language pathologist who designed the Eva app.

Erisis plays the tone again. This time, before she speaks, Erisis places two fingers below her Adam's apple and pushes up, just a touch, to physically raise the pitch of her voice. Erisis, now 41, says she felt like a girl growing up, but did not begin the physical transition from male to female until she was 33. Just for fun, Erisis tries the pitch test with her preferred pronoun.

“She,” Erisis sings out. "Hey, 99 percent. It’s hilarious that 'she' brought me to 99 percent."

Erisis, who writes a column called “Ask a Transwoman," hears from many transgender women, and some men, who say, "Voice can be a real liability. There are definitely large parts of this country, even this state, where it’s dangerous to be trans. It can be a matter of life or death."

"Many of the people I work with will not go out in public because they have to talk," Perez adds. "Or they’ll go with people so that their wife or their friend will order for them at a restaurant. They’re afraid to open their mouths because the sound that comes out doesn’t match the person that’s sitting at that table."

There are lots of online programs. Some transgender men and women work one-on-one with a coach. Perez says it takes six months to a year of daily practice to permanently adjust one’s voice.

A screenshot of the Eva app

"It’s extremely difficult to override some of the early programming we have in our brains about how we express ourselves," she says. "So we retrain the voice by retraining the brain. They go together."

Transgender men — that is, women making the transition to men — can lengthen their vocal cords and develop deeper voices if they take testosterone. But for transgender women who begin the transition to female after puberty, hormone therapy does not make vocal chords shorter or thinner. Some transgender women have surgery to shorten their vocal cords, but the results are not predictable.

Learning to sound like a man or woman goes beyond pitch, says Adrienne Hancock, an assistant professor of speech at George Washington University who studies transgender voice and communication.

There's resonance. Hancock says imagine actor James Earl Jones humming an "M." As compared to, say, Marilyn Monroe.

And patterns of speech can be quite different for men and women, argues Celia Hooper, a dean at the University of North Carolina Greensboro who has taught speech and language classes for transgender men and women on and off since 1978.

"Let’s say I wanted to be a typical older male," Hooper says, offering an example. "I'd use short, clipped speech. 'Yep, nope, just like that.' "

Women are more likely to elaborate and use what Hooper calls flowery speech, "saying things like, 'Oh, it's just fabulous. That’s just marvelous.' " Or, laughs Hooper, "'Bless your heart.' "

Hooper has had clients watch soap operas, first with the sound up, then off.

"Not that you want to be like that, but soap operas are full of people who are either hyper-female or hyper-male, so you can get an idea of their behavior and then kind of reel it in because gender expression is on a continuum," Hooper says.

Erisis, the transgender woman, has discovered the implications of her position on that continuum.

"If I use a more submissive tone and a more questioning tone, people will be more likely to gender me as female," she says. "On the flip side, if I make statements, if I’m clear about what I’m saying, if I’m bold, people will very often be more likely to gender me as male."

So Erisis chooses, from one conversation to the next, whether she wants to be seen as female — and perhaps be taken less seriously — or seen as male.

"I have to make those little decisions every day, often several times a day," she says.

There is some debate about which physical characteristic most clearly signals our gender. Voice, says the speech language pathologist Perez, is a window into the emotional or spiritual self.

"[Voice] is indeed the organ of the soul," she says, quoting the poet Henry Wadsworth Longfellow.